Search

We demonstrate that the recent measurement of the anomalous magnetic moment of the muon and dark matter can be simultaneously explained within the minimal supersymmetric standard model. Dark matter is a mostly bino state, with the relic abundance obtained via coannihilations with either the sleptons or wino. The most interesting regions of parameter space will be tested by the next generation of dark matter direct detection experiments.

We present a supersymmetric solution to the strong CP problem based on spontaneous CP violation which simultaneously addresses the effects coming from supersymmetry breaking. The generated CP violating phase is communicated to the quark sector by interacting with a heavy quark a la Nelson-Barr. The Majorana mass of the right handed neutrinos is generated by interactions with the CP violating sector and so does not conserve CP. This gives the neutrino sector a nontrivial CP violating phase which can then generate the baryon asymmetry of the universe through leptogeneis. The problematic phase in the supersymmetry breaking parameters are suppressed by appealing to a particular gauge mediation model which naturally suppresses the phases of the tree-level gluino mass and Higgs bilinear masses. This suppression plus the fact that in gauge mediation all loop generated flavor and CP violation is of the minimal flavor violation variety allows for a complete and consistent solution to the strong CP problem.

Product group unification is an attractive alternative to simple grand unification. It solves the infamous doublet-triplet splitting problem and the dimension-5 proton decay problems without introducing any fine-tuning. Furthermore, the matter multiplets are still embedded into unified SU(5) representations. In this paper, we discuss proton decay of the simplest product group unification model based on SU(5)XU(2)_H . We find that the minimal setup of the model has already been excluded by dimension-6 proton decay. We also show that a simple extension of the model, with naturally generated SU(5) incomplete multiplets, can rectify this problem. We find that the proton lifetime will be in reach of coming experiments like DUNE and Hyper-K, when the mass of the incomplete multiplet is associated with the Peccei-Quinn symmetry breaking. In this case, the dark matter may be an admixture of the Wino LSP and the axion., Comment: 23 pages, 15 figures

The extension of the Standard Model by assuming $U(1{)}_{\mathrm{B}\text{\ensuremath{-}}\mathrm{L}}$ gauge symmetry is very well motivated since it naturally explains the presence of heavy right-handed neutrinos required to account for the small active neutrino masses via the seesaw mechanism and thermal leptogenesis. Traditionally, we introduce three right-handed neutrinos to cancel the $[U(1{)}_{\mathrm{B}\text{\ensuremath{-}}\mathrm{L}}{]}^{3}$ anomaly. However, it suffices to introduce two heavy right-handed neutrinos for these purposes and therefore we can replace one right-handed neutrino by new chiral fermions to cancel the $U(1{)}_{\mathrm{B}\text{\ensuremath{-}}\mathrm{L}}$ gauge anomaly. Then, one of the chiral fermions can naturally play a role of a dark matter candidate. In this paper, we demonstrate how this framework produces a dark matter candidate which can address the so-called ``core-cusp problem''. As one of the small-scale problems that the $\mathrm{\ensuremath{\Lambda}}$ cold dark matter paradigm encounters, it may imply an important clue for the nature of dark matter. One of resolutions among many is hypothesizing that sub-keV fermion dark matter halos in dwarf spheroidal galaxies are in a (quasi) degenerate configuration. We show how the degenerate sub-keV fermion dark matter candidate can be nonthermally originated in our model and thus can be consistent with the Lyman-$\ensuremath{\alpha}$ forest observation. Thereby, the small neutrino mass, baryon asymmetry, and the sub-keV dark matter become consequences of the broken B-L gauge symmetry.

We consider a general class of axion models, including the QCD and string axion, in which the PQ symmetry is broken before or during inflation. Assuming the axion is the dominant component of the dark matter, we discuss axion star formation in virialized dark minihalos around primordial black holes through gravitational Bose-Einstein condensation. We determine the conditions for minihalos to kinetically produce axion stars before galaxy formation. Today, we expect up to $\sim 10^{17}$ ($\sim 10^9$) axion stars in a radius of 100 parsecs around the Sun for the case of the QCD (string) axion., 7 pages, 3 figures. v2: updated towards version accepted in Physical Review D. v3: Some typos corrected

The perfect fit of the matter fields of the Standard Model into the SU(5) multiplets has strongly supported the idea of the grand unified theory (GUT) for decades. In this paper, we discuss a novel framework which explains why the Standard Model matter fields form the apparently complete SU(5) multiplets. In the new framework, the apparent matter unification inevitably results from chiral SU(5) gauge theory even if the quarks and leptons are not embedded into the common SU(5) multiplets. We call this class of models the “fake GUT.” The novel phenomenological prediction of the fake GUT is more variety of the nucleon decay modes than the conventional GUT, which reflects the rich structure of the origin of the matter fields.

We investigate the possibility that both dark matter and the long-standing discrepancy in the anomalous magnetic moment of the muon may be explained within the minimal supersymmetric standard model. In light of the stringent bounds from direct detection, we argue that the most promising viable scenarios have bino-like dark matter produced via either bino-wino or bino-slepton coannihilation. We find that the combination of next-generation direct detection experiments and the LHC will be able to probe much of the interesting parameter space; however a future high-energy collider is needed to comprehensively explore this scenario.

Primordial Black Hole (PBH) is one of the leading non-particle candidates for dark matter (DM). Although several observations severely constrain the amount of PBHs, it is recently pointed out that there is an uncertainty on the microlensing constraints below $\sim 10^{-10} M_\odot$ which was ignored originally but may weaken the constraints significantly. In this paper, facing this uncertainty, we investigate the possibility that PBHs can make up all DM in a broad mass spectrum. Moreover, we propose a concrete inflation model which can simultaneously produce PBHs for all DM in a broad mass spectrum around $\mathcal O(10^{-13}) M_\odot$ and PBHs for LIGO events in a sharp mass spectrum at $\mathcal O(10) M_\odot$., Comment: 11 pages, 5 figures, v2: published version

We propose a novel scenario to produce abundant primordial black holes (PBHs) in new inflation which is a second phase of a double inflation in the supergravity framework. In our model, some preinflation phase before the new inflation is assumed and it would be responsible for the primordial curvature perturbations on the cosmic microwave background scale, while the new inflation produces only the small scale perturbations. Our new inflation model has linear, quadratic, and cubic terms in its potential and PBH production corresponds with its flat inflection point. The linear term can be interpreted to come from a supersymmetry-breaking sector, and with this assumption, the vanishing cosmological constant condition after inflation and the flatness condition for the inflection point can be consistently satisfied.

Spontaneously broken supersymmetry (SUSY) and a vanishingly small cosmological constant imply that $R$ symmetry must be spontaneously broken at low energies. Based on this observation, we suppose that, in the sector responsible for low-energy $R$ symmetry breaking, a discrete $R$ symmetry remains preserved at high energies and only becomes dynamically broken at relatively late times in the cosmological evolution, i.e., after the dynamical breaking of SUSY. Prior to $R$ symmetry breaking, the Universe is then bound to be in a quasi--de Sitter phase---which offers a dynamical explanation for the occurrence of cosmic inflation. This scenario yields a new perspective on the interplay between SUSY breaking and inflation, which neatly fits into the paradigm of high-scale SUSY: inflation is driven by the SUSY-breaking vacuum energy density, while the chiral field responsible for SUSY breaking, the Polonyi field, serves as the inflaton. Because $R$ symmetry is broken only after inflation, slow-roll inflation is not spoiled by otherwise dangerous gravitational corrections in supergravity. We illustrate our idea by means of a concrete example, in which both SUSY and $R$ symmetry are broken by strong gauge dynamics and in which late-time $R$ symmetry breaking is triggered by a small inflaton field value. In this model, the scales of inflation and SUSY breaking are unified, the inflationary predictions are similar to those of F-term hybrid inflation in supergravity, reheating proceeds via gravitino decay at temperatures consistent with thermal leptogenesis, and the sparticle mass spectrum follows from pure gravity mediation. Dark matter consists of thermally produced winos with a mass in the TeV range.

We revisit the compatibility between chaotic inflation, which provides a natural solution to the initial condition problem, and the metastable electroweak vacuum, which is suggested by the results of the LHC and the current mass measurements of the top quark and Higgs boson. It is known that chaotic inflation poses a threat to the stability of the electroweak vacuum because it easily generates large Higgs fluctuations during inflation or preheating and triggers the catastrophic vacuum decay. In this paper, we propose a simple cosmological solution in which the vacuum is stabilized during chaotic inflation, preheating, and afterwards. This simple solution naturally predicts formation of primordial black holes. We find interesting parameter regions where the present dark matter density is provided by them. Also, the thermal leptogensis can be accommodated in our scenario.

TeV-scale seesaw mechanisms are interesting due to their potential testability at existing collider experiments. Herein we propose an ${\mathrm{E}}_{6}$-inspired model allowing a TeV-scale pseudo-Dirac singlet neutrino seesaw mechanism with naturally sizeable Yukawa couplings of $\mathcal{O}({10}^{\ensuremath{-}2})$. The model also contains new U(1) gauge interactions (and associated ${Z}^{\ensuremath{'}}$ bosons with which the singlet neutrinos can be produced at colliders), typically long-lived color triplet fermions, SU(2) doublet fermions, and a complex scalar---potentially all at the TeV scale. Additionally we identify three possible explanations for the 750 GeV diphoton excess.

In this paper, we revisit a visible heavy QCD axion model in light of the recent reports on the $750$ GeV diphoton resonance by the ATLAS and CMS experiments. In this model, the axion is made heavy with the help of the mirror copied sector of the Standard Model while the successful Peccei-Quinn mechanism is kept intact. We identify the $750$ GeV resonance as the scalar boson associated with spontaneous breaking of the Peccei-Quinn symmetry which mainly decays into a pair of the axions. We find that the mixings between the axion and $\eta$ and $\eta'$ play important roles in its decays and the resultant branching ratio into two photons. The axion decay length can be suitable for explaining the diphoton excess by the di-axion production when its decay constant $f_a \simeq 1$ TeV. We also find that our model allows multiple sets of the extra fermions without causing the domain wall problem, which is advantageous to explain the diphoton signal., Comment: 22 pages, 6 figures; a computational error is corrected

Although QCD axion models are widely studied as solutions to the strong CP problem, they generically confront severe fine-tuning problems to guarantee the anomalous PQ symmetry. In this letter, we propose a simple QCD axion model without any fine-tunings. We introduce an extra dimension and a pair of extra quarks living on two branes separately, which is also charged under a bulk Abelian gauge symmetry. We assume a monopole condensation on our brane at an intermediate scale, which implies that the extra quarks develop the chiral symmetry breaking and the PQ symmetry is broken. In contrast to the original Kim's model, our model explains the origin of the PQ symmetry thanks to the extra dimension and avoids the cosmological domain wall problem because of the chiral symmetry breaking in the Abelian gauge theory., Comment: 5 pages

The proximity of the Peccei-Quinn scale to the scale of supersymmetry breaking in models of pure gravity mediation hints at a common dynamical origin of these two scales. To demonstrate how to make such a connection manifest, we embed the Peccei-Quinn mechanism into the vector-like model of dynamical supersymmetry breaking a la IYIT. Here, we rely on the anomaly-free discrete Z4R symmetry required in models of pure gravity mediation to solve the mu problem to protect the Peccei-Quinn symmetry from the dangerous effect of higher-dimensional operators. This results in a rich phenomenology featuring a QCD axion with a decay constant of O(10^10) GeV and mixed WIMP/axion dark matter. In addition, exactly five pairs of extra 5 and 5* matter multiplets, directly coupled to the supersymmetry breaking sector and with masses close to the gravitino mass, m3/2 ~ 100 TeV, are needed to cancel the Z4R anomalies., 46 pages, 2 figures, 1 appendix

We pursue a class of visible axion models where the axion mass is enhanced by strong dynamics in a mirrored copy of the Standard Model in the line of the idea put forward by Rubakov. In particular, we examine the consistency of the models with laboratory, astrophysical, and cosmological constraints. As a result, viable parameter regions are found, where the mass of the axion is of $O(100)$ MeV or above while the Peccei-Quinn breaking scale is at around $10^{3\mbox{-}5}$ GeV., Comment: 12 pages, 3 figures

We propose a QCD axion model that avoids the cosmological domain wall problem, introducing a global SU(3)_f family symmetry to which we embed the unwanted PQ discrete symmetry. The spontaneous breaking of SU(3)_f and PQ symmetry predicts eight NG bosons as well as axion, all of which contribute to dark radiation in the Universe. The derivation from the standard model prediction of dark radiation can be observed by future observations of CMB fluctuations. Our model also predicts a sizable exotic kaon decay rate, which is marginally consistent with the present collider data and would be tested by future collider experiments., 16 pages

Gaugino mediation is very attractive since it is free from the serious avor problem in the supersymmetric standard model. We show that the observed Higgs boson mass at around 125 GeV and the anomaly of the muon g 2 can be easily explained in gaugino mediation models. It should be noted that no dangerous CP violating phases are generated in our framework. Furthermore, there are large parameter regions which can be tested not only at the planned International Linear Collider but also at the coming 13-14 TeV Large Hadron Collider.

Pure gravity mediation (PGM), with two free parameters, is a minimalistic approach to supergravity models, yet is capable of incorporating radiative electroweak symmetry breaking, a Higgs mass in agreement with the experimental measurement, without violating any phenomenological constraints. The model may also contain a viable dark matter candidate in the form of a wino. Here, we extend the minimal model by allowing the $\mu$-term to be a free parameter (equivalent to allowing the two Higgs soft masses, $m_1$ and $m_2$, to differ from other scalar masses) which are set by the gravitino mass. In particular, we examine the region of parameter space where $\mu \ll m_{3/2}$ in which case, the Higgsino becomes the lightest supersymmetric particle (LSP) and a dark matter candidate. We also consider a generalization of PGM which incorporates a Peccei-Quinn symmetry which determines the $\mu$-term dynamically. In this case, we show that the dark matter may either be in the form of an axion and/or a neutralino, and that the LSP may be either a wino, bino, or Higgsino., Comment: 24 pages, 13 Figures

Various theoretical and experimental considerations motivate models with high scale supersymmetry breaking. While such models may be difficult to test in colliders, we propose looking for signatures at much lower energies. We show that a keV line in the X-ray spectrum of galaxy clusters (such as the recently disputed 3.5 keV observation) can have its origin in a universal string axion coupled to a hidden supersymmetry breaking sector. A linear combination of the string axion and an additional axion in the hidden sector remains light, obtaining a mass of order 10 keV through supersymmetry breaking dynamics. In order to explain the X-ray line, the scale of supersymmetry breaking must be about $10^{11-12}$ GeV. This motivates high scale supersymmetry as in pure gravity mediation or minimal split supersymmetry and is consistent with all current limits. Since the axion mass is controlled by a dynamical mass scale, this mass can be much higher during inflation, avoiding isocurvature (and domain wall) problems associated with high scale inflation. In an appendix we present a mechanism for dilaton stabilization that additionally leads to $\mathcal{O}(1)$ modifications of the gaugino mass from anomaly mediation., Comment: 12 pages with 2 appendices; v2: updates to emphasize general results, other minor updates, matches published version

Chaotic inflation based on a simple monomial scalar potential, $V(\ensuremath{\phi})\ensuremath{\propto}{\ensuremath{\phi}}^{p}$, is an attractive large-field model of inflation capable of generating a sizable tensor-to-scalar ratio $r$. Therefore, assuming that future cosmic microwave background observations will confirm the large $r$ value reported by BICEP2, it is important to determine what kind of dynamical mechanism could possibly endow the inflaton field with such a simple effective potential. In this paper, we answer this question in the context of field theory, i.e. in the framework of dynamical chaotic inflation, where strongly interacting supersymmetric gauge dynamics around the scale of grand unification dynamically generate a fractional power-law potential via the quantum effect of dimensional transmutation. In constructing explicit models, we significantly extend our previous work, as we now consider a large variety of possible underlying gauge dynamics and relax our conditions on the field content of the model. This allows us to realize almost arbitrary rational values for the power $p$ in the inflaton potential. The present paper may hence be regarded as a first step toward a more complete theory of dynamical chaotic inflation.

We reexamine the models with gauge mediation in view of the minimality. As a result, we arrive at a very simple model of direct gauge mediation which does not suffer from the flavor problems nor the CP problems. We show that the parameter space which is consistent with the Higgs boson mass at around 126 GeV can be tested through the stable stau searches at the 14TeV run of the LHC. The gravitino is a viable candidate for a dark matter. We also give a short discussion on a possible connection of our model to the recently discovered X-ray line signal at 3.5 keV in the XMM Newton X-ray observatory data., Comment: 20 pages, 6 figures

In supersymmetric theories, the $R$ symmetry plays a unique role in suppressing a constant term in the superpotential. In single chiral field models of spontaneous breaking of a discrete $R$ symmetry, an $R$-breaking field can be a good candidate for an inflaton in new inflation models. In this paper, we revisit the compatibility of the single-field $R$-breaking new inflation model with the results of the Planck experiment. As a result, we find that the model predicts a lower limit on the gravitino mass, ${m}_{3/2}gO(100)\text{ }\text{ }\mathrm{TeV}$, assuming that the $R$-symmetry breaking is dominantly induced by the inflaton and the inflaton dynamics is not affected by the supersymmetry-breaking sector, which can be guaranteed by symmetry or compositeness of the supersymmetry-breaking sector. This lower limit is consistent with the observed Higgs mass of 126 GeV when the masses of the top squarks are of order the gravitino mass scale. We also show that the baryon asymmetry of the Universe as well as the observed dark matter density can be consistently explained along with the $R$-breaking new inflation model, assuming leptogenesis and that the wino is the lightest supersymmetric particle.

The dilaton field in string theories (if exists) is expected to have a mass of the order of the gravitino mass $m_{3/2}$ which is in a range of $10^{-2}$keV--1GeV in gauge-mediated supersymmetry breaking models. If it is the case, the cosmic energy density of coherent dilaton oscillation easily exceeds the critical density of the present universe. We show that even if this problem is solved by a late-time entropy production (thermal inflation) a stringent constraint on the energy density of the dilaton oscillation is derived from experimental upperbounds on the cosmic X($\gamma$)-ray backgrounds. This excludes an interesting mass region, $500keV \lesssim m_{3/2} \lesssim 1GeV$, in gauge-mediated supersymmetry breaking models., Comment: 13 pages (RevTex file including one figure, use psfig), revised version to be published in Physical Review Letters

We point out that if the Peccei-Quinn symmetry breaking scale F{sub a} is in a range of the hadronic axion window (F{sub a}{approximately}10{sup 6} GeV), the ee{gamma}{gamma}+E/{sub T} event in the CDF experiment can be naturally explained by a no-scale supergravity model with a light axino. We also stress that the hadronic axion window still survives the intergalactic photon search, since a large entropy production due to the decay of Polonyi field yields a substantial dilution of the cosmic axion density. {copyright} {ital 1997} {ital The American Physical Society}

The axion solution to the strong $CP$ problem calls for an explanation as to why the Lagrangian should be invariant under the global Peccei-Quinn (PQ) symmetry, $U(1{)}_{\mathrm{PQ}}$, to such a high degree of accuracy. In this paper, we point out that the $U(1{)}_{\mathrm{PQ}}$ can indeed survive as an accidental symmetry in the low-energy effective theory, if the standard model gauge group is supplemented by a gauged and discrete $R$ symmetry, ${Z}_{N}^{R}$, forbidding all dangerous operators that explicitly break the Peccei-Quinn symmetry. In contrast to similar approaches, the requirement that the ${Z}_{N}^{R}$ symmetry be anomaly-free forces us, in general, to extend the supersymmetric standard model by new matter multiplets. Surprisingly, we find a large landscape of viable scenarios that all individually fulfill the current experimental constraints on the QCD vacuum angle as well as on the axion decay constant. In particular, choosing the number of additional multiplets appropriately, the order $N$ of the ${Z}_{N}^{R}$ symmetry can take any integer value larger than 2. This has interesting consequences with respect to possible solutions of the $\ensuremath{\mu}$ problem, collider searches for vectorlike quarks and axion dark matter.

Here we give a broad overview of the more natural spectra allowed by the LHC when $UDD$ $R$-parity violation is allowed. Because $R$-parity violation removes the missing energy signals in colliders, the experimental constraints on the gluino, stops, sbottoms, and Higgsinos are relatively mild. We also show that $UDD$ $R$-parity violation and lepton number conservation can be made consistent with grand unification. This feat is achieved through the product unification, $SU(5)\ifmmode\times\else\texttimes\fi{}U(3)$. In this model, mixing of the standard model quarks with additional quarklike particles charged under the $U(3)$ generate a $UDD$ $R$-parity violating operator. Furthermore, these models are also capable of generating a ``natural'' spectra. The emergence of these more natural low-scale spectra relies heavily on the fact that the gaugino masses are nonuniversal, a natural consequence of product unification.

We propose a unified model of elementary particles based on a supersymmetric SO(10){sub GUT}{times} SO(6){sub {ital H}} gauge theory. This model completely achieves natural unification of the strong and electroweak interactions without any fine tunings. The masslessness of Higgs doublets is guaranteed by a chiral U(1){sub {ital A}} symmetry. On the other hand, the Higgs triplets have a GUT-scale mass invariant under the chiral U(1){sub {ital A}}. {copyright} {ital 1996 The American Physical Society.}

Supersymmetric theories which can allow for a 125 GeV Higgs mass and also solve the naturalness and susy flavor problems now require a fair degree of complexity. Here we consider the simplest possibility for supersymmetry near the weak scale, but with the requirement of naturalness dropped. In "pure gravity mediation", all supersymmetric particles except for the gauginos lie at tens to thousands of TeV, with the gauginos obtaining loop suppressed masses automatically by anomaly mediation and higgsino threshold corrections. The gauginos are the lightest superpartners, and we investigate the current collider constraints on their masses, as well as the future reach of the LHC. We consider gluino pair production with a jets + missing energy signature, as well as events with disappearing charged tracks caused by charged winos decaying into their neutral partners. We show that presently, gluino masses less than about 1 TeV and wino masses less than about 300 GeV are excluded, and that the 14 TeV LHC can probe gluino masses up to about 2 TeV and wino masses up to 1 TeV.

Recently, the ATLAS and CMS collaborations reported exciting hints of a Standard Model-like Higgs boson with a mass around 125 GeV. Such a Higgs boson mass can be easily obtained in the minimal supersymmetric Standard Model based on the \pure gravity mediation model" where the sfermion masses and the Higgs mass parameters are in tens to hundreds TeV range while the gauginos are in the hundreds GeV to TeV range. In this paper, we discuss detalis of the gaugino mass spectrum in the pure gravity mediation model. We also discuss the signals of the model at the current and future experiments such as cosmic ray observations and the LHC experiments. In particular, we show that the parameter space which is consistent with the thermal leptogenesis can be fully surveyed experimentally in the foreseeable future.

Recently, the ATLAS and CMS collaborations reported exciting hints of a Standard Model-like Higgs boson with a mass around 125GeV. A Higgs boson this heavy is difficult to realize in conventional models of gauge mediation. Here we revisit the lightest Higgs boson mass in "more generic gauge mediation," where the Higgs doublets mix with the messenger doublets. We show that a Higgs boson mass around 125GeV can be realized in more generic gauge mediation models, even for a relatively light gluino mass ~1TeV. We also show that the muon anomalous magnetic moment can be within 1sigma of the experimental value for these models, even when the Higgs boson is relatively heavy. We also discuss the LHC constraints and the prospects of discovery., 28 pages, 7 figures. Corrections and references are added

One of the solutions to the cosmological Polonyi problem is to introduce a large coupling between the Polonyi field and the inflaton so that the Polonyi field adiabatically tracks the temporal minimum of the potential. We study general conditions for the adiabatic suppression mechanism to work, and find that a non-negligible amount of the Polonyi field is induced in the form of coherent oscillations at the end of inflation. In the case of low reheating temperature, this contribution is so small that it does not cause cosmological problems. On the other hand, this contribution may be significant for a relatively high reheating temperature and we still need some amount of tuning in order to avoid the Polonyi problem. We also point out that Polonyi particles produced from thermal plasma pose a severe constraint on the reheating temperature. Furthermore, we extend the original framework to include enhanced couplings of the Polonyi field with the visible particles as well as with itself, and derive upper bounds on the reheating temperature after inflation. We also investigate the adiabatic solution to the cosmological moduli problem in gauge and anomaly mediation.

We present a model of chaotic inflation driven by the superpartner of the right-handed neutrino ([ital [tilde N]][sub [ital R]]). This model gives the correct magnitude of the density perturbation observed by the Cosmic Background Explorer satellite with a right-handed neutrino mass [congruent]10[sup 13] GeV, which is also preferred by the Mikheyev-Smirnov-Wolfenstein solution to the solar neutrino problem. The reheating process is the dacay of the coherently oscillating [ital [tilde N]][sub [ital R]]. This decay process also generates lepton asymmetry via [ital CP] violation, which will be converted to baryon asymmetry thanks to the electroweak anomaly. This model can incorporate the [tau]-neutrino mass [congruent]10 eV.

Scenarios where gravitinos with GeV masses make up dark matter are known to be in tension with high reheating temperatures, as required by e.g. thermal leptogenesis. This tension comes from the longevity of the NLSPs, which can destroy the successful predictions of the standard primordial nucleosynthesis. However, a small violation of matter parity can open new decay channels for the NLSP, avoiding the BBN problems, while being compatible with experimental cosmic-ray constraints. In this paper, we propose a model where matter parity, which we assume to be embedded in the U(1)_{B-L} gauge symmetry, is broken dynamically in a hidden sector at low scales. This can naturally explain the smallness of the matter parity breaking in the visible sector. We discuss the dynamics of the corresponding pseudo Nambu--Goldstone modes of B-L breaking in the hidden sector, and we comment on typical cosmic-ray and collider signatures in our model., 20 pages, 1 figure, 1 table

We show that the gravitino-overproduction problem is prevalent among inflation models in supergravity. An inflaton field $\ensuremath{\phi}$ generically acquires (effective) nonvanishing auxiliary field ${\mathcal{G}}_{\ensuremath{\Phi}}^{(\mathrm{eff})}$, if the K\"ahler potential is nonminimal. The inflaton field then decays into a pair of the gravitinos. We extensively study the cosmological constraints on ${\mathcal{G}}_{\ensuremath{\Phi}}^{(\mathrm{eff})}$ for a wide range of the gravitino mass. For many inflation models we explicitly estimate ${\mathcal{G}}_{\ensuremath{\Phi}}^{(\mathrm{eff})}$, and show that the gravitino-overproduction problem severely constrains the inflation models, unless such an interaction as $K=\ensuremath{\kappa}/2|\ensuremath{\phi}{|}^{2}{z}^{2}+\mathrm{H}.\mathrm{c}.$ is suppressed (here $z$ is the field responsible for the supersymmetry breaking). We find that many of them are already excluded or on the verge of, if $\ensuremath{\kappa}\ensuremath{\sim}O(1)$.

We provide, in a framework of vectorlike gauge theories, concrete models for conformal sequestering of dynamical supersymmetry (SUSY) breaking in the hidden sector. If the sequestering is sufficiently strong, anomaly mediation of the SUSY breaking may give dominant contributions to the mass spectrum of SUSY standard model particles, leading to negative slepton masses squared. Thus, we also consider a model with gravitational gauge mediation to circumvent the tachyonic slepton problem in pure anomaly-mediation models.

Minimal supergravity mediation of supersymmetry breaking has attracted much attention due to its simplicity, which leads to its predictive power. We consider how Nature possibly realizes minimal supergravity through inflationary selection of the theory. Minimality is impressively consistent with the present observational bounds and it might be tested with the aid of low-energy soft parameters obtained in future experiments., 18 pages, 5 figures

We investigate in detail leptogenesis by the decay of a coherent right-handed sneutrino $\~N$ having dominated the energy density of the early universe, which was originally proposed by two of the authors (H.M. and T.Y.). Once the $\~N$ dominant universe is realized, the amount of generated lepton asymmetry (and hence baryon asymmetry) is determined only by the properties of the right-handed neutrino, regardless of the history before it dominates the universe. Moreover, thanks to the entropy production by the decay of the right-handed sneutrino, thermally produced relics are sufficiently diluted. In particular, the cosmological gravitino problem can be avoided even when the reheating temperature of inflation is higher than ${10}^{10}\mathrm{GeV},$ in a wide range of the gravitino mass ${m}_{3/2}\ensuremath{\simeq}10\mathrm{MeV}\char21{}100\mathrm{TeV}.$ If the gravitino mass is in the range ${m}_{3/2}\ensuremath{\simeq}10\mathrm{MeV}\char21{}1\mathrm{}\mathrm{GeV}$ as in some gauge-mediated supersymmetry breaking models, the dark matter in our Universe can be dominantly composed of the gravitino. The quantum fluctuation of $\~N$ during inflation causes an isocurvature fluctuation which may be detectable in the future.

We study the supersymmetric leptogenesis via the ${\mathrm{LH}}_{u}$ flat direction with a gauged ${U(1)}_{B\ensuremath{-}L}$ symmetry. We find that the resultant baryon asymmetry is enhanced compared with the case without a gauged ${U(1)}_{B\ensuremath{-}L}$ symmetry. The baryon asymmetry is proportional to the reheating temperature of inflation, but it is independent of the gravitino mass. If high reheating temperatures of inflation ${T}_{R}\ensuremath{\sim}{10}^{10}\mathrm{GeV}$ are available, the mass of the lightest neutrino, ${m}_{\ensuremath{\nu}1}\ensuremath{\sim}{10}^{\ensuremath{-}4}\mathrm{eV},$ is small enough to explain the baryon asymmetry in the present universe. Furthermore, the gravitino mass independence of the produced baryon asymmetry allows us to explain the present baryon asymmetry even in low energy supersymmetry breaking scenarios such as gauge-mediation models. Our leptogenesis scenario is also very special in the sense that it is completely free from the serious Q-ball formation problem.

We briefly review the present status of Affleck-Dine baryo/leptogenesis scenarios in the minimal supersymmetric standard model (MSSM) in the context of the gravity-mediated SUSY breaking, and show that there is a serious cosmological problem in the Affleck-Dine mechanism. That is, the late decay of the associated large Q-balls leads to the over production of the lightest supersymmetric particles. Then, we point out that the minimal extension of the MSSM by introducing a gauged $U(1)_{B-L}$ symmetry naturally solves this problem. Here, the breaking scale of the $U(1)_{B-L}$ can be determined quite independently of the reheating temperature from the required baryon asymmetry. It is extremely interesting that the obtained scale of the $U(1)_{B-L}$ breaking is well consistent with the one suggested from the seesaw mechanism to explain the recent neutrino-oscillation experiments. We consider that the present scenario provides a new determination of the $U(1)_{B-L}$ breaking scale fully independent of the neutrino masses. We also comment on viability of the present scenario in anomaly-mediated SUSY breaking models.

We investigate the leptogenesis via decays of heavy Majorana neutrinos which are produced non-thermally in inflaton decays. We make a comprehensive study on the 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 to produce the lepton asymmetry enough to explain the baryon number in the present universe. Here we impose low reheating temperatures such as $T_R \lesssim 10^8$ GeV in order to suppress the abundance of gravitinos not to conflict with the big-bang nucleosynthesis. Furthermore, we find that the leptogenesis works very well even with $T_R \simeq 10^{6}$ GeV 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 $m_{3/2} \simeq 100$ GeV--1 TeV. Thus, the leptogenesis is fully consistent with the big-bang nucleosynthesis in a wide region of the gravitino mass., 42 pages, 17 figures

The cosmological implication of a double inflation model with hybrid + new inflations in supergravity is studied. The hybrid inflation drives an inflaton for new inflation close to the origin through supergravity effects and new inflation naturally occurs. If the total e-fold number of new inflation is smaller than $\sim 60$, both inflations produce cosmologically relevant density fluctuations. Both cluster abundances and galaxy distributions provide strong constraints on the parameters in the double inflation model assuming $\Omega_0=1$ standard cold dark matter scenario. The future satellite experiments to measure the angular power spectrum of the cosmic microwave background will make a precise determination of the model parameters possible., Comment: 19 pages (RevTeX file)

Superheavy particles of masses $\simeq 10^{13}-10^{14} GeV$ with lifetimes $\simeq 10^{10}-10^{22} years$ are very interesting, since their decays may account for the ultra-high energy (UHE) cosmic rays discovered beyond the Greisen-Zatsepin-Kuzmin cut-off energy $E \sim 5 \times 10^{10} GeV$. We show that the presence of such long-lived superheavy particles is a generic prediction of QCD-like SU(N_c) gauge theories with N_f flavors of quarks and antiquarks and the large number of colors N_c. We construct explicit models based on supersymmetric SU(N_c) gauge theories and show that if the dynamical scale $\Lambda \simeq 10^{13}-10^{14} GeV$ and N_c = 6-10 the lightest composite baryons have the desired masses and lifetimes to explain the UHE cosmic rays. Interesting is that in these models the gaugino condensation necessarily occurs and hence these models may play a role of so-called hidden sector for supersymmetry breaking in supergravity., Comment: 13 pages, Latex

The thermal inflation is the most plausible mechanism that solves the cosmological moduli problem naturally. We discuss relic abundance of superheavy particle $X$ in the presence of the thermal inflation assuming that its lifetime is longer than the age of the universe, and show that the long-lived particle $X$ of mass $10^{12}$--$10^{14}$ 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 $\sim 10^{13}$ GeV may be interesting in particular, since its decay may account for the observed ultra high-energy cosmic rays if the lifetime of the $X$ particle is sufficiently long., Comment: 13 pages (RevTex file) including 8 figures, revised version to be published in Physical Review D

We find a grand unified SO(10) model which accommodates the bimaximal neutrino mixing for vacuum-oscillation solutions to the atmospheric and solar neutrino problems. This model maintains the original SO(10) mass relation between neutrino and up-type quark masses ${m}_{{\ensuremath{\nu}}_{2}}{/m}_{{\ensuremath{\nu}}_{3}}\ensuremath{\sim}{(m}_{c}{/m}_{t}{)}^{2}.$

A generic class of string theories predicts the existence of light moduli fields, and they are expected to have masses $m_\phi$ comparable to the gravitino mass $m_{3/2}$ which is in a range of $10^{-2}$keV--1GeV in gauge-mediated supersymmetry breaking theories. Such light fields with weak interactions suppressed by the Planck scale can not avoid some stringent cosmological constraints, that is, they suffer from `cosmological moduli problems'. We show that all the gravitino mass region $10^{-2}$keV $\lesssim m_{3/2} \lesssim$ 1GeV is excluded by the constraints even if we incorporate a late-time mini-inflation (thermal inflation). However, a modification of the original thermal inflation model enables the region $10^{-2}$keV $\lesssim m_{3/2} \lesssim$ 500keV to survive the constraints. It is also stressed that the moduli can be dark matter in our universe for the mass region $10^{-2}$keV $\lesssim m_\phi \lesssim$ 100keV., Comment: A few changes in section IV and V

We point out that the baryon-number asymmetry in the Universe is erased by the sphaleron effect just below the electroweak phase transition irrespective of the primordial baryon- and lepton-number asymmetry, if there exists a Majorana-type interaction. The requirement to avoid this happening leads to the condition that ${m}_{\ensuremath{\nu}} (\mathrm{Majorana})l50$ keV for all species of neutrions, regardless of whether or not neutrinos are stable.

Cosmological baryon excess is used to probe how the left-right symmetry should be broken in a basically symmetric grand unified theory. In the SO(10) model, the contribution from an intermediate state containing the chiral partner of a light ordinary neutrino cancels much of the usual baryon excess produced by a heavy-Higgs-boson decay unless the partner's mass is \ensuremath{\gtrsim}${10}^{10}$ GeV. A mechanism of soft $\mathrm{CP}$ violation is also mentioned.

In the Weinberg-Salam model with vanishing mixing angle ${\ensuremath{\theta}}_{W}$=0, the static minimum-energy path is obtained within the general spherically symmetric ansatz, which connects a vacuum to the sphaleron of Klinkhamer and Manton. The physical significance of the path is discussed in connection with a possible baryon-number-violating effect at high temperature.