Keisuke Harigaya

Composite Models for the 750 GeV Diphoton Excess

Abstract We present composite models explaining the diphoton excess of mass around 750 GeV recently reported by the LHC experiments.

750 GeV Diphotons: Implications for Supersymmetric Unification

A bstractA recent signal of 750 GeV diphotons at the LHC can be explained within the framework of supersymmetric unification by the introduction of vector quarks and leptons with Yukawa couplings to a singlet S that describes the 750 GeV resonance. We study the most general set of theories that allow successful gauge coupling unification, and find that these Yukawa couplings are severely constrained by renormalization group behavior: they are independent of ultraviolet physics and flow to values at the TeV scale that we calculate precisely. As a consequence the vector quarks and leptons must be light; typically in the region of 375 GeV to 700 GeV, and in certain cases up to 1 TeV. The 750 GeV resonance may have a width less than the experimental resolution; alternatively, with the mass splitting between scalar and pseudoscalar components of S arising from one-loop diagrams involving vector fermions, we compute an apparent width of 10s of GeV.

Discovery of Large Scale Tensor Mode and Chaotic Inflation in Supergravity

Abstract 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.

Seesaw Mechanism with Occam's Razor

We discuss the seesaw mechanism which includes the minimum number of parameters for successful leptogenesis and three neutrino oscillations in the spirit of Occam’s razor. We show that models with two right-handed neutrinos with two texture zeros supported by Occam’s razor cannot t the observed neutrino parameters consistently for the normal light neutrino mass hierarchy. For the inverted light neutrino mass hierarchy, on the other hand, we nd that the models can t the observed neutrino parameters consistently. Besides, we show that the model predicts the maximal Dirac CP -phase of the neutrino mixing matrix in the measurable range in the foreseeable future for the inverted neutrino mass hierarchy. We also show that the predicted eective Majorana neutrino mass responsible for the neutrinoless double beta decay is around 50 meV which is also within reach of future experiments.

Dark Matter Production in Late Time Reheating

We estimate dark matter density for the Universe with a reheating temperature smaller than the mass of dark matter, assuming dark matter to be a weakly interacting massive particle. During the reheating process, an inaton decays and releases high energy particles, which are scattered inelastically by the thermal plasma and emit many particles. Dark matters are produced through these inelastic scattering processes and pair creation processes by high energy particles. We properly take account of the Landau-Pomeranchuk-Migdal eect on inelastic processes and show that the resultant energy density of dark matter is much larger than that estimated in the literature and can be consistent with that observed when the mass of dark matter is larger than O(100) GeV.

Chaotic inflation with a fractional power-law potential in strongly coupled gauge theories

Abstract 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.

Thermalization after/during reheating

A bstractIf reheating of the Universe takes place via Planck-suppressed decay, it seems that the thermalization of produced particles might be delayed, since they have large energy/small number densities and number violating large angle scatterings which decrease the momentum of particles by large amount are inefficient correspondingly. In this paper, we study the thermalization of such “under occupied” decay products in detail, following recent developments in understanding the thermalization of non-abelian plasma. Contrary to the above naive expectation, it is shown that in most cases thermalization after/during reheating occurs instantaneously by properly taking account of scatterings with small angles and of particles with small momenta. In particular, the condition for instantaneous thermalization before the completion of reheating is found to be

Simple realization of inflaton potential on a Riemann surface

{\alpha^{{{8 \left/ {5} \right.}}}}\gg \left( {{{{{m_{\phi }}}} \left/ {{{M_{\mathrm{pl}}}}} \right.}} \right){{\left( {{{{M_{\mathrm{pl}}^2{\varGamma_{\phi }}}} \left/ {{m_{\phi}^3}} \right.}} \right)}^{{{1 \left/ {5} \right.}}}}

Dynamical chaotic inflation in the light of BICEP2

, which is much milder than that obtained in previous works with small angle scatterings taken into account.

Peccei-Quinn symmetry from a gauged discrete R symmetry

Abstract 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.