arXiv subjects

Daiji Kimura

Publications and source records attributed to Daiji Kimura.

14 recordsLinked to original sources

arXiv2023

Super Restoration of Chiral Symmetry in Massive Four-Fermion Interaction Models

The chiral symmetry is explicitly and spontaneously broken in a strongly interacting massive fermionic system. We study the chiral symmetry restoration in massive four-fermion interaction models with increasing temperature and chemical potential. At high temperature and large chemical potential, we find the boundaries where the spontaneously broken chiral symmetry can be fully restored in the massive Gross--Neveu model. We call the phenomenon super restoration. The phase boundary is obtained analytically and numerically. In the massive Nambu--Jona-Lasinio model, it was found that whether super restoration occurs depends on regularizations. We also evaluate the behavior of the dynamical mass and show the super restoration boundaries on the ordinary phase diagrams.

hep-ph↗

arXiv2018

Analysis of Dalitz decays with intrinsic parity violating interactions in resonance chiral perturbation theory

Observables of light hadron decays are analyzed in a model of chiral Lagrangian which includes resonance fields of vector mesons. In particular, transition form factors are investigated for Dalitz decays of $V\to Pl^+l^-$ and $P\to γl^+l^-$ $(V=1^-, P=0^-)$. Moreover, the differential decay width of $P\to π^+π^-γ$ and the partial widths of $P\to2γ, V\to Pγ, η^\prime\to Vγ, ϕ(1020)\toω(782)π^0$ and $V\to 3P$ are also calculated. In this study, we consider a model which contains octet and singlet fields as representation of $SU(3)$. As an extension of chiral perturbation theory, we include 1-loop ordered interaction terms. For both pseudoscalar and vector meson, we evaluate mixing matrices in which isospin/$SU(3)$ breaking is taken into account. Furthermore, intrinsic parity violating interactions are considered with singlet fields. For parameter estimation, we carry out $χ^2$ fittings in which a spectral function of $τ$ decays, vector meson masses, decay widths of $V\to Pγ$ and transition form factor of $V\to Pl^+l^-$ are utilized as input data. Using the estimated parameter region in the model, we give predictions for decay widths and transition form factors of intrinsic parity violating decays. As further model predictions, we calculate the transition form factors of $ϕ(1020)\to π^0l^+l^-$ and $η^\prime\toγl^+l^-$ in the vicinity of resonance regions, taking account of the contribution for intermediate $ρ(770)$ and $ω(782)$.

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arXiv2015

Study of anomalous tau lepton decay using chiral Lagrangian with vector mesons

An intrinsic parity violating hadronic tau lepton decay is investigated. $τ\to ππην$ is the process in which the dominant contribution to the amplitude is due to the intrinsic parity violation. To predict the hadronic invariant mass spectra and to compare them with experimental data, we extend the chiral Lagrangian with vector mesons so that it incorporates the intrinsic parity violating terms and $ϕ$ and $η^\prime$ mesons. The coefficients of the intrinsic parity violating terms will be determined by fitting the branching fractions for $V^I \rightarrow P γ$, $V^I \rightarrow 3 P$ and $P \to V^I γ$ where $V^I$ denotes vector mesons $1^-$ and $P$ denotes pseudo-scalar mesons $0^-$.

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arXiv2014

Study of an anomalous tau lepton decay using a chiral Lagrangian with vector mesons

The hadronic tau decay $τ^- \to ν_τηπ^- π^0$ occurs through V-A weak current. In this decay mode, the vector current contribution is intrinsic parity violating and the axial current contribution is G parity violating. The latter contribution is suppressed due to tiny isospin breaking. We have computed both vector and axial vector form factors using a chiral Lagrangian with vector mesons including the effect of isospin breaking and intrinsic parity violation. A numerical result of the invariant mass distribution is shown and the structure of $ρ$ resonance can be seen in the distribution with respect to $M_{π^- π^0}$.

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arXiv2013

A numerical evaluation of vacuum polarization tensor in constant external magnetic fields

Hattori-Itakura have recently derived the full Landau-level summation form for the photon vacuum polarization tensor in constant external magnetic fields at the one-loop level. The Landau-level summation form is essential when the photon momentum exceeds the threshold of the pair creation of charged particles in a magnetic field stronger than the squared mass of the charged particle. The tensor has three different form factors depending on the tensor direction with respect to the external magnetic field. The renormalization is nontrivial because these form factors are expressed in terms of double or triple summation forms. We give a numerical UV subtraction method which can be applied to numerically evaluate the form factors in constant external magnetic fields. We numerically investigate the photon vacuum polarization tensor in the form of the Landau-level summation and estimate the systematic errors coming from truncation of the Landau-level summation in a parameter region realized in heavy ion collision experiments. We find that the error is practically controllable at an $O(10^{-2})$ level for electrons and muons in strong magnetic fields expected in heavy ion collisions in the experimentally feasible kinematic parameter regions.

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arXiv2012

The form factors for hadronic tau decay using background field method

In the two body hadronic tau decays, such as tau->to K pi (eta)nu, vector mesons play important role. Belle and Babar measured hadronic invariant mass spectrum of tau -> K pi nu decay. To compare the spectrum with theoretical prediction, we develop the chiral Lagrangian with vector mesons in Kimura:2012nx. We compute the form factors of the hadronic tau decay taking account of the quantum corrections of Nambu Goldstone bosons. We also show how to renormalizethe divergence of the Feynman diagrams with arbitrary number of loops and determine the counterterms within one loop using background field method.In this report, we discuss the renormalization of Kimura:2012nx by considering the one loop Feynman diagrams.

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arXiv2012

CP violation of Extended Higgs sector and Its impact on D^0 -> mu^+ mu^- decay

We study the impact of the CP violation of the extra Higgs sector on $D^0$ decay. The CP even and CP odd neutral Higgs mixing of the two Higgs doublet model is studied and we show how the CP violating effect of the mixing may lead to the longitudinal muon polarization asymmetry of $D^0 \to μ^+ μ^-$. The asymmetry of the short-distance contribution is sensitive to the CP violating phase of the extended Higgs sector.

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arXiv2010

Charged Higgs Flavor Changing Current in tau^- to nu_X K^- pi^0

We study the effect of flavor changing charged current(FCCC) of lepton sector in the hadronic tau decays, tau \to nu_X K^- pi^0 (X=e,mu). In general two Higgs doublet model, the lepton flavor changing neutral current (FCNC) arises in the charged lepton sector and contributes to the process such as tau \to mu mu^+ mu^- and tau \to mu(e) P^0 where P^0=pi^0,eta, eta'. We derive a relation between the FCCC in charged Higgs boson and the FCNC due to the neutral Higgs boson. Then by using the recent experimental upper bound on FCNC of tau \to l_X eta (pi^0) (l_X=e,mu) processes, we study how large the effect of FCCC could be in the process tau \to nu_X K pi decays. We also report the preliminary result on the form factor calculations of tau \to K pi nu decays and the hadronic invariant mass distribution.

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arXiv2009

CP violation in tau decays

CP violation of the charged lepton sector has not been found yet. Tau is a unique charged lepton which can decay into hadrons. In this talk, we argue what kind of new physics can be studied with CP violation of tau lepton decays. We also disucuss how to handle hadronic final state interactions for a prediction of the direct CP violation.

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arXiv2008

CP violation of tau -> K pi(eta, eta') nu decays

We study direct CP violation of tau -> K pi(eta,eta')nu decays. By studying the forward and backward asymmetry, the interference of L=0 and L=1 amplitudes of the hadronic system can be extracted. By including the scalar and vector mesons into the chiral Lagrangian, we compute the form factors which correspond to L=0 and L=1 angular momentum state of the hadronic system. We include real and imaginary parts of the one loop corrections to the self-energies of the scalar and vector mesons. The direct CP violation of the forward and backward asymmetry is computed using a two Higgs doublet model in which a new CP violating phase is introduced. We show how the CP violation of the forward and the backward asymmetry may depend on the new CP violating phase and the strong phase of the form factors.

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arXiv2007

Phase structure of NJL model with finite quark mass and QED correction

We study QED corrections to the chiral symmetry breaking in Nambu-Jona-Lasinio (NJL) model with two flavors of quarks. In the model the isospin symmetry is broken by differences of the current quark masses and the electromagnetic charges between up and down quarks. In the leading order of the 1/N expansion we calculate the effective potential of the model with one-loop QED corrections. Evaluating the effective potential, we study an influence of the isospin symmetry breaking on the orientation of chiral symmetry breaking. The current quark mass has an important contribution for the orientation of chiral symmetry breaking.

hep-ph↗

arXiv2004

Proper-Time Formalism in a Constant Magnetic Field at Finite Temperature and Chemical Potential

We investigate scalar and spinor field theories in a constant magnetic field at finite temperature and chemical potential. In an external constant magnetic field the exact solution of the two-point Green functions are obtained by using the Fock-Schwinger proper-time formalism. We extend it to the thermal field theory and find the expressions of the Green functions exactly for the temperature, the chemical potential and the magnetic field. For practical calculations the contour of the proper-time integral is carefully selected. The physical contour is discussed in a constant magnetic field at finite temperature and chemical potential. As an example, behavior of the vacuum self-energy is numerically evaluated for the free scalar and spinor fields.

hep-ph↗

arXiv2004

NJL Model at Finite Chemical Potential in a Constant Magnetic Field

We investigate the influence of an external magnetic field on chiral symmetry breaking in the Nambu-Jona-Lasinio (NJL) model at finite temperature and chemical potential. According to the Fock-Schwinger proper-time method, we calculate the effective potential in the leading order of the $1/N_c$ expansion. The phase boundary dividing the symmetric phase and the broken phase is illustrated numerically. A complex behavior of the phase boundary is found for large chemical potential.

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arXiv2004

Four-fermion Interaction Model in a Constant Magnetic Field at Finite Temperature and Chemical Potential

We investigate an influence of an external magnetic field on chiral symmetry breaking in a four-fermion interaction model at finite temperature and chemical potential. By using the Fock-Schwinger proper-time method, we calculate the effective potential for the four-fermion interaction model at the leading order of the $1/N_c$ expansion. A phase structure of the chiral symmetry breaking is shown on $T$-$μ$, $H$-$T$ and $μ$-$H$ planes. The external magnetic field modifies the phase structure. It is found that a new phase appears for a large chemical potential.

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