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Motoi Endo

Publications and source records attributed to Motoi Endo.

At least 91 records · Page 5Linked to original sources
arXiv2007

Dark Matter in Gauge Mediated Supersymmetry Breaking using Metastable Vacua

We point out that, in a class of gauge mediation models using metastable supersymmetry breaking vacua, the minimum of the supersymmetry breaking field in the early universe is dynamically deviated from the one in the low energy. The deviation induces coherent oscillations of the supersymmetry breaking field, which decays into the gravitinos. For certain parameters, it can produce a right amount of the gravitinos to account for the observed dark matter.

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arXiv2007

Inflaton Decay in Supergravity

We discuss inflaton decay in supergravity, taking account of the gravitational effects. It is shown that, if the inflaton has a nonzero vacuum expectation value, it generically couples to any matter fields that appear in the superpotential at the tree level, and to any gauge sectors through anomalies in the supergravity. Through these processes, the inflaton generically decays into the supersymmetry breaking sector, producing many gravitinos. The inflaton also directly decays into a pair of the gravitinos. We derive constraints on both inflation models and supersymmetry breaking scenarios for avoiding overproduction of the gravitinos. Furthermore, the inflaton naturally decays into the visible sector via the top Yukawa coupling and SU(3)_C gauge interactions.

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arXiv2007

Retrofitted Gravity Mediation without the Gravitino-overproduction Problem

We propose a retrofitted gravity mediation model which alleviates the gravitino overproduction from decays of an inflaton and a supersymmetry breaking field. In the model, we introduce an approximate U(1) symmetry under which the supersymmetry breaking field is charged, although it is broken by a mass term of messenger fields to generate gaugino masses of order the weak scale. In a low-scale inflation model, we find regions in which the gravitino overproduction problem is avoided.

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arXiv2007

The Decay of the Inflaton in No-scale Supergravity

We study the decay of the inflaton in no-scale supergravity and show that decay due to the gravitational interactions through supergravity effects is highly suppressed relative to the case in minimal supergravity or models with a generic Kahler potential. We also show that decay to gravitinos is suppressed. We demonstrate that decay and sufficient reheating are possible with the introduction of a non-trivial gauge kinetic term. This channel may be dominant in no-scale supergravity, yet yields a re-heating temperature which is low enough to avoid the gravitino problem while high enough for Big Bang Nucleosynthesis and baryogenesis.

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arXiv2007

Anomaly-Induced Inflaton Decay and Gravitino-Overproduction Problem

We point out that the inflaton spontaneously decays into any gauge bosons and gauginos via the super-Weyl, Kahler and sigma-model anomalies in supergravity, once the inflaton acquires a non-vanishing vacuum expectation value. In particular, in the dynamical supersymmetry breaking scenarios, the inflaton necessarily decays into the supersymmetry breaking sector, if the inflaton mass is larger than the dynamical scale. This generically causes the overproduction of the gravitinos, which severely constrains the inflation models.

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arXiv2006

Spontaneous Non-thermal Leptogenesis in High-scale Inflation Models

We argue that a non-thermal leptogenesis occurs spontaneously, without direct couplings of the inflaton with right-handed neutrinos, in a wide class of high-scale inflation models such as the chaotic and hybrid inflation. It is only a finite vacuum expectation value of the inflaton, or more precisely, a linear term in the Kahler potential, that is a prerequisite for the spontaneous non-thermal leptogenesis. To exemplify how it works, we show that a chaotic inflation model in supergravity naturally produces a right amount of baryon asymmetry via the spontaneous non-thermal leptogenesis. We also discuss the gravitino production from the inflaton.

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arXiv2006

Inflaton Decay through Supergravity Effects

We point out that supergravity effects enable the inflaton to decay into all matter fields, including the visible and the supersymmetry breaking sectors, once the inflaton acquires a non-vanishing vacuum expectation value. The new decay processes have great impacts on cosmology; the reheating temperature is bounded below; the gravitinos are produced by the inflaton decay in a broad class of the dynamical supersymmetry breaking models. We derive the bounds on the inflaton mass and the vacuum expectation value, which severely constrain high-scale inflations such as the hybrid and chaotic inflation models.

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arXiv2006

Constraint on Right-Handed Squark Mixings from B_s - B_sbar Mass Difference

We point out that the right-handed squark mixings can sizably enhance SUSY contributions to Delta M_s by taking into account renormalization group effects via the CKM matrix. The recent result of Delta M_s from the D0 experiment at the Tevatron thus implies a strong constraint on the right-handed mixings.

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arXiv2006

Moduli/Inflaton Mixing with Supersymmetry Breaking Field

A heavy scalar field such as moduli or an inflaton generally mixes with a field responsible for the supersymmetry breaking. We study the scalar decay into the standard model particles and their superpartners, gravitinos, and the supersymmetry breaking sector, particularly paying attention to decay modes that proceed via the mixing between the scalar and the supersymmetry breaking field. The impacts of the new decay processes on cosmological scenarios are also discussed; the modulus field generically produces too much gravitinos, and most of the inflation models tend to result in too high reheating temperature and/or gravitino overproduction.

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arXiv2006

Non-thermal Production of Dark Matter from Late-Decaying Scalar Field at Intermediate Scale

We examine non-thermal dark matter production from a late-decaying scalar field, with a particular attention on non-renormalizable operators of D=5 through which the scalar field decays into the standard model particles and their superpartners. We show that almost the same number of superparticles as that of particles are generally produced from the decay. To avoid the gravitino overproduction problem, the decay is favored to proceed via interactions with an intermediate cut-off scale M << M_P. This should be contrasted to the conventional scenario using the modulus decay. The bosonic supersymmetry partner of the axion, i.e., saxion, is proposed as a natural candidate for such late-decaying scalar fields. We find that a right amount of the wino/higgsino dark matter with a mass of O(100) GeV is obtained for the saxion mass around the weak scale and axion decay constant, F_A = O(10^{9-12}) GeV.

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arXiv2006

Moduli-Induced Gravitino Problem

We investigate the cosmological moduli problem by studying a modulus decay in detail and find that the branching ratio of the gravitino production is generically of O(0.01-1), which causes another cosmological disaster. Consequently, the cosmological moduli problem cannot be solved simply by making the modulus mass heavier than 100 TeV. We also illustrate our results by explicitly calculating the branching ratio into the gravitinos in the mixed modulus--anomaly/KKLT- and racetrack-type models.

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arXiv2005

Bottom-Up Approach to Moduli Dynamics in Heavy Gravitino Scenario : Superpotential, Soft Terms and Sparticle Mass Spectrum

The physics of moduli fields is examined in the scenario where the gravitino is relatively heavy with mass of order 10 TeV, which is favored in view of the severe gravitino problem. The form of the moduli superpotential is shown to be determined, if one imposes a phenomenological requirement that no physical CP phase arise in gaugino masses from conformal anomaly mediation. This bottom-up approach allows only two types of superpotential, each of which can have its origins in a fundamental underlying theory such as superstring. One superpotential is the sum of an exponential and a constant, which is identical to that obtained by Kachru et al (KKLT), and the other is the racetrack superpotential with two exponentials. The general form of soft supersymmetry breaking masses is derived, and the pattern of the superparticle mass spectrum in the minimal supersymmetric standard model is discussed with the KKLT-type superpotential. It is shown that the moduli mediation and the anomaly mediation make comparable contributions to the soft masses. At the weak scale, the gaugino masses are rather degenerate compared to the minimal supergravity, which bring characteristic features on the superparticle masses. In particular, the lightest neutralino, which often constitutes the lightest superparticle and thus a dark matter candidate, is a considerable admixture of gauginos and higgsinos. We also find a small mass hierarchy among the moduli, gravitino, and superpartners of the standard-model fields. Cosmological implications of the scenario are briefly described.

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arXiv2004

Recent Measurements of CP Asymmetries of B \to ϕK^0 and B \to η' K_S at B-factories Suggest New CP Violation in Left-Handed Squark Mixing

Recent results on the mixing-induced CP asymmetries of B \to ϕK^0 and B \to η' K_S measured at B-factories appear to indicate discrepancies from the Standard Model expectation. Explanation of this possible anomaly is given in the context of supersymmetric extension of the Standard Model. It is shown that the present data, if the average of two experiments is taken, implies additional CP violation appearing in the generation mixing of left-handed squarks rather than that of right-handed ones. This explanation is argued to disfavor many mediation mechanisms of supersymmetry breaking, including minimal supergravity, because renormalization group effects via Yukawa interaction are unlikely to generate the desired mass mixing.

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arXiv2004

New Constraint on Squark Flavor Mixing from 199Hg EDM

We obtain a new constraint on the CP-violating flavor mixing between the left-handed top scalar quark (\tilde{t}_L) and charm scalar quark (\tilde{c}_L), by considering a chargino loop contribution to chromo-electric dipole moment of strange quark, which is limited by the electric dipole moment of the neutron and atoms. It is found that the flavor mixing should be suppressed to the level of {\cal O}(0.1) for the CP phase of order unity. Although it is much stronger than the known constraint from the chargino loop contribution to b \to s γ, the moderate constraint we obtain here is argued to leave room for sizable supersymmetric contribution to the CP asymmetry in B_d^0 \to ϕK^0.

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arXiv2004

Large Supersymmetric Contribution to CP Asymmetry of B_d \to ϕK_S from Left-Handed Squark Mixing

Supersymmetric contribution to the CP asymmetry of B_d \to ϕK_S is re-examined. It is emphasized that our analysis takes into account the recently found constraint from the mercury electric dipole moment, in addition to the well-known constraint from the branching ratio of b \to s γ. We show that, despite these constraints, the CP asymmetry can considerably deviate from the Standard Model prediction, if the CP-odd flavor mixing comes from left-handed squarks. Alignment mechanism of sfermion masses and mixing may imprint the required flavor mixing at high energy scale.

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