arXiv subjects

Tsutomu T. Yanagida

Publications and source records attributed to Tsutomu T. Yanagida.

At least 199 records · Page 11Linked to original sources

arXiv2014

Dynamical Fractional Chaotic Inflation -- Dynamical Generation of a Fractional Power-Law Potential for Chaotic Inflation

Chaotic inflation based on a simple monomial scalar potential, V(phi) ~ phi^p, is an attractive large-field model of inflation capable of generating a sizable tensor-to-scalar ratio r. Therefore, assuming that future CMB 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 (DCI), 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 towards a more complete theory of dynamical chaotic inflation.

hep-ph↗

arXiv2014

Pure Gravity Mediation and Chaotic Inflation in Supergravity

We investigate compatibility of the pure gravity mediation (or the minimal split supersymmetry) with chaotic inflation models in supergravity. We find that an approximate Z2 parity of the inflaton is useful to suppress gravitino production from thermal bath and to obtain consistent inflation dynamics. We discuss production of the lightest supersymmetric particle through the decay of the inflaton with the approximate Z2 symmetry and find that a large gravitino mass is favored to avoid the overproduction of the lightest supersymmetric particle, while a lower gravitino mass requires tuning of parameters. This may explain why the nature has chosen the gravitino mass of O(100) TeV rather than O(100) GeV.

hep-ph↗

arXiv2014

Kinetic Term Anarchy for Polynomial Chaotic Inflation

We argue that there may arise a relatively flat inflaton potential over super-Planckian field values with an approximate shift symmetry, if the coefficients of the kinetic terms for many singlet scalars are subject to a certain random distribution. The inflaton potential generically contains various shift-symmetry breaking terms, leading to a possibly large deviation of the predicted values of the spectral index and tensor-to-scalar ratio from those of the simple quadratic chaotic inflation. We revisit a polynomial chaotic inflation in supergravity as such.

hep-ph↗

arXiv2014

Universality in Pure Gravity Mediation

If low energy supersymmetry is realized in nature, the apparent discovery of a Higgs boson with mass around 125 GeV points to a supersymmetric mass spectrum in the TeV or multi-TeV range. Multi-TeV scalar masses are a necessary component of supersymmetric models with pure gravity mediation or in any model with strong moduli stabilization. Here, we show that full scalar mass universality remains viable as long as the ratio of Higgs vevs, tan beta is relatively small (\lesssim 2.5). We discuss in detail the low energy (observable) consequences of these models.

hep-ph↗

arXiv2014

Discovery of Large Scale Tensor Mode and Chaotic Inflation in Supergravity

The BICEP2 collaboration has recently reported a large tensor fluctuation in the cosmic microwave background, which suggests chaotic inflation models. In this letter, we reconsider the chaotic inflation model in the supergravity. We introduce a non-holomorphic shift-symmetry breaking parameter, which we expect to exist in general, and discuss its effect on the inflaton dynamics. We show that the model predicts a sizable deviation from the original chaotic inflation model and the predicted tensor fluctuation can lie between the BICEP2 result and the upper bound given by the Planck experiment with a small shift-symmetry breaking parameter. The model is characterized by only two parameters, which yields predictability and testability in future experiments.

hep-ph↗

arXiv2014

Extra light fermions in $E_6$-inspired models and the 3.5 keV X-ray line signal

We propose a scenario in which extra light fermions in an $E_6$-inspired U(1) extension of the standard model constitute the dark matter, as a simple variation of our model for dark radiation presented in 2010. Interestingly, for the light fermions of mass about 7 keV, they radiatively decay into active neutrinos and photons with a lifetime in the range of $10^{27}-10^{28}$ seconds, which naturally explains the recently discovered 3.5 keV X-ray line signal.

hep-ph↗

arXiv2014

Multi-hadron final states in RPV supersymmetric models with extra matters

The gluino mass has been constrained by various search channels at the LHC experiments and the recent analyses are even sensitive to the cases where gluinos decay to quarks at the end of the decay chains through the baryonic RPV operator. We argue that introduction of extra matters, which is partly motivated by cancelling anomalies of discrete R symmetry, may help to relax the gluino mass limit when the RPV hadronic gluino decays are considered. In the scenarios where the extra matter states appear in the gluino decay chains, the number of decay products increases and each jet becomes soft, making it difficult to distinguish the signal from backgrounds. We investigate the sensitivity of existing analyses to such scenarios and demonstrate that the gluino mass limit can be relaxed if the mass spectrum reconciles the sensitivities of high $p_T$ jet searches and large jet multiplicity searches.

hep-ph↗

arXiv2014

Sneutrino Chaotic Inflation and Landscape

The most naive interpretation of the BICEP2 data is the chaotic inflation by an inflaton with a quadratic potential. When combined with supersymmetry, we argue that the inflaton plays the role of right-handed scalar neutrino based on rather general considerations. The framework suggests that the right-handed sneutrino tunneled from a false vacuum in a landscape to our vacuum with a small negative curvature and suppressed scalar perturbations at large scales.

hep-ph↗

arXiv2014

Gravitino Problem in Supergravity Chaotic Inflation and SUSY Breaking Scale after BICEP2

Gravitinos are generically produced by inflaton decays, which place tight constraints on inflation models as well as supersymmetry breaking scale. We revisit the gravitino production from decays of the inflaton and the supersymmetry breaking field, based on a chaotic inflation model suggested by the recent BICEP2 result. We study cosmological constraints on thermally and non-thermally produced gravitinos for a wide range of the gravitino mass, and show that there are only three allowed regions of the gravitino mass: $m_{3/2}\lesssim 16$eV, $m_{3/2}\simeq 10$--$1000$TeV and $m_{3/2}\gtrsim 10^{13}$GeV.

hep-ph↗

arXiv2014

Upper Bounds on Gluino, Squark and Higgisino Masses in the Focus Point Gaugino Mediation with a Mild Fine Tuning $Δ\le 100$

We show that upper bounds on the masses for gluino, squarks and higgsino are $m_{gluino} \le 5.5$ TeV, $m_{squark} \le 4.7$ TeV and $m_{higgsino} \le 650$ GeV in a focus point gaugino mediation. Here, we impose a mild fine tuning $Δ\le 100$. This result shows that it is very challenging for the LHC to exclude the focus point gaugino mediation with the mild fine tuning. However, the ILC may have a potential for excluding the focus point gaugino mediation with such a mild fine tuning. It is also shown that vector-like matters reduce the required masses of the squark (stop) and gluino to explain the observed Higgs boson mass and enhance the testability of the model at the LHC. The fine-tuning is still kept mild.

hep-ph↗

arXiv2014

Anomaly-free flavor models for Nambu-Goldstone bosons and the 3.5 keV X-ray line signal

We pursue a possibility that a pseudo-Nambu-Goldstone boson is lurking around or below the intermediate scale. To this end we consider an anomaly-free global flavor symmetry, and construct models where the pseudo-Nambu-Goldstone boson is coupled preferentially to leptons. The experimental and astrophysical bounds derived from couplings to photons and nucleons are significantly relaxed. If sufficiently light, the pseudo-Nambu-Goldstone boson contributes to dark matter, and interestingly, it generally decays into photons through couplings arising from threshold corrections. We show that the recent hint for the X-ray line at about $3.5$ keV can be explained by the decay of such pseudo-Nambu-Goldstone boson of mass about $7$ keV with the decay constant of order $10^{10}$ GeV, if the electron is charged under the flavor symmetry.

hep-ph↗

arXiv2014

Dynamical Chaotic Inflation in the Light of BICEP2

The measurement of a large tensor-to-scalar ratio by the BICEP2 experiment, r = 0.20 (-0.05)(+0.07), severely restricts the landscape of viable inflationary models and shifts attention once more towards models featuring large inflaton field values. In this context, chaotic inflation based on a fractional power-law potential that is dynamically generated by the dynamics of a strongly coupled supersymmetric gauge theory appears to be particularly attractive. We revisit this class of inflation models and find that, in the light of the BICEP2 measurement, models with a non-minimal gauge group behind the dynamical model seem to be disfavored, while the model with the simplest group, i.e. SU(2), is consistent with all results. We also discuss how the dynamical model can be distinguished from the standard chaotic inflation model based on a quadratic inflaton potential.

hep-ph↗

arXiv2014

The 3.5 keV X-ray line signal from decaying moduli with low cutoff scale

The recent unidentified 3.5 keV X-ray line signal can be explained by decaying moduli dark matter with a cutoff scale one order of magnitude smaller than the Planck scale. We show that such modulus field with the low cutoff scale follows a time-dependent potential minimum and its abundance is reduced by the adiabatic suppression mechanism. As a result the modulus abundance can naturally be consistent with the observed dark matter abundance without any fine-tuning of the initial oscillation amplitude.

hep-ph↗

arXiv2014

Testing the Minimal Direct Gauge Mediation at the LHC

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.

hep-ph↗

arXiv2014

Charge Quantization and the Standard Model from the $\mathbb{CP}^2$ and $\mathbb{CP}^3$ Nonlinear $σ$-Models

We investigate charge quantization in the Standard Model (SM) through a $\mathbb{CP}^2$ nonlinear sigma model (NLSM), $SU(3)_G/(SU(2)_H \times U(1)_H)$, and a $\mathbb{CP}^3$ model, $SU(4)_G/(SU(3)_H \times U(1)_H)$. We also generalize to any $\mathbb{CP}^k$ model. Charge quantization follows from the consistency and dynamics of the NLSM, without a monopole or Grand Unified Theory, as shown in our earlier work on the $\mathbb{CP}^1$ model (arXiv:1309.0692). We find that representations of the matter fields under the unbroken non-abelian subgroup dictate their charge quantization under the $U(1)_H$ factor. In the $\mathbb{CP}^2$ model the unbroken group is identified with the weak and hypercharge groups of the SM, and the Nambu-Goldstone boson (NGB) has the quantum numbers of a SM Higgs. There is the intriguing possibility of a connection with the vanishing of the Higgs self-coupling at the Planck scale. Interestingly, with some minor assumptions (no vector-like matter and minimal representations) and starting with a single quark doublet, anomaly cancellation requires the matter structure of a generation in the SM. Similar analysis holds in the $\mathbb{CP}^3$ model, with the unbroken group identified with QCD and hypercharge, and the NGB having the up quark as a partner in a supersymmetric model. This can motivate solving the strong CP problem with a vanishing up quark mass.

hep-th↗

arXiv2014

Peccei-Quinn Symmetric Pure Gravity Mediation

Successful models of Pure Gravity Mediation (PGM) with radiative electroweak symmetry breaking can be expressed with as few as two free parameters which can be taken as the gravitino mass and $\tan β$. These models easily support a 125-126 GeV Higgs mass at the expense of a scalar spectrum in the multi-TeV range and a much lighter wino as the lightest supersymmetric particle. In these models, it is also quite generic that the Higgs mixing mass parameter, $μ$, which is determined by the minimization of the Higgs potential is also in the multi-TeV range. For $μ> 0$, the thermal relic density of winos is too small to account for the dark matter. The same is true for $μ< 0$ unless the gravitino mass is of order 500 TeV. Here, we consider the origin of a multi-TeV $μ$ parameter arising from the breakdown of a Peccei-Quinn (PQ) symmetry. A coupling of the PQ-symmetry breaking field, $P$, to the MSSM Higgs doublets, naturally leads to a value of $μ\sim \langle P \rangle^2 /M_P \sim \mathcal{O}(100)$ TeV and of order that is required in PGM models. In this case, axions make up the dark matter or some fraction of the dark matter with the remainder made up from thermal or non-thermal winos. We also provide solutions to the problem of isocurvature fluctuations with axion dark matter in this context.

hep-ph↗

arXiv2014

Chaotic Inflation with Right-handed Sneutrinos after Planck

We propose a chaotic inflation model in which the lightest right-handed sneutrino serves as the inflaton and the predicted values of the spectral index and tensor-to-scalar ratio are consistent with the Planck data. Interestingly, the observed magnitude of primordial density perturbations is naturally explained by the inflaton mass of order $10^{13}$GeV, which is close to the right-handed neutrino mass scale suggested by the seesaw mechanism and the neutrino oscillation experiments. We find that the agreement of the two scales becomes even better in the neutrino mass anarchy. We show that the inflation model can be embedded into supergravity and discuss thermal history of the Universe after inflation such as non-thermal leptogenesis by the right-handed sneutrino decays and the modulus dynamics.

hep-ph↗

arXiv2014

Flat Higgs Potential from Planck Scale Supersymmetry Breaking

The observed Higgs boson mass poses a new puzzle in addition to the longstanding problem of the origin of the electroweak scale; the shallowness of the Higgs potential. The Higgs quartic coupling even seems to vanish at around the Planck scale within the uncertainties of the top quark mass and the strong gauge coupling. We show that the shallowness of the Higgs potential might be an outcome of supersymmetry breaking at around the Planck scale. There, the electroweak fine-tuning in the Higgs quadratic terms leads to an almost vanishing quartic coupling at around the Planck scale.

hep-ph↗