arXiv subjects

Takuya Morozumi

Publications and source records attributed to Takuya Morozumi.

At least 37 records · Page 2Linked to original sources

arXiv2018

Phenomenological Aspects of Possible Vacua of a Neutrino Flavor Model

We discuss a supersymmetric model with discrete flavor symmetry $A_4\times Z_3$. The additional scalar fields which contribute masses of leptons in the Yukawa terms are introduced in this model. We analyze their scalar potential and find that they have various vacuum structures. We show the relations among 24 different vacua and classify them into two types. We derive expressions of the lepton mixing angles, Dirac CP violating phase and Majorana phases for the two types. The model parameters which are allowed by the experimental data of the lepton mixing angles are different for each type. We also study the constraints on the model parameters which are related to Majorana phases. The different allowed regions of the model parameters for the two types are shown numerically for a given region of two combinations of the CP violating phases.

hep-ph↗

arXiv2016

Creation and evolution of particle numberasymmetry in an expanding universe

We introduce a model which may generate particle number asymmetry in an expanding Universe. The model includes CP violating and particle number violating interactions. The model consists of a real scalar field and a complex scalar field. Starting with an initial condition specified by a density matrix, we show how the asymmetry is created through the interaction and how it evolves at later time. We compute the asymmetry using non-equilibrium quantum field theory and as a first test of the model, we study how the asymmetry evolves in the flat limit.

hep-ph↗

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 $0^-$.

hep-ph↗

arXiv2015

Precise discussion on T-asymmetry with B-meson decays

Through $B\bar{B}$ mixing system, one can construct an asymmetry which naively seems to be a time reversal (T) odd quantity. In this article, the two processes $(\mathrm{a})\: B_-\rightarrow \bar{B^0}$ and $(\mathrm{b})\: \bar{B^0}\rightarrow B_-$ are used to construct the event number asymmetry. The CP violation of Kaon system denoted as $ε_K$ contributes to observables and we evaluate the contribution from $ε_K$ explicitly. The asymmetry is formulated with phase convention independent parameters which are invariant under redefinition of phase of quark fields. The overall factors of the time dependent decay rates are taken into account in this article. Furthermore, we suggest conditions for the asymmetry to be a T-odd quantity. The one of such conditions arises due to the difference of overall factors which form the asymmetry.

hep-ph↗

arXiv2015

Precise Discussion of Time-Reversal Asymmetries in B-meson decays

BaBar collaboration announced that they observed time reversal (T) asymmetry through $B$ meson system. In the experiment, time dependencies of two distinctive processes, $B_- \rightarrow \bar{B^0}$ and $\bar{B^0}\rightarrow B_-$($-$ expresses CP value) are compared with each other. In our study, we examine event number difference of these two processes. In contrast to the BaBar asymmetry, the asymmetry of events number includes the overall normalization difference for rates. Time dependence of the asymmetry is more general and it includes terms absent in one used by BaBar collaboration. Both of the BaBar asymmetry and ours are naively thought to be T-odd since two processes compared are related with flipping time direction. We investigate the time reversal transformation property of our asymmetry. Using our notation, one can see that the asymmetry is not precisely a T-odd quantity, taking into account indirect CP and CPT violation of K meson systems. The effect of $ε_K$ is extracted and gives rise to $\mathcal{O}(10^{-3})$ contribution. The introduced parameters are invariant under rephasing of quarks so that the coefficients of our asymmetry are expressed as phase convention independent quantities. Some combinations of the asymmetry enable us to extract parameters for wrong sign decays of $B_d$ meson, CPT violation, etc. We also study the reason why the T-even terms are allowed to contribute to the asymmetry, and find that several conditions are needed for the asymmetry to be a T-odd quantity.

hep-ph↗

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 $M_{π^- π^0}$.

hep-ph↗

arXiv2014

Time variation of particle and anti-particle asymmetry in an expanding universe

Particle number violating interactions wash out the primordial asymmetry of particle number density generated by some interaction satisfying Sakharov conditions for baryogenesis. In this paper, we study how the primordial asymmetry evolves in time under the presence of particle number violating interactions and in the environment of expanding universe. We introduce a complex scalar model with particle number violating mass terms and calculate the time evolution of the particle number density with non-equilibrium quantum field theory. We show how the time evolution of the number density depends on parameters, including the chemical potential related with the particle number, temperature, size of the particle number violating mass terms, and the expansion rate of the universe. Depending upon whether the chemical potential is larger or smaller than the rest mass of the scalar particle, behaviors of the number density are very different to each other. When the chemical potential is smaller than the mass, the interference among the contribution of oscillators with various momenta reduces the number density in addition to the dilution due to the expansion of universe. In opposite case, the oscillation of the particle number density lasts for a long time and the cancellation due to the interference does not occur.

hep-ph↗

arXiv2014

Quantum correction to tiny vacuum expectation value in two Higgs doublet model for Dirac neutrino mass

We study a Dirac neutrino mass model of Davidson and Logan. In the model, the smallness of the neutrino mass is originated from the small vacuum expectation value of the second Higgs of two Higgs doublets. We study the one loop effective potential of the Higgs sector and examine how the small vacuum expectation is stable under the radiative correction. By deriving formulae of the radiative correction, we numerically study how large the one loop correction is and show how it depends on the quadratic mass terms and quartic couplings of the Higgs potential. The correction changes depending on the various scenarios for extra Higgs mass spectrum.

hep-ph↗

arXiv2014

Charged Higgs and Neutral Higgs pair production of weak gauge bosons fusion process in e+ e- collision

In this paper, we study the pair production and their decays of the Higges in the neutrinophilic Higgs two doublet model. The pair production occurs through W and Z gauge bosons fusion process. In the neutrinophilic model, the vacuum expectation value (VEV) of the second Higgs doublet is small and is proportional to the neutrino mass. The smallness of VEV is associated with the approximate global U(1) symmetry which is slightly broken. Therefore, there is a suppression factor for the U(1) charge breaking process. The second Higgs doublet has U(1) charge and its single production from the gauge boson fusion violates the U(1) charge conservation and is suppressed strongly to occur. In contrast to the single production, the pair production of the Higgses conserves U(1) charge and the approximate symmetry does not forbid it. To search for the pair productions in collider experiment,we study the production cross section of a pair of the charged Higgs and neutral Higgs bosons in e+ e- collision with center of energy from 600 (GeV) to 2000 (GeV). The total cross section varies from 10^{-4}(fb) to 10^{-3}(fb) for degenerate (200 GeV) charged and neutral Higgses mass case. The background process to the signal is gauge bosons pair W + Z production and their decays. We show the signal over background ratio is about 2% ~ 3% by combining the cross section ratio with ratios of branching fractions.

hep-ph↗

arXiv2013

Quark sector CP violation of the universal seesaw model

We study the CP violation of universal seesaw model, especially its quark sector. The model is based on SU(2)_L \times SU(2)_R \times U(1)_{Y^\prime}. In order to count the number of parameters in quark sector, we use the degree of freedom of weak basis transformation. For N(3)-generation model, the number of CP violating phase in quark sector is identified as 3N^2-3N+1 (19). We also construct nineteen CP violating weak basis invariants of Yukawa coupling matrices and SU(2) singlet quark mass matrices in the three-generation universal seesaw model. The quark interaction terms induced by neutral currents are given as an exact formula. Both of the charged current and the neutral current are expressed in terms of the mass basis by finding the transformations from weak basis to mass basis. Finally, we calculate the mixing matrix element approximately assuming that the SU(2)_R breaking scale v_R is much larger than the electro-weak breaking scale v_L.

hep-ph↗

arXiv2012

The pair production of Charged and Neutral Higgs bosons in W and Z gauge boson fusion process

We study the signatures of a two Higgs doublet model of Davidson and Logan. The model includes an extra Higgs doublet with the vacuum expectation value (VEV) much smaller than the one of the standard model like Higgs. The smaller VEV is related to the origin of the small neutrino mass in the two Higgs doublet model. In the model, a single non-standard model like Higgs production of weak gauge boson fusion is suppressed due to the smallness of the vacuum expectation value. In contrast to the single Higgs production, the cross section of the Higgs pair production due to gauge boson fusion is not suppressed. Using the model, we compute the charged Higgs and neutral Higgs pair production cross section in W Z annihilation channel. In the two Higgs doublet model, the charged Higgs H^+ decays into a pair of the charged anti-lepton and right-handed neutrino. The neutral Higgs boson decays into right-handed neutrino and left-handed anti-neutrino pair which is invisible. A single charged anti-lepton and three neutrinos are the products of the subsequent decays of the charged Higgs and the neutral Higgs. W Z pair production gives the background for the signal through the decays W^+ ->nu l^+ and Z -> nu nubar. By multiplying the charged and neutral Higgses production cross section with the lepton flavor specific decay branching fractions of charged Higgs, we define a measurement which characterizes the present model. We numerically compute the measurement and find the sizable deviation from the standard model prediction.

hep-ph↗

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.

hep-ph↗

arXiv2012

Particle number production and time variation with non-equilibrium quantum field theory

We study the particle number production and its time variation using non-equilibrium quantum field theory. We study the model proposed by Hotta et.al. \cite{Hotta:2012hi} for particle number production with a heavy neutral scalar and a light complex scalar. The interaction Lagrangian contains CP violating phase and particle number violating interaction among the scalars. The particle number violating mass term is also introduced, which splits a complex scalar into two real scalars with small non-degenerate mass. Therefore, the term generates particle and anti-particle mixing. We study the long time behavior of the particle number production rate.

hep-ph↗

arXiv2012

Contribution from the interaction Hamiltonian to the expectation value of particle number with the non-equilibrium quantum field theory

We develop the method analyzing particle number non-conserving phenomena with non-equilibrium quantum field theory. In this study, we consider a CP violating model with interaction Hamiltonian that breaks particle number conservation. To derive the quantum Boltzmann equation for the particle number, we solve Schwinger-Dyson equation, which are obtained from two particle irreducible closed-time-path (2PI CTP) effective action. In this calculation, we show the contribution from interaction Hamiltonian to the time evolution of expectation value of particle number.

hep-th↗

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.

hep-ph↗

arXiv2010

Effects of Large Threshold Corrections in Supersymmetric Type-I Seesaw Model

We investigate lepton flavor violating (LFV) radiative processes and the relic abundance of neutralino dark matter in supersymmetric type-I seesaw model. We carefully derive threshold corrections to the flavor off-diagonal elements of slepton mass matrix and up-type Higgs mass squared and find that they can be large in the case of large $B_N^0$. We examine how the branching ratios of LFV radiative decays and the relic abundance of neutralino dark matter can be significantly affected by the large threshold corrections. Soft scalar mass squared parameter of up-type Higgs scalar is also affected by the threshold corrections. Since the higgsino mass depends on the mass parameter for up-type Higgs, the LFV processes and the relic abundance of the neutralino dark matter are correlated with each other. We show that there are parameter regions where the predictions of the relic abundance of neutralino dark matter are consistent with WMAP observation and the branching ratios of LFV radiative decays are predicted to be testable in future experiments. We find that the masses of scalar supersymmetric particles are not necessarily small so that the branching ratios of LFV decays can be testable in future experiment, which is distinctive feature of this scenario.

hep-ph↗

arXiv2010

Threshold corrections to the radiative breaking of electroweak symmetry and neutralino dark matter in supersymmetric seesaw model

We study the radiative electroweak symmetry breaking and the relic abundance of neutralino dark matter in the supersymmetric type I seesaw model. In this model, there exist threshold corrections to Higgs bilinear terms coming from heavy singlet sneutrino loops, which make the soft supersymmetry breaking (SSB) mass for up-type Higgs shift at the seesaw scale and thus a minimization condition for the Higgs potential is affected. We show that the required fine-tuning between the Higgsino mass parameter mu and the SSB mass for up-type Higgs may be reduced at the electroweak scale, due to the threshold corrections. We also present how the parameter mu depends on the SSB B-parameter for heavy singlet sneutrinos. Since the property of neutralino dark matter is quite sensitive to the size of mu, we discuss how the relic abundance of neutralino dark matter is affected by the SSB B-parameter. Taking the SSB B-parameter of order of a few hundreds TeV, the required relic abundance of neutralino dark matter can be correctly achieved. In this case, dark matter is a mixture of bino and Higgsino, under the condition that gaugino masses are universal at the grand unification scale.

hep-ph↗

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.

hep-ph↗