arXiv subjects

Yuya Yamaguchi

Publications and source records attributed to Yuya Yamaguchi.

23 records · Page 2Linked to original sources

arXiv2014

Axion monodromy inflation with multi-natural modulations

We study parameter space in the axion monodromy inflation corrected by dynamically generated terms involving with the axion. The potential has the linear potential with multiple sinusoidal functions, which play a role in generating modulations. We show that this potential leads both to a large tensor-to-scalar ratio $r_T \sim 0.16$ and to a large negative running of spectral index $α_s \sim - (0.02 -0.03)$. To realize these results, a small hierarchy among dynamical scales is required whereas the decay constants in sinusoidal functions remain sub-Planckian in this model. We discuss also reheating process after the inflation in a bottom-up approach.

hep-ph↗

arXiv2014

Axion monodromy inflation with sinusoidal corrections

We study the axion monodromy inflation with a non-perturbatively generated sinusoidal term. The potential form is a mixture between the natural inflation and the axion monodromy inflation potentials. The sinusoidal term is subdominant in the potential, but leaves significant effects on the resultant fluctuation generated during inflation. A larger tensor-to-scalar ratio can be obtained in our model. We study two scenarios, single inflation scenario and the double inflation scenario. In the first scenario, the axion monodromy inflation with a sufficient number of e-fold generates a larger tensor-to-scalar ratio about $0.1 - 0.15$ but also a tiny running of spectral index. In the second scenario of double inflation, axion monodromy inflation is its first stage and, we assume another inflation follows. In this case, our model can realize a larger tensor-to-scalar ratio and a large negative running of spectral index simultaneously.

hep-ph↗

arXiv2014

Accurate renormalization group analyses in neutrino sector

We investigate accurate renormalization group analyses in neutrino sector between $ν$-oscillation and seesaw energy scales. We consider decoupling effects of top quark and Higgs boson on the renormalization group equations of light neutrino mass matrix. Since the decoupling effects are given in the standard model scale and independent of high energy physics, our method can basically apply to any models beyond the standard model. We find that the decoupling effects of Higgs boson are negligible, while those of top quark are not. Particularly, the decoupling effects of top quark affect neutrino mass eigenvalues, which are important for analyzing predictions such as mass squared differences and neutrinoless double beta decay in an underlying theory existing at high energy scale.

hep-ph↗

arXiv2014

Neutrino mass from neutrinophilic Higgs and leptogenesis

In a class of two Higgs doublet model, where one Higgs doublet generates masses of quarks and charged leptons whereas the other Higgs doublet with a tiny vacuum expectation value (VEV) generates neutrino Dirac masses, smallness of neutrino masses might be understand as the consequence of the small second Higgs VEV. In this framework, thermal leptogenesis scenarios work well at low energy scale and have several advantages as follows. Under the assumption of hierarchical right-handed neutrino masses, the lightest right-handed neutrino can be as light as ${\cal O}(10^2)$ TeV.The required degeneracy for successful resonant leptogenesis also can be significantly reduced as small as ${\cal O}(10^4)$. Availability of low scale thermal leptogenesis provides a novel solution to gravitino problem in supergravity models.

hep-ph↗

arXiv2013

Resonant leptogenesis with mild degeneracy

Under the assumption of hierarchical right-handed neutrino masses, masses of right-handed neutrinos must be larger than $10^8$ GeV in the standard thermal leptogenesis scenario, while the mass can be reduced to around 5 TeV in a neutrinophilic two Higgs doublet model. On the other hand, resonant leptogenesis can work with the masses of TeV-scale. However, necessary degeneracy between the lightest and the second lightest right-handed neutrino masses means unnatural fine-tuning of the order of $10^9$. In this paper, we will investigate the resonant leptogenesis scenario in a neutrinophilic two Higgs doublet model. We will find the mass can be reduced to 2 TeV and the degeneracy becomes much milder as of the order of $10^4$. We will also show that degenerate mass spectrum of active neutrinos is disfavored in this setup.

hep-ph↗