arXiv subjects

Shinji Maedan

Publications and source records attributed to Shinji Maedan.

7 recordsLinked to original sources

arXiv2021

Vacuum angle theta in a strongly interacting hidden sector and its effect

Introducing a vacuum angle $\theta_h$ in a strongly interacting hidden sector like QCD, we study how $\theta_h$ affects physical quantities in a scale invariant extension of the standard model with that hidden sector. In this model the dynamical chiral symmetry breaking occurs in the hidden sector and generates a scale $ \vert \langle {\bar q} q \rangle \vert $ which triggers electroweak symmetry breaking. We find that the expression for a vacuum expectation value of the Higgs field depends on $\theta_h$, while the condition which determines the Higgs particle mass does not. This model contains the hidden-sector pions $\pi^0$ and $\pi^{\pm}$ which are candidates for cold dark matter, and we find the mass difference between the hidden-sector $\pi^0$ and $\pi^{\pm}$ will not be negligible for $\theta_h \approx \pi$.

hep-ph↗

arXiv2019

Influence of EOS on compact star made of hidden sector nucleons

We study compact star made of degenerate hidden sector nucleons which will be a candidate for cold dark matter. A hidden sector like QCD is considered, and as the low energy effective theory we take (hidden sector) $ SU(2) $ chiral sigma model including hidden sector vector meson. With the mean field approximation, we find that one can treat the equation of state (EOS) of our model analytically by introducing a variable which depends on the Fermi momentum. The EOS is specified by the two parameters $ C'_{/sigma} $,$ C'_{/omega} $, and we discuss how these parameters affect on the mass-radius relation for compact star as well as on the EOS. The dependence of the maximum stable mass of compact stars on the parameter $ C'_{/sigma} $ will also be discussed.

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arXiv2016

Predicted value of $0 \, \nu \beta \beta$-decay effective Majorana mass with error of lightest neutrino mass

Assuming that the lightest neutrino mass $ m_0 $ is measured, we study the influence of error of the measured $ m_0 $ on the uncertainty of the predicted value of the neutrinoless double beta decay ($0 \, \nu \beta \beta$) effective Majorana mass $ \vert m_{ee} \vert $. The error of the predicted value of effective Majorana mass $ \sigma ( \vert m_{ee} \vert ) $ due to the error $ \sigma (m_0) $ is obtained by use of the propagation of errors. We investigate in detail how $ \sigma ( \vert m_{ee} \vert ) $ behaves when the Majorana phases $ \beta $ and $ \alpha $ change, and also when the size of the lightest neutrino mass changes. It is shown that $ \sigma ( \vert m_{ee} \vert ) $ does not exceed $ \sigma (m_0) $, and that the minimum value of $ \sigma ( \vert m_{ee} \vert ) $ in the $ \beta - \alpha $ plane can be zero if the size of $ m_0 $ is rather small. In the normal mass ordering case, the maximum value of $ \sigma ( \vert m_{ee} \vert ) $ in the $ \beta - \alpha $ plane becomes about $ 0.68 \, \sigma (m_0) $ if $ m_0 (= m_1 ) $ is very small, while in the inverted mass ordering case, it becomes about $ 0.02 \, \sigma (m_0) $ if $ m_0 (= m_3 ) $ is very small. By use of the calculated $ \sigma ( \vert m_{ee} \vert ) $, we also discuss the minimum condition for the relative error of the lightest neutrino mass to raise the possibility of obtaining the information on $ \beta $ and $ \alpha $.

hep-ph↗

arXiv2014

Analytically expressed constraint on two Majorana phases in neutrinoless double beta decay

We assume that neutrinoless double beta decay is caused by the exchange of three light Majorana neutrinos. Under this assumption, we obtain, by the method of perturbation, the equation representing the isocontour of effective Majorana mass which is the function of two CP-violating Majorana phases. The equation representing the isocontour (constraint equation between two Majorana phases) is expressed analytically by six parameters: two lepton mixing angles, two kinds of neutrino mass squared differences, lightest neutrino mass scale, and the effective Majorana mass. We discuss how the constraint equation between two Majorana phases changes when the lightest neutrino mass scale is varied.

hep-ph↗

arXiv2009

Influence of current mass on the spatially inhomogeneous chiral condensate

It is known that, in the chiral limit, spatially inhomogeneous chiral condensate occurs in the Nambu-Jona-Lasinio (NJL) model at finite density within a mean-field approximation. We study here how an introduction of current quark mass affects the ground state with the spatially inhomogeneous chiral condensate. Numerical calculations show that, even if the current quark mass is introduced, the spatially inhomogeneous chiral condensate can take place. In order to obtain the ground state, the thermodynamic potential is calculated with a mean-field approximation. The influence of finite current mass on the thermodynamic potential consists of following two parts. One is a part coming from the field energy of the condensate, which favors inhomogeneous chiral condensate. The other is a part coming from the Dirac sea and the Fermi sea, which favors homogeneous chiral condensate. We also find that when the spatially inhomogeneous chiral condensate occurs, the baryon number density becomes spatially inhomogeneous.

hep-ph↗

arXiv2006

Spin polarization and chiral symmetry breaking at finite density

We investigate the possibility of the spin polarization of quark matter at zero temperature and moderate baryon density.The Nambu-Jona-Lasinio (NJL) model including interactions in vector and axial-vector channel (coupling constant $G_2$) as well as scalar and pseudoscalar channel (coupling constant $G_1$) is used, and the self consistent equations for the spin polarization and chiral condensate are solved numerically in the framework of the Hartree approximation. Numerical calculations show that in the one flavor model the spin polarization is possible at finite density if the ratio $G_2/G_1$ is larger than O(1).We find that the interplay between the spin polarization and the chiral symmetry plays an important role.If the chemical potential of quarks reaches a certain finite value, the spin polarization begins to occur because the quark still has relatively large dynamical mass, which is generated by spontaneous chiral symmetry breaking.On the other hand, when the spin polarization occurs, it operates to lower the dynamical quark mass a little.If one increases the chemical potential furthermore, the spin polarization becomes weaker and finally disappears because the dynamical quark mass is reduced by restoring gradually the chiral symmetry.

hep-ph↗

arXiv2004

Space-time evolution of a condensate in the interaction representation

The space-time evolution of an inhomogeneous as well as homogeneous condensate is studied. We use the $ λϕ^4 $ model and adopt the interaction representation in which the particle picture of the field $ϕ$ with mass $m$ is definitely obtained. As the initial condition, a coherent state is assumed. In the case of the homogeneous condensate, the amplitude of it grows continuously with time and the perturbative calculation breaks down for large time. On the other hand, in the case of the inhomogeneous condensate with a finite initial size $\sim R$, the behavior of it is so different from that of the homogeneous one. For $0< t < m R^2/2 $, the growth of the amplitude of the inhomogeneous condensate at the origin $ ({\boldsymbol x}={\bf 0}) $ is slowed down compared with that of the homogeneous one, and the contribution of the interaction term $ (λ/4) :ϕ^4: $ is restricted to the small region around the origin of the condensate. For the late time, $ t > m R^2/2 $, the condensate spreads into space.

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