arXiv subjects

Masahiro Ibe

Publications and source records attributed to Masahiro Ibe.

At least 91 records · Page 5Linked to original sources

arXiv2014

Light Higgsinos in Pure Gravity Mediation

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 $μ$-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 $μ\ll m_{3/2}$ 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 $μ$-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.

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arXiv2014

CνB absorption line in the neutrino spectrum at IceCube

The observed neutrino flux can be as a whole well fitted by a simple power-law of the neutrino energy $E_ν$, $E_ν^{-γ_ν}$ ($γ_ν\simeq 2$). As a notable feature of the spectrum, however, it has a gap between 500 TeV and 1 PeV. Although the existence of the gap in the neutrino spectrum is not statistically significant at this point, it is very enticing to ask whether it might hint some physics beyond the Standard Model. In this paper, we investigate a possibility that the gap can be interpreted as an absorption line in the power-law spectrum by the cosmic neutrino background through a new resonance in the MeV range. We also show that the absorption line has rich information about not only the MeV scale new particle but also the neutrino masses as well as the distances to the astrophysical sources of the high energy neutrinos. Viable models to achieve this possibility are also discussed.

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arXiv2014

Coupling Unification and Dark Matter in a Standard Model Extension with Adjoint Majorana Fermions

We revisit an extension of the Standard Model with Majorana fermions in the adjoint representations. There, a precise coupling unification and the good candidate for dark matter (the $SU(2)_L$ triplet fermion) are achieved simultaneously. In particular, we show that the $SU(3)_c$ octet fermion which is required for successful unification can be a good non-thermal source of the triplet fermion dark matter. We also show that the scenario predicts a rather short lifetime of the proton compared with the supersymmetric Standard Model, and the most parameter space can be explored by the future experiments such as the Hyper-Kamiokande experiment.

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arXiv2014

Simple realization of inflaton potential on a Riemann surface

The observation of the B-mode in the cosmic microwave background radiation combined with the so-called Lyth bound suggests the trans-Planckian variation of the inflaton field during inflation. Such a large variation generates concerns over inflation models in terms of the effective field theory below the Planck scale. If the inflaton resides in a Riemann surface and the inflaton potential is a multivalued function of the inflaton field when it is viewed as a function on a complex plane, the Lyth bound can be satisfied while keeping field values in the effective field theory within the Planck scale. We show that a multivalued inflaton potential can be realized starting from a single-valued Lagrangian of the effective field theory below the Planck scale.

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arXiv2014

Wino Dark Matter and Future dSph Observations

We discuss the indirect detection of the wino dark matter utilizing gamma-ray observations of dwarf spheroidal galaxies (dSphs). After carefully reviewing current limits with particular attention to astrophysical uncertainties, we show prospects of the wino mass limit in future gamma-ray observation by the Fermi-LAT and the GAMMA-400 telescopes. We find that the improvement of the so-called $J$-factor of both the classical and the ultra-faint dSphs will play a crucial role to cover whole mass range of the wino dark matter. For example, with $δ(\log_{10}J) = 0.1$ for both the classical and the ultra-faint dSphs, whole wino dark matter mass range can be covered by 15 years and 10 years data at the Fermi-LAT and GAMMA-400 telescopes, respectively.

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arXiv2014

Mass of Decaying Wino from AMS-02 2014

We revisit the decaying wino dark matter scenario in the light of the updated positron fraction, electron and positron fluxes in cosmic ray recently reported by the AMS-02 collaboration. We show the AMS-02 results favor the mass of the wino dark matter at around a few TeV, which is consistent with the prediction on the wino mass in the pure gravity mediation model.

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arXiv2014

Anomaly Mediated Gaugino Mass and Path-Integral Measure

In recent years, there have been controversy concerning the anomaly mediated gaugino mass in the superspace formalism of supergravity. In this paper, we reexamine the gaugino mass term in this formalism by paying particular attention to symmetry which controls gaugino masses in supergravity. We first discuss super-Diffeomorphism invariance of path-integral measures of charged superfields. As we will show, the super-Diffeomorphism invariant measure is not invariant under a super-Weyl transformation, which is the origin of the anomaly mediated gaugino mass. We show how the anomaly mediated gaugino mass is expressed as a local operator in a Wilsonian effective action in a super-Diffeomorphism covariant way. We also obtain a gaugino mass term independent of the gauge choice of the fictitious super-Weyl symmetry in the super-Weyl compensator formalism, which reproduces the widely accepted result. Besides, we discuss how to reconcile the gaugino mass term in the local Wilsonian effective action and the gaugino mass term appearing in a non-local 1PI quantum effective action.

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arXiv2014

R-symmetric Axion/Natural Inflation in Supergravity via Deformed Moduli Dynamics

We construct a natural inflation model in supergravity where the inflaton is identified with a modulus field possessing a shift symmetry. The superpotential for the inflaton is generated by meson condensation due to strong dynamics with deformed moduli constraints. In contrast to models based on gaugino condensation, the inflaton potential is generated without $R$-symmetry breaking and hence does not depend on the gravitino mass. Thus, our model is compatible with low scale supersymmetry.

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arXiv2014

Phase Locked Inflation -- Effectively Trans-Planckian Natural Inflation

A model of natural inflation with an effectively trans-Planckian decay constant can be easily achieved by the "phase locking" mechanism while keeping field values in the effective field theory within the Planck scale. We give detailed description of "phase locked" inflation based on this mechanism. We also construct supersymmetric natural inflation based on this mechanism and show that the model is consistent with low scale supersymmetry. We also investigate couplings of the inflaton with the minimal supersymmetric standard model to achieve an appropriate reheating process. Interestingly, in a certain class of models, we find that the inflation scale is related to the mass of the right-handed neutrino in a consistent way with the seesaw mechanism.

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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.

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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.

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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.

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arXiv2014

High-Scale SUSY Breaking Models in light of the BICEP2 Result

The large value of the tensor-to-scalar ratio in the cosmic microwave background radiation reported by the BICEP2 collaboration gives strong impact on models of supersymmetry (SUSY). The large ratio indicates inflation with a high-energy scale and thus a high reheating temperature in general, and various SUSY models suffer from the serious gravitino and Polonyi problems. In this article, we discuss a class of the high-scale SUSY breaking models which are completely free from those problems. With especially focusing on the dark matter relic abundance, we examine how the BICEP2 result narrows down the parameter space of the models, assuming the simplest chaotic inflation model. We find that the mass of the dark matter is predicted to be less than about 1 TeV thanks to the non-thermal production in the early universe through the decay of abundant gravitinos produced after the reheating process. We also discuss implications in some details to dark matter searches at collider and indirect dark matter detection experiments.

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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.

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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.

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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.

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arXiv2013

One-Loop Anomaly Mediated Scalar Masses and (g-2)_mu in Pure Gravity Mediation

We consider the effects of non-universalities among sfermion generations in models of Pure Gravity Mediation (PGM). In PGM models and in many models with strongly stabilized moduli, the gravitino mass may be O(100) TeV, whereas gaugino masses, generated through anomalies at 1-loop, remain relatively light O(1) TeV. In models with scalar mass universality, input scalar masses are generally very heavy (m_0 \simeq m_{3/2}) resulting in a mass spectrum resembling that in split supersymmetry. However, if one adopts a no-scale or partial no-scale structure for the Kähler manifold, sfermion masses may vanish at the tree level. It is usually assumed that the leading order anomaly mediated contribution to scalar masses appears at 2-loops. However, there are at least two possible sources for 1-loop scalar masses. These may arise if Pauli-Villars fields are introduced as messengers of supersymmetry breaking. We consider the consequences of a spectrum in which the scalar masses associated with the third generation are heavy (order m_{3/2}) with 1-loop scalar masses for the first two generations. A similar spectrum is expected to arise in GUT models based on E_7/SO(10) where the first two generations of scalars act as pseudo-Nambu-Goldstone bosons. Explicit breaking of this symmetry by the gauge couplings then generates one-loop masses for the first two generations. In particular, we show that it may be possible to reconcile the g_mu - 2 discrepancy with potentially observable scalars and gauginos at the LHC.

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arXiv2013

A Closer Look at Gaugino Masses in Pure Gravity Mediation Model/Minimal Split SUSY Model

We take a closer look at the gaugino masses in the context of pure gravity mediation models/minimal split SUSY models. We see that the gaugino mass spectrum has a richer structure in the presence of vector-like matter fields even when they couple to the supersymmetry breaking sector only through Planck suppressed operators. For example, the gluino mass can be much lighter than in anomaly mediation, enhancing the detectability of the gluino at the LHC experiments. The rich gaugino spectrum also allows new possibilities for dark matter scenarios such as the bino-wino co-annihilation, bino-gluino co-annihilation, or even wino-gluino co-annihilation scenarios, which affects future collider experiments as well as dark matter search experiments.

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