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Fuminobu Takahashi

Publications and source records attributed to Fuminobu Takahashi.

At least 217 records · Page 12Linked to original sources
arXiv2008

Non-Gaussianity from Symmetry

We point out that a light scalar field fluctuating around a symmetry-enhaced point can generate large non-Gaussianity in density fluctuations. We name such a particle as an "ungaussiton", a scalar field dominantly produced by the quantum fluctuations,generating sizable non-Gaussianity in the density fluctuations. We derive a consistency relation between the bispectrum and the trispectrum, tau_NL = 10^3 f_NL^(4/3), which can be extended to arbitrary high order correlation functions. If such a relation is confirmed by future observations, it will strongly support this mechanism.

astro-ph↗
arXiv2008

Gauge Mediation with Sequestered Supersymmetry Breaking

Gauge mediation models have two drawbacks, that is, the so-called μ-problem and a lack of predictability of the gravitino dark matter abundance. We show that conformal sequestering in the supersymmetry breaking sector offers attractive solutions to both problems. The correct mass scale of the μand B_μterms is generated by taking the gravitino mass of O(100) GeV without causing the flavor-changing neutral-current problem. Moreover, a large anomalous dimension of the supersymmetry breaking field naturally realizes the small stau and neutralino mass difference required for the coannihilation to work yielding the right dark matter abundance.

hep-ph↗
arXiv2008

Gravitational Waves as a Probe of the Gravitino Mass

If gaugino condensations occur in the early universe, domain walls are produced as a result of the spontaneous breaking of a discrete R symmetry. Those domain walls eventually annihilate with one another, producing the gravitational waves. We show that the gravitational waves can be a probe for measuring the gravitino mass, if the constant term in the superpotential is the relevant source of the discrete R symmetry breaking.

hep-ph↗
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.

hep-ph↗
arXiv2007

Entropy production by Q-ball decay for diluting long-lived charged particles

The cosmic abundance of a long-lived charged particle such as a stau is tightly constrained by the catalyzed big bang nucleosynthesis. One of the ways to evade the constraints is to dilute those particles by a huge entropy production. We evaluate the dilution factor in a case that non-relativistic matter dominates the energy density of the universe and decays with large entropy production. We find that large Q balls can do the job, which is naturally produced in the gauge-mediated supersymmetry breaking scenario.

hep-ph↗
arXiv2007

Inflaton Decay in Supergravity and Gravitino Problem

We have recently 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 decays into the supersymmetry breaking sector, producing many gravitinos. The inflaton also directly decays into a pair of the gravitinos. Taking account of these processes, we derive constraints on both inflation models and supersymmetry breaking scenarios for avoiding overproduction of the gravitinos.

hep-ph↗
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.

hep-ph↗
arXiv2007

Gravitino Dark Matter from Inflaton Decay

We discuss a scenario that gravitinos produced non-thermally by an inflaton decay constitute dark matter in the present universe. We find that this scenario is realized for wide ranges of the inflaton mass and the vacuum expectation value. What is intriguing about this scenario is that the gravitino dark matter can have a relatively large free streaming length at matter-radiation equality, which can be probed by future observation on QSO-galaxy strong lens system.

hep-ph↗
arXiv2007

Increasing the effective number of neutrinos with decaying particles

We present models of decaying particles for increasing the effective number of neutrinos N_nu after big bang nucleosynthesis but before the structure formation begins. We point out that our scenario not only solves the discrepancy between the constraints on N_nu from these two epochs, but also provides a possible answer to deeper inconsistency in the estimation of the matter power spectrum amplitude at small scales, represented by sigma_8, between the WMAP and some small scale matter power measurements such as the Lyman-alpha forest and weak lensing. We consider (a) saxion decay into two axions; (b) gravitino decay into axino and axion; (c) Dirac right-handed sneutrino decay into gravitino and right-handed neutrino.

hep-ph↗
arXiv2007

Constraint on the Effective Number of Neutrino Species from the WMAP and SDSS LRG Power Spectra

We derive constraint on the effective number of neutrino species N_nu from the cosmic microwave background power spectrum of the WMAP and galaxy clustering power spectrum of the SDSS luminous red galaxies (LRGs). Using these two latest data sets of CMB and galaxy clustering alone, we obtain the limit 0.9 < N_nu < 8.2 (95% C.L.) for the power-law LambdaCDM flat universe, with no external prior. The lower limit corresponds to the lower bound on the reheating temperature of the universe T_R > 2 MeV.

astro-ph↗
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.

hep-ph↗
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.

hep-ph↗
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.

hep-ph↗
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.

hep-ph↗
arXiv2006

The Gravitino-Overproduction Problem in Inflaton Decay

We show that the gravitino-overproduction problem is prevalent among inflation models in supergravity. An inflaton field generically acquires (effective) non-vanishing auxiliary field, if the Kahler potential is non-minimal. The inflaton field then decays into a pair of the gravitinos, thereby severely constraining many of the inflation models especially in the case of the gravity-mediated SUSY breaking.

hep-ph↗
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.

hep-ph↗