arXiv subjects

T. Fujihara

Publications and source records attributed to T. Fujihara.

6 recordsLinked to original sources

arXiv2009

High density quark matter in the NJL model with dimensional vs. cut-off regularization

We investigate color superconducting phase at high density in the extended Nambu--Jona-Lasinio model for the two flavor quarks. Because of the non-renormalizability of the model, physical observables may depend on the regularization procedure, that is why we apply two types of regularization, the cut-off and the dimensional one to evaluate the phase structure, the equation of state and the relationship between the mass and the radius of a dense star. To obtain the phase structure we evaluate the minimum of the effective potential at finite temperature and chemical potential. The stress tensor is calculated to derive the equation of state. Solving the Tolman-Oppenheimer-Volkoff equation, we show the relationship between the mass and the radius of a dense star. The dependence on the regularization is found not to be small for these phenomena in the color superconducting phase.

hep-ph↗

arXiv2008

Reconsideration of the 2-flavor NJL model with dimensional regularization at finite temperature and density

We study the 2-flavor Nambu--Jona-Lasinio (NJL) model at finite temperature, $T$, and chemical potential, $μ$, in the dimensional regularization. The pion and sigma meson masses are calculated at finite $T$ and $μ$. The color superconductivity is also discussed in the extended NJL model. We obtain the phase structure of the chiral and color symmetry in the dimensional regularization and compare the results with ones obtained in the cut-off regularization.

hep-ph↗

arXiv2007

Influence of QED Corrections on the Orientation of Chiral Symmetry Breaking in the NJL model

We study QED corrections to chiral symmetry breaking in the Nambu--Jona-Lasinio (NJL) model with two flavors of quarks. In this model, the isospin symmetry is broken by the differences between the current quark masses and the electromagnetic charges of the up and down quarks. To leading order in the 1/N expansion, we calculate the effective potential of the model with one-loop QED corrections at finite temperature. Evaluating the effective potential, we study the influence of the isospin symmetry breaking on the orientation of chiral symmetry breaking. The current quark mass plays an essential role in maintaining the orientation of the chiral symmetry breaking. If the average of the up and down quark masses is small enough, we find a phase in which the pion field has non-vanishing expectation value and dynamical CP violation takes place.

hep-ph↗

arXiv2005

Color Superconductivity and Radius of Quark Star in Extended NJL Model by Using the Dimensional Regularization

A radius of a dense star on the color superconducting phase is investigated in an extended NJL type model with two flavors of quarks. Since the model is non-renormalizable, the results depend on the regularization procedure. Here we apply the dimensional regularization and evaluate the radius of a dense star. Evaluating the TOV equation, we show the relationship between mass and radius of the dense star in the dimensional regularization.

hep-ph↗

arXiv2005

Low scale Seesaw model and Lepton Flavor Violating Rare B Decays

We study lepton flavor number violating rare B decays, $b \to s l_h^{\pm} l_l^{\mp}$, in a seesaw model with low scale singlet Majorana neutrinos motivated by the resonant leptogenesis scenario. The branching ratios of inclusive decays $ b \to s l_h^{\pm} \bar{l_l}^{\mp} $ with two almost degenerate singlet neutrinos at TeV scale are investigated in detail. We find that there exists a class of seesaw model in which the branching fractions of $ b \to s τμ$ and $τ\to μγ$ can be as large as $10^{-10}$ and $10^{-9}$ within the reach of Super B factories, respectively, without being in conflict with neutrino mixings and mass squared difference of neutrinos from neutrino data, invisible decay width of $Z$ and the present limit of $Br(μ\to e γ)$.

hep-ph↗

arXiv2005

Cosmological Family Asymmetry and CP violation

We discuss how the cosmological baryon asymmetry can be achieved by the lepton family asymmetries of heavy Majorana neutrino decays and they are related to CP violation in neutrino oscillation, in the minimal seesaw model with two heavy Majorana neutrinos. We derive the most general formula for CP violation in neutrino oscillation in terms of the heavy Majorana masses and Yukawa mass term. It is shown that the formula is very useful to classify several models in which $e-$, $μ-$ and $τ-$leptogenesis can be separately realized and to see how they are connected with low energy CP violaton. To make the models predictive, we take texture with two zeros in the Dirac neutrino Yukawa matrix. In particular, we find some interesting cases in which CP violation in neutrino oscillation can happen while lepton family asymmetries do not exist at all. On the contrary, we can find $e-$, $μ-$ and $τ-$leptogenesis scenarios in which the cosmological CP violation and low energy CP violation measurable via neutrino oscillations are very closely related to each other. By determining the allowed ranges of the parameters in the models, we predict the sizes of CP violation in neutrino oscillation and $|V_{e3}^{MNS}|$. Finally, the leptonic unitarity triangles are reconstructed.

hep-ph↗