arXiv subjects

Masahiro Ibe

Publications and source records attributed to Masahiro Ibe.

At least 109 records · Page 6Linked to original sources

arXiv2013

Mixed (Cold+Warm) Dark Matter in the Bino-Wino co-annihilation scenario

We study phenomenological aspects of the bino-wino co-annihilation scenario in high-scale supersymmetry breaking models. High-scale SUSY breaking scenarios are considered to be promising possibility after the discovery of the Higgs boson with a mass around 126 GeV. In this paper, we discuss the bino lightest supersymmetric particle (LSP) accompanied by the at most around 30 GeV heavier wino. With the suitable mass splitting between the bino and the wino, the bino LSP has the correct relic abundance of dark matter. For the smaller mass splitting, the late-time decay of the gravitino can provide the correct abundance of the bino dark matter. It is extremely challenging to find signals from the bino dark matter in direct and indirect detections. By utilizing multi-jets plus missing transverse momentum events at the LHC, we can constraint the gluino mass and thus probe the bino-wino co-annihilation scenario indirectly. The collider experiment, however, can not search the bino dark matter directly. In this paper, we suggest the direct probe of the bino dark matter. We show that the bino dark matter leaves imprints on the small-scale matter power spectrum when the bino dark matter is produced by the decay of the gravitino. The non-thermal bino dark matter behaves as mixed (cold+warm) dark matter.

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arXiv2013

Lower Bound on the Garvitino Mass $m_{3/2}>O(100)$ TeV in $R$-Symmetry Breaking New Inflation

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, $m_{3/2}>O(100)$ TeV. This lower limit is consistent with the observed Higgs mass of 126 GeV when the masses of the stops are of order the gravitino mass scale.

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arXiv2013

Hypercharged Dark Matter and Direct Detection as a Probe of Reheating

The lack of new physics at the LHC so far weakens the argument for TeV scale thermal dark matter. On the other hand, heavier, non-thermal dark matter is generally difficult to test experimentally. Here we consider the interesting and generic case of hypercharged dark matter, which can allow for heavy dark matter masses without spoiling testability. Planned direct detection experiments will be able to see a signal for masses up to an incredible $10^{10}$ GeV, and this can further serve to probe the reheating temperature up to about $10^9$ GeV, as determined by the non-thermal dark matter relic abundance. The $Z$-mediated nature of the dark matter scattering may be determined in principle by comparing scattering rates on different detector nuclei, which in turn can reveal the dark matter mass. We will discuss the extent to which future experiments may be able to make such a determination.

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arXiv2013

The Peccei-Quinn Symmetry from a Gauged Discrete R Symmetry

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 symmetry, U(1)_PQ, to such a high degree of accuracy. In this paper, we point out that the U(1)_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 mu problem, collider searches for vector-like quarks and axion dark matter.

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arXiv2013

AMS-02 Positrons from Decaying Wino in the Pure Gravity Mediation Model

The AMS-02 collaboration has recently reported an excess of the cosmic-ray positron fraction, which turned out to be consistent with previous results reported by the PAMELA and Fermi-LAT collaborations. A decaying dark matter with the mass around 1 TeV can be responsible for the excess of the positron fraction when it is interpreted as a dark matter signal. Interestingly, the pure gravity mediation model provides such a dark matter, namely an almost pure neutral wino dark matter, when a tiny R-parity violation through $LLE^c$ interactions is introduced. We show that the decaying wino dark matter well reproduces the energy spectrum of the fraction with being consistent with constraints from cosmic-ray anti-proton and gamma-ray observations.

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arXiv2013

Focus point gauge mediation in product group unification

In certain models of gauge-mediated supersymmetry breaking with messenger fields in incomplete GUT multiplets, the radiative corrections to the Higgs potential cancel out during renormalization group running. This allows for relatively heavy superpartners and for a 125 GeV Higgs while the fine-tuning remains modest. In this paper, we show that such gauge mediation models with "focus point" behaviour can be naturally embedded into a model of SU(5) x U(3) product group unification.

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arXiv2013

Non-Universalities in Pure Gravity Mediation

The simplest model of pure gravity mediation contains only two free parameters: the gravitino mass and \tanβ. Scalar masses are universal at some high energy renormalization scale and gaugino masses are determined through anomalies and depend on the gravitino mass and the gauge couplings. This theory requires a relatively large gravitino mass (m_{3/2}\gtrsim 300\,TeV) and a limited range in \tan β\simeq 1.7--2.5. Here we generalize the theory to allow for non-universality in the Higgs soft masses. This introduces zero, one or two new free parameters associated with Higgs soft masses. This generalization allows us to greatly increase the allowed range in \tan βand it allows one to find viable solutions with lower m_{3/2}. The latter is important if we hope to find a low energy signal from gluinos. Some special cases of these non-universalities are suggestive of Higgs bosons as Nambu-Goldstone bosons or a partial no-scale structure for the Higgs doublets. Thus, we probe signatures at the weak scale and structures at the GUT and/or Planck scale.

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arXiv2013

Recent Result of the AMS-02 Experiment and Decaying Gravitino Dark Matter in Gauge Mediation

The AMS-02 collaboration has recently reported an excess of cosmic-ray positron fractions, which is consistent with previous results at PAMELA and Fermi-LAT experiments. The result indicates the existence of new physics phenomena to provide the origin of the energetic cosmic-ray positron. We pursue the possibility that the enhancement of the positron fraction is due to the decay of gravitino dark matter. We discuss that such a scenario viably fits into the models in which the soft SUSY breaking parameters are dominantly from gauge-mediation mechanism with superparticle masses of around 10 TeV. Our scenario is compatible with ~126 GeV Higgs boson, negative searches for SUSY particles, and non-observation of anomalous FCNC processes. We also point out that the scenario will be tested in near future by measuring the electric dipole moment of the electron and the lepton flavor violating decay of the muon.

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arXiv2013

Muon g-2 and 125 GeV Higgs in Split-Family Supersymmetry

We discuss the minimal supersymmetric standard model with "split-family" spectrum where the sfermions in the first two generations are in the hundreds GeV to a TeV range while the sfermions in the third generation are in the range of tens TeV. With the split-family spectrum, the deviation of the muon g-2 and the observed Higgs boson mass are explained simultaneously. It is predicted that the gluino and the squarks in the first two generations are within the reach of the LHC experiments in most favored parameter space for the universal gaugino mass, which can be tested by searching for events with missing transverse energy or events with stable charged massive particles. We also point out that the split-family scenario can be consistent with the focus point scenario for the non-universal gaugino masses where the required mu-term is in the hundreds GeV range.

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arXiv2013

Mass Splitting between Charged and Neutral Winos at Two-Loop Level

The recent result of the higgs search at the LHC experiment has lead to more attention to the supersymmetric standard models with heavy sfermions. Among them, the models with the almost pure wino being the lightest supersymmetric particle (LSP) have been widely discussed due to their success in providing a consistent dark matter candidate. The notable phenomenological feature of the wino LSP is the degeneracy with its charged SU(2)_L partner (the charged wino) in mass. The tiny mass splitting makes the charged wino long-lived, which allows us to detect the wino production at the LHC experiment by searching for the disappearing charged tracks inside the detectors. Since the reach of the experiment is sensitive to the mass splitting, it is mandatory to estimate it very precisely. We therefore perform a full calculation of the mass splitting at two-loop level, and find that the splitting is reduced by a few MeV compared to the one-loop calculation. This reduction leads to about a 30 % longer lifetime of the charged wino, with which the current constraint on the wino mass by the ATLAS experiment is improved by about 10 %.

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arXiv2013

Heavy Squarks and Light Sleptons in Gauge Mediation ~From the viewpoint of 125 GeV Higgs Boson and Muon g-2~

In the framework of gauge mediation models, we investigate scenarios with heavy squarks and light sleptons, motivated by the recent discovery of the Higgs boson and the deviation of the muon anomalous magnetic moment (g-2) from the SM prediction. We show that only models with a messenger multiplet in the adjoint representation of SU(5) GUT gauge group are the unique possibility that sleptons are light enough to explain the muon g-2 in the minimal setup. We also show that, if there is an additional source of the Higgs soft masses, the muon g-2 can be explained with messenger multiples in the fundamental representation of SU(5) with the help of the light higgsino. Some phenomenological aspects of these models are also discussed.

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arXiv2013

A Simple Solution to the Polonyi Problem in Gravity Mediation

The Polonyi field is a necessary ingredient in any viable scenario of gravity mediated supersymmetry breaking. However, it is known that the presence of the Polonyi field leads to several serious cosmological problems, which are collectively referred to as the Polonyi problem. We show that the Polonyi problem can be solved if the Polonyi field couples to a pseudo modulus in the superpotential and this pseudo modulus has a large field expectation value during inflation. To illustrate our idea, we construct an explicit model which can be readily connected to scenarios of gravity mediation. The generation of the mass parameters contained in our model by strong gauge dynamics is also commented on.

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arXiv2013

Natural SUSY's Last Hope: R-parity Violation via UDD Operators

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) X U(3). In this model, mixing of the SM quarks with additional quark like 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 non-universal, a natural consequence of product unification.

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arXiv2012

Chaotic Inflation with a Fractional Power-Law Potential in Strongly Coupled Gauge Theories

Models of chaotic inflation with a fractional power-law potential are not only viable but also testable in the foreseeable future. We show that such models can be realized in simple strongly coupled supersymmetric gauge theories. In these models, the energy scale during inflation is dynamically generated by the dimensional transmutation due to the strong gauge dynamics. Therefore, such models not only explain the origin of the fractional power in the inflationary potential but also provide a reason why the energy scale of inflation is much smaller than the Planck scale.

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arXiv2012

Non-Gaussianity from Attractor Curvaton

We propose a curvaton model in which the initial condition of the curvaton oscillation is determined by its attractor behavior during inflation. Assuming a chaotic inflation model, we find that the initial condition determined by the attractor behavior is appropriate to generate a sizable non-Gaussianity contribution to the curvature perturbation, which will be tested in the foreseeable future. Implications on the thermal history of the universe and on particle physics models are also discussed.

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arXiv2012

Non-Anomalous Discrete R-symmetry Decrees Three Generations

We show that more than two generations of quarks and leptons are required to have an anomaly free discrete R-symmetry larger than R-parity, provided that the supersymmetric Standard Model can be minimally embedded into a grand unified theory. This connects an explanation for the number of generations with seemingly unrelated problems like supersymmetry breaking, proton decay, the mu problem, and the cosmological constant through a discrete R-symmetry. We also show that three generations is uniquely required by a non-anomalous discrete R-symmetry in classes of grand unified theories such as the ones based on (semi-)simple gauge groups.

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arXiv2012

Imprints of Non-thermal Wino Dark Matter on Small-Scale Structure

We study how "warm" the wino dark matter is when it is non-thermally produced by the decays of the gravitino in the early Universe. We clarify the energy distribution of the wino at the decay of the gravitino and the energy loss process after their production. By solving the Boltzmann equation, we show that a sizable fraction of the wino dark matter can be "warm" for the wino mass m_{\tilde w} \sim 100-500 GeV. The "warmness" of the wino dark matter leaves imprints on the matter power spectra and may provide further insights on the origin of dark matter via the future 21 cm line survey. Our calculations can be applied to other non-thermal wino production scenarios such as the wino dark matter produced by the decay of the moduli fields.

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arXiv2012

A 125 GeV Higgs Boson Mass and Gravitino Dark Matter in R-invariant Direct Gauge Mediation

We discuss the SM-like Higgs boson mass in the MSSM in an R-invariant direct gauge mediation model with the gravitino mass in the O(1) keV range. The gravitino dark matter scenario in this mass range is a good candidate for a slightly warm dark matter. We show that the Higgs boson mass around 125 GeV suggested by the ATLAS and CMS experiments can be easily achieved in the direct gauge mediation model with this gravitino mass range.

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