掲載種別：研究論文（学術雑誌）   出版者・発行元：Springer Science and Business Media LLC  

We show a new mechanism for baryogenesis where the reheating temperature can
be smaller than the electroweak scale. The baryon number symmetry is violated
by a dimension nine operator which conserves a baryon parity. A high energy
quark from the decay of a heavy particle, e.g. inflaton, modulus or gravitino,
undergoes flavor oscillation, and is thermalized due to the scatterings with
the ambient thermal plasma. We point out that the baryon asymmetry of our
universe can be generated due to the scatterings via the baryon number
violating operator. Our scenario can be tested in neutron-antineutron
oscillation experiments as well as other terrestrial experiments.

DOI： 10.1007/JHEP07(2020)174

arXiv

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その他リンク： http://arxiv.org/pdf/1912.08797v1

掲載種別：研究論文（学術雑誌）   出版者・発行元：Springer Science and Business Media LLC  

We consider a model with three right-handed neutrinos in which Yukawa
coupling constants and Majorana masses are obtained by requiring the modular
$A_4$ symmetry. It has been shown that the model can explain mass hierarchies
and mixing patterns of charged leptons and neutrinos with the seesaw mechanism.
In this article we investigate the leptogenesis by decays of right-handed
neutrinos in this model. It is shown that masses of right-handed neutrinos are
about $10^{13}$ GeV in order to account for the observed baryon asymmetry of
the universe. Furthermore, the positive sign of the baryon asymmetry is
obtained only for the limited ranges of mixing angles and CP violation phases
of active neutrinos, which can be tested by future neutrino experiments.

DOI： 10.1007/JHEP01(2020)144

arXiv

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その他リンク： http://arxiv.org/pdf/1909.06520v1

掲載種別：研究論文（学術雑誌）   出版者・発行元：Springer Science and Business Media LLC  

We investigate a resonant leptogenesis scenario by quasi-degenerate
right-handed neutrinos which have TeV-scale masses. Especially, we consider the
case when two right-handed neutrinos are responsible to leptogenesis and the
seesaw mechanism for active neutrino masses, and assume that the CP violation
occurs only in the mixing matrix of active neutrinos. In this case the sign of
the baryon asymmetry depends on the Dirac and Majorana CP phases as well as the
mixing angle of the right-handed neutrinos. It is shown how the yield of the
baryon asymmetry correlates with these parameters. In addition, we find that
the effective neutrino mass in the neutrinoless double beta decay receives an
additional constraint in order to account for the observed baryon asymmetry
depending on the masses and mixing angle of right-handed neutrinos.

DOI： 10.1007/JHEP09(2019)089

arXiv

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その他リンク： http://arxiv.org/pdf/1812.11323v3

掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.physletb.2018.09.004

Web of Science

arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER PHYSICAL SOC  

We consider a baryogenesis scenario via the oscillation of right-handed neutrinos with Majorana masses of the order of GeV, which are also responsible for neutrino masses by the seesaw mechanism. We study how the initial condition alters the prediction of the present baryon asymmetry by this mechanism. It is usually assumed that the abundance of right-handed neutrinos is zero after the reheating of the inflationary universe and they are produced in scattering processes by the renomalizable Yukawa interaction. However, the higher-dimensional operator with right-handed neutrinos may provide an additional production which is most effective at the reheating epoch. It is shown that such an initial abundance of right-handed neutrinos can significantly modify the prediction when the strong washout of the asymmetry is absent. This leads to the parameter space of the model for the successful baryogenesis being enlarged.

DOI： 10.1103/PhysRevD.96.083010

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

Heavy Majorana neutrinos are predicted in addition to ordinary active neutrinos in the models with the seesaw mechanism. We investigate the lepton number violation (LNV) in B decays induced by such a heavy neutrino Nwith GeV- scale mass. Especially, we consider the decay channel B+ -> mu(+) N -> mu(+) mu(+) pi(-) and derive the sensitivity limits on the mixing angle Theta(mu) by the future search experiments at Belle II and in e(+) e(-) collisions at the Future Circular Collider (FCC-ee). (C) 2016 The Author(s). Published by Elsevier B.V.

DOI： 10.1016/j.physletb.2016.10.070

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arXiv

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記述言語：英語   出版者・発行元：IOP PUBLISHING LTD  

This paper describes the physics case for a new fixed target facility at CERN SPS. The SHiP (search for hidden particles) experiment is intended to hunt for new physics in the largely unexplored domain of very weakly interacting particles with masses below the Fermi scale, inaccessible to the LHC experiments, and to study tau neutrino physics. The same proton beam setup can be used later to look for decays of tau-leptons with lepton flavour number non-conservation, tau -> 3 mu and to search for weakly-interacting sub-GeV dark matter candidates. We discuss the evidence for physics beyond the standard model and describe interactions between new particles and four different portals-scalars, vectors, fermions or axion-like particles. We discuss motivations for different models, manifesting themselves via these interactions, and how they can be probed with the SHiP experiment and present several case studies. The prospects to search for relatively light SUSY and composite particles at SHiP are also discussed. We demonstrate that the SHiP experiment has a unique potential to discover new physics and can directly probe a number of solutions of beyond the standard model puzzles, such as neutrino masses, baryon asymmetry of the Universe, dark matter, and inflation.

DOI： 10.1088/0034-4885/79/12/124201

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS INC  

The Starobinsky model of inflation, consistent with Planck 2015, has a peculiar form of the action, which contains the leading Einstein term R, the R-2 term with a huge coefficient, and negligible higher-order terms. We propose an explanation of this form based on compactification of extra dimensions. Once tuning of order 10(-4) is accepted to suppress the linear term R, we no longer have to suppress higher-order terms, which give nontrivial corrections to the Starobinsky model. We show our predictions of the spectral index, its runnings, and the tensor-to-scalar ratio. Finally, we discuss a possibility that quantum gravity may appear at the scale Lambda greater than or similar to 5 x 10(15) GeV.

DOI： 10.1093/ptep/ptw161

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

We consider the neutrinoless double beta (0 nu beta beta) decay in the nu MSM, in which three right-handed neutrinos with masses below the electroweak scale are additionally introduced to the Standard Model. In this model there appear three heavy neutral leptons N-1, N-2, and N-3 corresponding to right-handed neutrinos. It has been known that the lightest one N-1 with keV mass, which is a candidate for dark matter, gives a negligible contribution to the 0 nu beta beta decay. By contrast, the heavier ones N-2 and N-3, which are responsible to the seesaw mechanism of neutrino masses and baryogenesis, give the destructive contribution (compared with one from active neutrinos). This is because their mass degeneracy at high precision has been assumed, which is expected by analytical studies of baryogenesis. In this analysis, we find that the effective mass of the 0 nu beta beta decay becomes larger than one from active neutrinos due to the N-2 and N-3 constructive contribution when the mass difference becomes larger and the mass ordering of active neutrinos is inverted. Such a possibility will be explored by the current and near future experiments of the 0 nu beta beta decay. (C) 2016 The Author(s). Published by Elsevier B.V.

DOI： 10.1016/j.physletb.2016.09.044

Web of Science

arXiv

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier BV  

DOI： 10.1016/j.physletb.2016.07.001

arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS INC  

We argue that the COMET experiment-a dedicated experiment for the mu-e conversion search-has a good potential to search for heavy neutrinos in the mass range 1 MeV less than or similar to M less than or similar to 100 MeV. The stopped muons captured by the target nuclei or decaying in orbit efficiently produce heavy neutrinos via the active-sterile mixing. The produced heavy neutrinos then decay to electronpositron pairs (plus an active neutrino), which charged particles hit the cylindrical drift chamber surrounding the target. If the backgrounds from gamma rays are sufficiently rejected by some method, the expected sensitivity becomes comparable to the PS191 bound when the COMET experiment achieves similar to 10(17) stopping muons in the target.

DOI： 10.1093/ptep/ptw011

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arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

We consider the Standard Model extended by right-handed neutrinos to explain massive neutrinos through the seesaw mechanism. The new fermion can be observed when it has a sufficiently small mass and large mixings to left-handed neutrinos. If such a particle is the lightest right-handed neutrino, its contribution to the mass matrix of active neutrinos needs to be canceled by that of a heavier one. Yukawa couplings of the heavier one are then larger than those of the lightest one. We show that the perturbativity condition gives a severe upper bound on the mixing of the lightest right-handed neutrino, depending on the masses of heavier ones. Models of high energy phenomena, such as leptogenesis, can be constrained by low energy experiments. (C) 2015 The Authors. Published by Elsevier B.V.

DOI： 10.1016/j.physletb.2015.12.013

Web of Science

arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Physical Society  

We consider the Standard Model with right-handed neutrinos to explain the masses of active neutrinos by the seesaw mechanism. Since active neutrinos as well as heavy neutral leptons are Majorana fermions in this case, the lepton number violating process can be induced. We discuss the inverse neutrinoless double beta decay e-e-→W-W- in the framework of the seesaw mechanism and its detectability at future colliders. It is shown that the cross section can be 17 fb for s=3 TeV even with the stringent constraint from the neutrinoless double beta decays if three (or more) right-handed neutrinos exist. In such a case, the future e-e- colliders can test lepton number violation mediated by a right-handed neutrino lighter than about 10 TeV.

DOI： 10.1103/PhysRevD.92.094012

Scopus

arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.physletb.2015.01.049

Web of Science

arXiv

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記述言語：英語   出版者・発行元：SPRINGER  

DOI： 10.1007/JHEP02(2015)028

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physical Society of Japan  

We consider an extension of the Standard Model by two right-handed neutrinos, especially with masses lighter than the charged K meson. This simple model can realize the seesaw mechanism for neutrino masses and also baryogenesis by flavor oscillations of right-handed neutrinos. We summarize the constraints on right-handed neutrinos from direct searches as well as big bang nucleosynthesis. It is then found that the possible range for the quasi-degenerate mass of righthanded neutrinos is M&lt
inf&gt
N&lt
/inf&gt
≥ 163MeV for the normal hierarchy of neutrino masses, while M&lt
inf&gt
N&lt
/inf&gt
= 188-269MeV and M&lt
inf&gt
N&lt
/inf&gt
≥ 285MeV for the inverted hierarchy case. Furthermore, we find in the latter case that the possible value of the Majorana phase is restricted for M&lt
inf&gt
N&lt
/inf&gt
= 188-350 MeV, which leads to the fact that the rate of neutrinoless double beta decay is also limited.

DOI： 10.1093/ptep/ptt094

Scopus

arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/ptep/ptt094

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We investigate baryogenesis in the nu MSM (neutrino Minimal Standard Model), which is the SM extended by three right-handed neutrinos with masses below the electroweak scale. The baryon asymmetry of the universe can be generated by the mechanism via flavor oscillation of right-handed (sterile) neutrinos which are responsible to masses of active neutrinos confirmed by various experiments. We present the kinetic equations for the matrix of densities of leptons which describe the generation of asymmetries. Especially, the momentum dependence of the matrix of densities is taken into account. By solving these equations numerically, it is found that the momentum distribution is significantly distorted from the equilibrium one, since the production for the modes with lower momenta k << T (T is the temperature of the universe) is enhanced, while suppressed for higher modes. As a result, the most important mode for the yields of sterile neutrinos as well as the baryon asymmetry is k similar or equal to 2 T, which is smaller than < k > inferred from the thermal average. The comparison with the previous works is also discussed.

DOI： 10.1088/1475-7516/2012/02/021

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arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：SPRINGER  

We study production of sterile neutrinos in the atmosphere and their detection at Super-Kamiokande. A sterile neutrino in the mass range 1 MeV less than or similar to M<INF>N</INF> less than or similar to 105 MeV is produced by muon or pion decay, and decays to an electron-positron pair and an active neutrino. Such a decay of the sterile neutrino leaves two electron-like Cherenkov rings in the detector. We estimate the sterile neutrino flux from the well-established active neutrino fluxes and study the number of the decay events in the detector. The upper bounds for the active-sterile mixings are obtained by comparing the 2e-like events from the sterile neutrino decays and the observed data by Super-Kamiokande. The upper bound for the muon type mixing Theta<INF>& is found to be vertical bar Theta<INF>&<SUP>2</SUP> less than or similar to 5 x 10<SUP>-5</SUP> for 20MeV less than or similar to M<INF>N</INF> less than or similar to 80MeV, which is significantly loosened compared to the previous estimation. We demonstrate that the opening angle and the total energy of the rings may serve as diagnostic tools to discover the sterile neutrinos in further data accumulation and future upgraded facilities. The directional asymmetry of the events is a sensitive measure of the diminishment of the sterile neutrino flux due to the decays on the way to the detector.

DOI： 10.1007/JHEP07(2012)112

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arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：SPRINGER  

We investigate mixing of neutrinos in the vMSM (neutrino Minimal Standard Model), which is the MSM extended by three right-handed neutrinos. Especially, we study elements of the mixing matrix Theta(alpha I) between three left-handed neutrinos v(L alpha) (alpha = e, mu, tau) and two sterile neutrinos N-I (I = 2, 3) which are responsible to the seesaw mechanism generating the suppressed masses of active neutrinos as well as the generation of the baryon asymmetry of the universe. It is shown that Theta(eI) can be suppressed by many orders of magnitude compared with Theta(mu I) and Theta(tau I), when the Chooz angle theta(13) is large in the normal hierarchy of active neutrino masses. We then discuss the neutrinoless double beta decay in this framework by taking into account the contributions not only from active neutrinos but also from all the three sterile neutrinos. It is shown that N-2 and N-3 give substantial, destructive contributions when their masses are smaller than a few 100 MeV, and as a results Theta(eI) receive no stringent constraint from the bounds on such decays. Finally, we discuss the impacts of the obtained results on the direct searches of N-2,N-3 in meson decays for the case when N-2,N-3 are lighter than pion mass. We show that there exists the allowed region for N-2,N-3 with such small masses in the normal hierarchy case even if the current bound on the lifetimes of N-2,N-3 from the big bang nucleosynthesis is imposed. It is also pointed out that the direct search by using pi(+) -> e(+) + N-2,N-3 and K+ -> e(+) + N-2,N-3 might miss such N-2,N-3 since the branching ratios can be extremely small due to the cancellation in Theta(eI), but the search by K+ -> mu(+) + N-2,N-3 can cover the whole allowed region by improving the measurement of the branching ratio by a factor of 5.

DOI： 10.1007/JHEP04(2011)011

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arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

We investigate baryogenesis in the nu MSM, which is the Minimal Standard Model (MSM) extended by three right-handed neutrinos with Majorana masses smaller than the weak scale. In this model the baryon asymmetry of the universe (BAU) is generated via flavour oscillation between right-handed neutrinos. We consider the case when BAU is solely originated from the CP violation in the mixing matrix of active neutrinos. We perform analytical and numerical estimations of the yield of BAU, and show how BAU depends on mixing angles and CP violating phases. It is found that the asymmetry in the inverted hierarchy for neutrino masses receives a suppression factor of about 4% comparing with the normal hierarchy case. It is, however, pointed out that, when theta(13) = 0 and theta(23) = pi/4, baryogenesis in the normal hierarchy becomes ineffective, and hence the inverted hierarchy case becomes significant to account for the present BAU. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physletb.2010.07.016

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：PROGRESS THEORETICAL PHYSICS PUBLICATION OFFICE  

We investigate particle production from coherent oscillation using the method based on the Bogolyubov transformation. In particular, we study the case when the amplitude of the oscillation and also the coupling constants with the oscillating field are small to avoid the nonperturbative corrections from the broad parametric resonance. We derive the expressions for the distribution functions and the number densities of produced particles at the leading order of coupling constant. It is, however, found that these results fail to describe the exact particle production eventually due to the nonperturbative effects even if the coupling constants are small. We then introduce a simple method of handling such corrections, i.e., the time averaging method. It is shown that this method can successfully provide the evolution of the occupation numbers of the growing mode. Furthermore, we point out that the approximate results obtained by this method satisfy the exact scaling properties coming from the periodicity of the coherent oscillation.

DOI： 10.1143/PTP.124.293

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arXiv

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記述言語：英語   出版者・発行元：ELSEVIER SCIENCE BV  

We investigate baryogenesis in the nu MSM which is the Minimal Standard Model (MSM) extended by three right-handed neutrinos with Majorana masses being smaller than the weak scale. In this model three sterile neutrinos, which are almost right-handed states, play important roles in cosmology. The baryon asymmetry of the universe (BAU) is generated via mechanism through flavor oscillation between two sterile neutrinos N(2) and N(3) which are degenerate in masses. We consider the case when BAU is solely originated from the CP violating phases in the mixing matrix of active neutrinos, i.e., the Dirac phase delta and the Majorana phase eta, and study how BAU depends on these CP violating phases. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.ppnp.2009.12.056

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

We investigate baryogenesis in the nu MSM, which is the Minimal Standard Model (MSM) extended by three right-handed neutrinos with Majorana masses smaller than the weak scale. In this model the baryon asymmetry of the universe (BAU) is generated via flavour oscillation between right-handed neutrinos. We consider the case when BAU is solely originated from the CP violation in the mixing matrix of active neutrinos. We perform analytical and numerical estimations of the yield of BAU, and show how BAU depends on mixing angles and CP violating phases. It is found that the asymmetry in the inverted hierarchy for neutrino masses receives a suppression factor of about 4% comparing with the normal hierarchy case. It is, however, pointed out that, when theta(13) = 0 and theta(23) = pi/4, baryogenesis in the normal hierarchy becomes ineffective, and hence the inverted hierarchy case becomes significant to account for the present BAU. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physletb.2010.07.016

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arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER PHYSICAL SOC  

Seesaw models with a slightly broken lepton number symmetry can explain small neutrino masses, and allow for low-scale leptogenesis. We make a thorough analysis of leptogenesis within the simplest model with two right-handed (RH) neutrinos (or with N(3) decoupled). We obtain a semianalytical formula for the final asymmetry in both supersymmetric and nonsupersymmetric cases with a simple dependence on each parameter. The low-energy parameters factorize from the high-energy ones, and the high-energy phase must be nonzero. The role of the low-energy phases is carefully studied. Moreover, we find that the breaking parameter in the Yukawa coupling matrix must be relatively large, epsilon(h)greater than or similar to 10(-3) for normal and 10(-2) for inverted hierarchy. Therefore, leptogenesis in our simple model is incompatible with RH neutrino signals at future colliders or sizable lepton-flavor violation. The other breaking parameter, epsilon(M), which appears in the RH neutrino mass matrix, can be much smaller, and actually needs to be so in order to have low-scale leptogenesis.

DOI： 10.1103/PhysRevD.78.123527

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arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMERICAN PHYSICAL SOC  

We consider the minimal supersymmetric standard model (MSSM) extended by introducing three right-handed (s)neutrinos to account for neutrino masses in the oscillation experiments. Assuming that the neutrino masses are purely Dirac type, the lightest right-handed sneutrino nu(R) can be the lightest superparticle (LSP), which is a good candidate of cold dark matter (CDM) of the Universe. We study the possibility of realizing nu(R)-CDM, paying special attention to the production of nu(R) via decay of the next-to-lightest superparticle after its freeze-out time. It is shown that the late decay of the MSSM-LSP (the LSP among superparticles in the MSSM) can produce a sufficient amount of nu(R) to explain the observed dark matter density, and that the nu(R)-CDM scenario can be realized in a wide range of parameter space. We also consider the constraint on the decay of MSSM-LSP from the big bang nucleosynthesis; we found that the case with stau being the MSSM-LSP is severely constrained.

DOI： 10.1103/PhysRevD.75.065001

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arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：SPRINGER  

We determine the abundance of the lightest (dark matter) sterile neutrinos created in the Early Universe due to active-sterile neutrino transitions from the thermal plasma. Our starting point is the field-theoretic formula for the sterile neutrino production rate, derived in our previous work [JHEP 06( 2006) 053], which allows to systematically incorporate all relevant effects, and also to analyse various hadronic uncertainties. Our numerical results direr moderately from previous computations in the literature, and lead to an absolute upper bound on the mixing angles of the dark matter sterile neutrino. Comparing this bound with existing astrophysical X-ray constraints, we find that the Dodelson-Widrow scenario, which proposes sterile neutrinos generated by active-sterile neutrino transitions to be the sole source of dark matter, is only possible for sterile neutrino masses lighter than 3.5 keV (6 keV if all hadronic uncertainties are pushed in one direction and the most stringent X-ray bounds are relaxed by a factor of two). This upper bound may conflict with a lower bound from structure formation, but a definitive conclusion necessitates numerical simulations with the non-equilibrium momentum distribution function that we derive. If other production mechanisms are also operative, no upper bound on the sterile neutrino mass can be established.

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1126-6708/2007/01/091

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：AMER INST PHYSICS  

In supersymmetric models with right-handed neutrinos where the neutrino masses are purely Dirac-type, right-handed sneutrino is an interesting candidate of the lightest superparticle (LSP). Here we discuss the possibility that right-handed-sneutrino-LSP becomes dark matter of the universe.

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMERICAN PHYSICAL SOC  

We consider supersymmetric models with right-handed neutrinos where neutrino masses are purely Dirac-type. In this model, right-handed sneutrino can be the lightest supersymmetric particle and can be a viable candidate of cold dark matter of the universe. Right-handed sneutrinos are never thermalized in the early universe because of weakness of Yukawa interaction, but are effectively produced by decays of various superparticles. We show that the present mass density of right-handed sneutrino can be consistent with the observed dark matter density.

DOI： 10.1103/PhysRevD.73.051301

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arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：SPRINGER  

Sterile neutrinos with masses in the keV range are considered to be a viable candidate for warm dark matter. The rate of their production through active-sterile neutrino transitions peaks, however, at temperatures of the order of the QCD scale, which makes it difficult to estimate their relic abundance quantitatively, even if the mass of the sterile neutrino and its mixing angle were known. We derive here a relation, valid to all orders in the strong coupling constant, which expresses the production rate in terms of the spectral function associated with active neutrinos. The latter can in turn be expressed as a certain convolution of the spectral functions related to various mesonic current-current correlation functions, which are being actively studied in other physics contexts. In the naive weak coupling limit, the appropriate Boltzmann equations can be derived from our general formulae.

DOI： 10.1088/1126-6708/2006/06/053

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arXiv

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その他リンク： http://weblib.cern.ch/abstract?CERN-PH-TH-2006-085

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER PHYSICAL SOC  

Cosmological issues of the gravitino production by the decay of a heavy scalar field X are examined, assuming that the damped coherent oscillation of the scalar once dominated the energy of the universe. The coupling of the scalar field to a gravitino pair is estimated both in spontaneous and explicit supersymmetry breaking scenarios, with the result that it is proportional to the vacuum expectation value of the scalar field in general. Cosmological constraints depend on whether the gravitino is stable or not, and we study each case separately. For the unstable gravitino with M-3/2 similar to 100 GeV-10 TeV, we obtain not only the upper bound, but also the lower bound on the reheating temperature after the X decay, in order to retain the success of the big-bang nucleosynthesis. It is also shown that it severely constrains the decay rate into the gravitino pair. For the stable gravitino, similar but less stringent bounds are obtained to escape the overclosure by the gravitinos produced at the X decay. The requirement that the free-streaming effect of such gravitinos should not suppress the cosmic structures at small scales eliminates some regions in the parameter space, but still opens a new window for the gravitino warm dark matter. Implications of these results to inflation models are discussed. In particular, it is shown that modular inflation will face serious cosmological difficulty when the gravitino is unstable, whereas it can escape the constraints for the stable gravitino. A similar argument offers a solution to the cosmological moduli problem, in which the moduli is relatively heavy while the gravitino is light.

DOI： 10.1103/PhysRevD.74.023520

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

We explore the range of parameters for dark-matter sterile neutrinos in an extension of the Minimal Standard Model by three singlet fermions with masses below the electroweak scale (the nu MSM). This simple model can explain a wide range of phenomena, including neutrino oscillations, baryogenesis. the pulsar velocities, and the early reionization. The presence of two heavier sterile neutrinos and the possibility of entropy production in their decays broadens the allowed range of parameters for the dark-matter sterile neutrinos (or other types of dark matter, for example, the gravitino). In addition, the primordial production of dark matter sterile neutrinos allows to escape most of the constraints. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physletb.2006.05.067

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arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Cosmological issues of the gravitino production by the decay of a heavy scalar field X are examined, assuming that the damped coherent oscillation of the scalar once dominated the energy of the universe. The coupling of the scalar field to a gravitino pair is estimated both in spontaneous and explicit supersymmetry breaking scenarios, with the result that it is proportional to the vacuum expectation value of the scalar field in general. Cosmological constraints depend on whether the gravitino is stable or not, and we study each case separately. For the unstable gravitino with M3/2∼100GeV-10TeV, we obtain not only the upper bound, but also the lower bound on the reheating temperature after the X decay, in order to retain the success of the big-bang nucleosynthesis. It is also shown that it severely constrains the decay rate into the gravitino pair. For the stable gravitino, similar but less stringent bounds are obtained to escape the overclosure by the gravitinos produced at the X decay. The requirement that the free-streaming effect of such gravitinos should not suppress the cosmic structures at small scales eliminates some regions in the parameter space, but still opens a new window for the gravitino warm dark matter. Implications of these results to inflation models are discussed. In particular, it is shown that modular inflation will face serious cosmological difficulty when the gravitino is unstable, whereas it can escape the constraints for the stable gravitino. A similar argument offers a solution to the cosmological moduli problem, in which the moduli is relatively heavy while the gravitino is light. © 2006 The American Physical Society.

DOI： 10.1103/PhysRevD.74.023520

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.physletb.2005.09.070

Web of Science

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.physletb.2005.06.020

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMERICAN PHYSICAL SOC  

If inflaton couples very weakly to ordinary matter, the reheating temperature of the Universe can be lower than the electroweak scale. In this Letter we show that the late reheating occurs in a highly nonuniform way, within narrow areas along the jets produced by ordinary particles originated from inflaton decays. Depending on inflaton mass and decay constant, the initial temperature inside the lumps of the overheated plasma may be large enough to trigger the unsuppressed sphaleron processes with baryon number nonconservation. This allows for efficient local electroweak baryogenesis at reheating temperatures T(R)similar toO(10) GeV.

DOI： 10.1103/PhysRevLett.92.101303

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arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

We study anomalies of six-dimensional gauge theories compactified on orbifolds. In addition to the known bulk anomalies, brane anomalies appear on orbifold fixpoints in the case of chiral boundary conditions. At a fixpoint, where the bulk gauge group G is broken to a subgroup H, the non-Abelian G-anomaly in the bulk reduces to a H-anomaly which depends in a simple manner on the chiral boundary conditions. We illustrate this mechanism by means of a SO(10) GUT model. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0550-3213(02)00976-8

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arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

We study a supersymmetric SO(10) gauge theory in six dimensions compactified on an orbifold. Three sequential quarklepton families are localized at the three fixpoints where SO(10) is broken to its three GUT subgroups. Split bulk multiplets yield the Higgs doublets of the standard model and as additional states lepton doublets and down-quark singlets. The physical quarks and leptons are mixtures of brane and bulk states. The model naturally explains small quark mixings together with large lepton mixings in the charged current. A small hierarchy of neutrino masses is obtained due to the different down-quark and up-quark mass hierarchies. None of the usual GUT relations between fermion masses holds exactly. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0370-2693(03)00644-0

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arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

Lopsided structure in mass matrices of down quarks and leptons gives a simple explanation for the observed large angles of neutrino mixings. We realize such mass matrices by the Froggatt-Nielsen mechanism in the framework of supersymmetric SO(10) grand unified theory (GUT). It is shown that the model can reproduce the successful mass matrices which have been obtained in SU(5) models. Cosmological implication of the model is also discussed. We show that the hybrid inflation occurs naturally in the model and it offers non-thermal leptogenesis by decays of the next-to-lightest right-handed neutrinos. The present baryon asymmetry is explained by just the oscillation mass scale in the atmospheric neutrinos. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0370-2693(03)00611-7

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arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

We investigate a scheme for making leptogenesis by means of the (CP violating decays of the seesaw Majorana neutrinos proposed by Fukugita and Yanagida, However in order to avoid the washout of the produced lepton number we propose the production of the Majorana neutrinos to occur non-thermally and sufficiently late, After this time in consequence, the B - L (baryon minus lepton) quantum number becomes a good "accidental symmetry" protecting the asymmetry produced. This non-thermal leptogenesis at late time is realized by a boson decaying into the Majorana neutrinos with a long lifetime. Suggestively this boson could correspond to a scalar field which causes the cosmic inflation, the inflaton, and thus its decay means really the reheating of the Universe. We find that this mechanism works well even if the lightest Majorana neutrinos are not produced sufficiently or not present, and the decays of the heavier seesaw Majorana neutrino can be responsible to the baryon asymmetry in the present Universe, as we illustrate by the example of the family replicated gauge group model. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0550-3213(02)00934-3

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arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

The coset spaces E-8/SO(10) x H-F allow complex structures which can account for three quark-lepton generations including right-handed neutrinos. We show that in the context of supersynametric SO(10) gauge theories in 6 dimensions they also provide the Higgs fields which are needed to break the electroweak and B - L gauge symmetries, and to generate small neutrino masses via the seesaw mechanism. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0370-2693(02)02153-6

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arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/S0370-2693(01)01237-0

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arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

We study the breaking of a supersymmetric SO(10) GUT in 6 dimensions by orbifold compactification. In 4 dimensions we obtain a N = 1 supersymmetric theory with the standard model gauge group enlarged by an additional U(1) symmetry, The 4-dimensional gauge symmetry is obtained as intersection of the Pati-Salam and the Georgi-Glashow subgroups of SO(10). which appear as unbroken subgroups in the two 5-dimensional subspaces, respectively. The doublet-triplet splitting arises as in the recently discussed SU(5) GUTs in 5 dimensions. (C) 2001 Elsevier Science B.V. All fights reserved.

DOI： 10.1016/S0370-2693(01)01324-7

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arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

Inflation is terminated by a non-equilibrium process which finally leads to a thermal state. We study the onset of this transition in a class of hybrid inflation models. The exponential growth of tachyonic modes leads to decoherence and spinodal decomposition. We compute the decoherence time, the spinodal time, the size of the formed domains and the homogeneous classical fields within a single domain. (C) 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0370-2693(01)00623-2

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arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

We perform a detailed analysis on Affleck-Dine leptogenesis taking into account the thermal effects on the dynamics of the flat direction field (Formula presented) We find that an extremely small mass for the lightest neutrino (Formula presented) is required to produce enough lepton-number asymmetry to explain the baryon asymmetry in the present Universe. We impose here the reheating temperature after inflation (Formula presented) to be (Formula presented) to solve the cosmological gravitino problem. The required value of the neutrino mass seems to be very unlike the case since the recent SuperKamiokande experiments suggest the masses of the heavier two neutrinos (Formula presented) and (Formula presented) to be in a range of (Formula presented) We also propose a model to avoid this difficulty based on the Peccei-Quinn symmetry, where the required neutrino mass can be as large as (Formula presented). © 2000 The American Physical Society.

DOI： 10.1103/PhysRevD.62.123514

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arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

We investigate leptogenesis via decays of heavy Majorana neutrinos which are produced nonthermally in inflaton decays. We make a comprehensive study on leptogenesis assuming various supersymmetric (SUSY) models for hybrid, new, and topological inflations. For an estimation of the lepton asymmetry we adopt the Froggatt-Nielsen mechanism for mass matrices of quarks and leptons. We find that all of these models are successful in producing enough lepton asymmetry to explain the baryon number in the present universe. Here we impose low reheating temperatures such as (Formula presented) in order to suppress the abundance of gravitinos so they do not conflict with big-bang nucleosynthesis. Furthermore, we find that leptogenesis works very well even with (Formula presented) in the SUSY hybrid or new inflation model. It is known that such a reheating temperature is low enough to suppress the abundance of gravitinos of mass (Formula presented)–1 TeV. Thus, leptogenesis is fully consistent with big-bang nucleosynthesis in a wide region of the gravitino mass. © 2000 The American Physical Society.

DOI： 10.1103/PhysRevD.61.083512

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arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

In a large class of supersymmetric (SUSY) axion models the mass of the axino a (a fermionic superpartner of the axion) is predicted as m((a) over tilde) less than or similar to O(1) keV. Thus, the axino is the lightest SUSY particle (LSP). We pointed out that such a light axino provides a natural solution to the gravitino problem, if the gravitino is the next LSP. We derive a constraint on the reheating temperature T-R of inflation, T-R less than or similar to 10(15) GeV for the gravitino mass m(3/2) similar or equal to 100 GeV, which is much weaker than that obtained in the minimal SUSY standard model. (C) 2000 Published by Elsevier Science B.V.

DOI： 10.1016/S0370-2693(00)01209-0

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arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevD.61.027303

arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

We investigate the cosmological gravitino problem in gauge-mediated supersymmerry breaking models, where the gravitino becomes in general the lightest supersymmetric particle (LSP). In order to avoid the overclosure of the stable gravitino, the reheating temperature of inflation T-R should be low enough. Furthermore, if the gravitino moss is larger than about 100 MeV, the decay of the next-to-LSP (NLSP) into the gravitino may modify disastrously the abundances of the light elements predicted by the big-bang nucleosynthesis (BBN). We consider the case in which the lighter stau is the NLSP and derive cosmological constraints from the BBN on the stau NLSP decay. We obtain a lower bound on the mass of stau m(tau)over-bar-1, which is more stringent than the current experimental limit m(tau)over-bar-1 > 90 GeV for the gravitino mass region m(3/2) greater than or similar to 5 GeV. This lower bound, together with the overclosure constraint on the stable gravitino, gives an upper bound on T-R. We find that the reheating temperature can be as high as 10(9)-10(10) GeV for m(3/2) similar or equal to 5-100 GeV. (C) 2000 Published by Elsevier Science B.V.

DOI： 10.1016/S0370-2693(00)00959-X

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arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Recently we proposed a simple hadronic axion model within gauge-mediated supersymmetry breaking. In this paper we discuss various cosmological consequences of the model in great detail. Particular attention is paid to the saxion, a scalar partner of the axion, which is produced as a coherent oscillation in the early universe. We show that our model is cosmologically viable if the reheating temperature of inflation is sufficiently low. We also discuss the late decay of the saxion which gives a preferable power spectrum of the density fluctuation in the standard cold dark matter model when compared with observations. © 1999 The American Physical Society.

DOI： 10.1103/PhysRevD.59.125003

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arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier  

We investigate cosmological moduli problem in the gauge-mediated supersymmetry breaking (GMSB). A mini-inflation (oscillating inflation) takes place when a scalar field corresponding to the flat direction in GMSB oscillates along the logarithmic potential induced by the gauge-mediation mechanism. It is shown that this oscillating inflation can sufficiently dilute the relic abundance of the string moduli for some ranges of parameters in the GMSB models. © 1999 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0370-2693(99)00213-0

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arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

We study a leptogenesis via decays of heavy Majorana neutrinos produced non-thermally in inflation decays. We find that this scenario is fully consistent with existing supersymmetric inflation models such as for topological or for hybrid inflation and the Froggatt-Nielsen mechanism generating hierarchies in quark and lepton mass matrices. The reheating temperature T-R of inflation may be taken as low as T-R similar or equal to 10(8) GeV to avoid the cosmological gravitino problem. (C) 1999 Published by Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0370-2693(99)01020-5

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arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

In superstring theories, there exist various dilaton and modulus fields whose masses are expected to be of the order of the gravitino mass (Formula presented) These fields lead to serious cosmological difficulties, the so called “cosmological moduli problem,” because a large number of moduli particles are produced as the coherent oscillations after primordial inflation. We make a comprehensive study of whether the thermal inflation can solve the cosmological moduli problem in the whole modulus mass region (Formula presented) predicted by both hidden sector supersymmetry (SUSY) breaking and gauge-mediated SUSY breaking models. In particular, we take into account the primordial inflation model whose reheating temperature is so low that its reheating process finishes after the thermal inflation ends. We find that the above mass region (Formula presented) survives from various cosmological constraints in the presence of thermal inflation. © 1999 The American Physical Society.

DOI： 10.1103/PhysRevD.60.123509

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arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Thermal inflation is the most plausible mechanism that solves the cosmological moduli problem naturally. We discuss the relic abundance of a superheavy particle X in the presence of thermal inflation, assuming that its lifetime is longer than the age of the universe, and show that the long-lived particle X of mass (Formula presented) GeV may form a part of the dark matter in the present universe in a wide region of parameter space of the thermal inflation model. The superheavy dark matter of mass (Formula presented) GeV may be interesting in particular, since its decay may account for the observed ultrahigh-energy cosmic rays if the lifetime of the X particle is sufficiently long. © 1999 The American Physical Society.

DOI： 10.1103/PhysRevD.60.103518

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arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

A generic class of string theories predicts the existence of light moduli fields, and they are expected to have masses (Formula presented) comparable to the gravitino mass (Formula presented) which is in a range of (Formula presented) keV to 1 GeV in gauge-mediated supersymmetry breaking theories. Such light fields with weak interactions suppressed by the Planck scale cannot avoid some stringent cosmological constraints
that is, they suffer from “cosmological moduli problems.” We show that the total gravitino mass region (Formula presented) keV(Formula presented) GeV is excluded by the constraints even if we incorporate late-time mini-inflation (thermal inflation). However, a modification of the original thermal inflation model enables the region (Formula presented) keV(Formula presented) keV to survive the constraints. It is also stressed that the moduli can be dark matter in our universe for the mass region (Formula presented) keV(Formula presented) keV. © 1998 The American Physical Society.

DOI： 10.1103/PhysRevD.58.083509

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

A simple hadronic axion model is proposed in the framework of gauge-mediated supersymmetry breaking. Dynamics of Peccei-Quinn symmetry breaking is governed by supersymmetry breaking effects and the Peccei-Quinn breaking scale f(PQ) is inversely proportional to the gravitino mass. The gravitino mass range which corresponds to the axion window f(PQ) similar or equal to 10(9) GeV - 10(13) GeV lies in the region predicted by gauge-mediated supersymmetry breaking models. The model is also shown to be cosmologically viable. (C) 1998 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0370-2693(98)00890-9

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arXiv

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

We examine the x-ray spectrum from the decay of dark-matter moduli with mass (Formula presented) in particular, paying attention to the line spectrum from the moduli trapped in the halo of our galaxy. It is found that with the energy resolution of the current experiments (Formula presented) the line intensity is about twice as strong as that of the continuum spectrum from the moduli that spread in the whole universe. Therefore, in future experiments with higher energy resolutions it may be possible to detect such line photons. We also investigate the γ-ray spectrum emitted from the decay of the multi-GeV moduli. It is shown that the emitted photons may form a MeV bump in the γ-ray spectrum. We also find that if the modulus mass is of the order of 10 GeV, the emitted photons at the peak of the continuum spectrum lose their energy by scattering and the shape of the spectrum is significantly changed, which makes the constraint weaker than that obtained in previous works. © 1998 The American Physical Society.

DOI： 10.1103/PhysRevD.58.023507

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arXiv

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：Progress of Theoretical Physics  

Proceedings of YKIS '95

DOI： 10.1143/PTPS.123.151

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その他リンク： http://dl.ndl.go.jp/info:ndljp/pid/10884197

掲載種別：研究論文（学術雑誌）   出版者・発行元：American Physical Society (APS)  

DOI： 10.1103/physrevd.54.5698

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その他リンク： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevD.54.5698/fulltext

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

We calculate four-fermion decays of a Higgs boson via WW and/or ZZ intermediate states for Higgs masses below m(w). We examine models with a doubly-charged Higgs boson H++ and show that the four-fermion decay is the dominant mode for a wide range of parameter space. Existing searches for H++ in Z decays have not looked for this mode. We also derive four-fermion decay rate for a neutral Higgs boson.

DOI： 10.1016/0370-2693(94)01599-8

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arXiv

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Article

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Article

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Article

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Article

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Article

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Article

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記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Article

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出版者・発行元：IOP Publishing  

DOI： 10.1088/1742-6596/120/4/042006

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記述言語：英語   出版者・発行元：一般社団法人日本物理学会  

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掲載種別：機関テクニカルレポート，技術報告書，プレプリント等  

We discuss a supersymmetric unified model based on a product gauge group<br />
SU(5)\times SU(5)\times SU(5), where the gauge symmetry breaking is achieved<br />
without the adjoint or higher-dimensional Higgs field, and the doublet-triplet<br />
splitting in the Higgs masses is realized by the use of the discrete symmetry.<br />
In this article we present an explicit model for realistic fermion masses with<br />
the discrete symmetries Z_7\times Z_2. It is shown that all the observed masses<br />
and mixing angles for quarks and leptons, including neutrinos, are well<br />
described by the breaking of the symmetries imposed in the model. Especially,<br />
the maximal and large mixing angles in the atmospheric and solar neutrino<br />
oscillations are obtained as the most preferred values, and the typical value<br />
of the neutrino mixing element U_{e3} is 0.1-0.3. We also point out the<br />
non-trivial relations among the \mu-parameter for the Higgs mass, the charged<br />
fermion hierarchies, and the neutrino masses. These relations suggest that the<br />
scale of \mu is of order of the weak scale.

arXiv

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