Searcharxiv⌕ Search

arXiv subjects

Michio Hashimoto

Publications and source records attributed to Michio Hashimoto.

At least 37 records · Page 2Linked to original sources
arXiv2007

Meissner screening masses in gluonic phase

A numerical analysis for the Meissner mass in the simplest gluonic phase (the minimal cylindrical gluonic phase II) is performed in the framework of the gauged Nambu-Jona-Lasinio model with cold two-flavor quark matter. We derive Meissner mass formulae without using the numerical second derivative. It is revealed that the gapless mode yields a characterized contribution to the Meissner mass. We also find that there are large and positive contributions from the tree gluon potential term to the transverse modes of gluons. It is shown that the simplest gluonic phase resolves the chromomagnetic instability in a rather wide region.

hep-ph↗
arXiv2007

Gluonic phases and phase diagram in neutral two flavor dense QCD

A numerical analysis of several phases in the cold neutral two flavor dense quark matter is realized. In the analysis, besides the normal, single plane wave LOFF, and color superconducting 2SC/g2SC phases, we also include two gluonic phases (the gluonic cylindrical phase II and the gluonic color-spin locked one). It is shown that these two gluonic phases are dynamically realized and, on the basis of this analysis, the phase diagram with respect to the coupling strength in this medium is suggested. In particular, it is shown that the gluonic phases are energetically favorable in a wide region of the parameter space. On the other hand, there also exists a window where the LOFF phase is stable. The 2SC state and the normal one are realized in the strong and weak coupling regimes, respectively, as was expected.

hep-ph↗
arXiv2007

Gluonic phases, vector condensates, and exotic hadrons in dense QCD

We study the dynamics in phases with vector condensates of gluons (gluonic phases) in dense two-flavor quark matter. These phases yield an example of dynamics in which the Higgs mechanism is provided by condensates of gauge (or gauge plus scalar) fields. Because vacuum expectation values of spatial components of vector fields break the rotational symmetry, it is naturally to have a spontaneous breakdown both of external and internal symmetries in this case. In particular, by using the Ginzburg-Landau approach, we establish the existence of a gluonic phase with both the rotational symmetry and the electromagnetic U(1) being spontaneously broken. In other words, this phase describes an anisotropic medium in which the color and electric superconductivities coexist. It is shown that this phase corresponds to a minimum of the Ginzburg-Landau potential and, unlike the two-flavor superconducting (2SC) phase, it does not suffer from the chromomagnetic instability. The dual (confinement) description of its dynamics is developed and it is shown that there are light exotic vector hadrons in the spectrum, some of which condense. Because most of the initial symmetries in this system are spontaneously broken, its dynamics is very rich.

hep-ph↗
arXiv2006

Manifestation of Instabilities in Nambu-Jona-Lasinio type models

We study a Nambu-Jona-Lasinio (NJL) type model with two-flavor quark matter in $β$-equilibrium. It turns out that the system develops instabilities in the dispersion relations of the diquark fields, i.e., the velocity squared $v^2$ becomes negative in a certain region of the electron chemical potential. The critical point is the same as that of the chromomagnetic instability. The results imply the existence of spatially inhomogeneous diquark condensates in the genuine vacuum. We also discuss gauge equivalent classes between the inhomogeneous diquark condensates and gluon condensates.

hep-ph↗
arXiv2006

Collective excitations, instabilities, and ground state in dense quark matter

We study the spectrum of light plasmons in the (gapped and gapless) two-flavor color superconducting phases and its connection with the chromomagnetic instabilities and the structure of the ground state. It is revealed that the chromomagnetic instabilities in the 4-7th and 8th gluonic channels correspond to two very different plasmon spectra. These spectra lead us to the unequivocal conclusion about the existence of gluonic condensates (some of which can be spatially inhomogeneous) in the ground state. We also argue that spatially inhomogeneous gluonic condensates should exist in the three-flavor quark matter with the values of the mass of strange quark corresponding to the gapless color-flavor locked state.

hep-ph↗
arXiv2005

Neutral Larkin--Ovchinnikov--Fulde--Ferrell state and chromomagnetic instability in two-flavor dense QCD

In two-flavor dense quark matter, we describe the dynamics in the single plane wave Larkin--Ovchinnikov--Fulde--Ferrell (LOFF) state satisfying the color and electric neutrality conditions. We find that because the neutral LOFF state itself suffers from a chromomagnetic instability in the whole region where it coexists with the (gapped/gapless) two-flavor superconducting (2SC/g2SC) phases, it cannot cure this instability in those phases. This is unlike the recently revealed gluonic phase which seems to be able to resolve this problem.

hep-ph↗
arXiv2005

Gluonic phase in neutral two-flavor dense QCD

In the Ginzburg-Landau approach, we describe a new phase in neutral two-flavor quark matter in which gluonic degrees of freedom play a crucial role. We call it a gluonic phase. In this phase gluonic dynamics cure a chromomagnetic instability in the 2SC solution and lead to spontaneous breakdown of the color gauge symmetry, the electromagnetic U(1), and the rotational SO(3). In other words, the gluonic phase describes an anisotropic medium in which the color and electric superconductivities coexist. Because most of the initial symmetries in this system are spontaneously broken, its dynamics is very rich.

hep-ph↗
arXiv2005

Noncommutativity vs. Transversality in QED in a strong magnetic field

Quantum electrodynamics (QED) in a strong constant magnetic field is investigated from the viewpoint of its connection with noncommutative QED. It turns out that within the lowest Landau level (LLL) approximation the 1-loop contribution of fermions provides an effective action with the noncommutative U(1)_{NC} gauge symmetry. As a result, the Ward-Takahashi identities connected with the initial U(1) gauge symmetry are broken down in the LLL approximation. On the other hand, it is shown that the sum over the infinite number of the higher Landau levels (HLL's) is relevant despite the fact that each contribution of the HLL is suppressed. Owing to this nondecoupling phenomenon the transversality is restored in the whole effective action. The kinematic region where the LLL contribution is dominant is also discussed.

hep-th↗
arXiv2005

Topcolor breaking through boundary conditions

The nontrivial boundary conditions (BC's) for the Topcolor breaking are investigated in the context of the TeV-scale extra dimension scenario. In the gauge symmetry breaking mechanism via the BC's we do not need to incorporate a dynamical mechanism for the Topcolor breaking into the model. Moreover, the Topcolor breaking can be realized without introducing explicitly a (composite) scalar field. We present a six dimensional model where the top and bottom quarks in the bulk have the Topcolor charge while the other quarks in the bulk do not. We also put the electroweak gauge interaction in the six dimensional bulk. The bottom quark condensation is naturally suppressed owing to the power-like running of the bulk U(1)_Y interaction, so that only the top condensation is expected to take place. We explore such a possibility based on the ladder Schwinger-Dyson equation and show the cutoff to make the model viable.

hep-ph↗
arXiv2005

Topcolor model in extra dimensions and nontrivial boundary conditions

The nontrivial boundary conditions for the Topcolor breaking are investigated in the context of the TeV-scale extra dimension scenario. We present a six dimensional model where the top and bottom quarks in the bulk have the Topcolor charge while the other quarks in the bulk do not. We also put the electroweak gauge interaction in the six dimensional bulk. Then the bottom quark condensation is naturally suppressed owing to the power-like running of the bulk $U(1)_Y$ interaction, so that only the top condensation is expected to take place. We explore such a possibility based on the ladder Schwinger-Dyson equation and show the cutoff to make the model viable.

hep-ph↗
arXiv2005

Nondecoupling phenomena in QED in a magnetic field and noncommutative QED

The dynamics in QED in a strong constant magnetic field and its connection with the noncommutative QED are studied. It is shown that in the regime with the lowest Landau level (LLL) dominance the U(1) gauge symmetry in the fermion determinant is transformed into the noncommutative $U(1)_{nc}$ gauge symmetry. In this regime, the effective action is intimately connected with that in noncommutative QED and the original U(1) gauge Ward identities are broken (the LLL anomaly). On the other hand, it is shown that although a contribution of each of an infinite number of higher Landau levels is suppressed in an infrared region, their cumulative contribution is not (a nondecoupling phenomenon). This leads to a restoration of the original U(1) gauge symmetry in the infrared dynamics. The physics underlying this phenomenon reflects the important role of a boundary dynamics at spatial infinity in this problem.

hep-th↗
arXiv2004

Top mode standard model and extra dimensions

We perform the most attractive channel (MAC) analysis in the top mode standard model with TeV-scale extra dimensions, where the standard model gauge bosons and the third generation of quarks and leptons are put in D(=6,8,...) dimensions. In order to make the scenario viable, only the attractive force of the top condensate should exceed the critical coupling, while other channels such as the bottom and tau condensates should not. It turns out that the top condensate can be the MAC for D=8, whereas the tau condensation is favored for D=6. On the basis of the renormalization group equations for the top Yukawa and Higgs quartic couplings, we predict masses of the top quark and the Higgs boson for D=8 as m_t=172-175 GeV and m_H=176-188 GeV, respectively.

hep-ph↗
arXiv2004

Gauged Nambu-Jona-Lasinio model with extra dimensions

We investigate phase structure of the D (> 4)-dimensional gauged Nambu-Jona-Lasinio (NJL) model with $δ(=D-4)$ extra dimensions compactified on TeV scale, based on the improved ladder Schwinger-Dyson (SD) equation in the bulk. We assume that the bulk running gauge coupling in the SD equation for the SU(N_c) gauge theory with N_f massless flavors is given by the truncated Kaluza-Klein effective theory and hence has a nontrivial ultraviolet fixed point (UVFP). We find the critical line in the parameter space of two couplings, the gauge coupling and the four-fermion coupling, which is similar to that of the gauged NJL model with fixed (walking) gauge coupling in four dimensions. It is shown that in the presence of such walking gauge interactions the four-fermion interactions become ``nontrivial'' even in higher dimensions, similarly to the four-dimensional gauged NJL model. Such a nontriviality holds only in the restricted region of the critical line (``nontrivial window'') with the gauge coupling larger than a non-vanishing value (``marginal triviality (MT)'' point), in contrast to the four-dimensional case where such a nontriviality holds for all regions of the critical line except for the pure NJL point. In the nontrivial window the renormalized effective potential yields a nontrivial interaction which is conformal invariant. The exisitence of the nontrivial window implies ``cutoff insensitivity'' of the physics prediction in spite of the ultraviolet dominance of the dynamics. In the formal limit D -> 4, the nontrivial window coincides with the known condition of the nontriviality of the four-dimensional gauged NJL model, $9/(2N_c) < N_f - N_c < 9/2 N_c$.

hep-ph↗
arXiv2004

New mechanism for the top-bottom mass hierarchy

We propose a mechanism to generate hierarchy between masses of the top and bottom quarks without fine tuning of the Yukawa coupling constants in the context of the two Higgs doublet model (THDM). In the THDM with a discrete symmetry, there exists the vacuum where only the top quark receives the mass of the order of the electroweak symmetry breaking scale $v(\simeq 246 GeV)$, while the bottom quark remains massless. By introducing a small soft-breaking parameter $m_3^2$ of the discrete symmetry, the bottom quark perturbatively acquires a nonzero mass. We show a model in which the small $m_3^2 [\sim v^2/(4π)^2]$ is generated by the dynamics above the cutoff scale of the THDM. The ratio $\tanβ$ of the two vacuum expectation values is necessarily very large; i.e., $\tan β\sim m_t/m_b$. We also find a salient relation, $1/\tanβ\simeq m_3^2/m_H^2$, where $m_H$ is the mass of the extra CP-even Higgs boson. Our scenario yields some specific features that can be tested in future collider experiments.

hep-ph↗
arXiv2004

Topped MAC with extra dimensions?

We perform the most attractive channel (MAC) analysis in the top mode standard model with TeV-scale extra dimensions, where the standard model gauge bosons and the third generation of quarks and leptons are put in D(=6,8,10,...) dimensions. In such a model, bulk gauge couplings rapidly grow in the ultraviolet region. In order to make the scenario viable, only the attractive force of the top condensate should exceed the critical coupling, while other channels such as the bottom and tau condensates should not. We then find that the top condensate can be the MAC for D=8, whereas the tau condensation is favored for D=6. The analysis for D=10 strongly depends on the regularization scheme. We predict masses of the top (m_t) and the Higgs (m_H), m_t=172-175 GeV and m_H=176-188 GeV for D=8, based on the renormalization group for the top Yukawa and Higgs quartic couplings with the compositeness conditions at the scale where the bulk top condenses. The Higgs boson in such a characteristic mass range will be immediately discovered in H -> WW^(*)/ZZ^(*) once the LHC starts.

hep-ph↗
arXiv2003

Dynamical Electroweak Symmetry Breaking from Extra Dimensions

We study the dynamical electroweak symmetry breaking (DEWSB) in the $D (=6,8,...)$-dimensional bulk with compactified extra dimensions. We identify the critical binding strength for triggering the DEWSB, based on the ladder Schwinger-Dyson equation. In the top mode standard model with extra dimensions, where the standard model gauge bosons and the third generation of quarks and leptons are put in the bulk, we analyze the most attractive channel (MAC) by using renormalization group equations (RGEs) of (dimensionless) bulk gauge couplings and determine the effective cutoff where the MAC coupling exceeds the critical value. We then find that the top-condensation can take place for D=8. Combining RGEs of top-Yukawa and Higgs-quartic couplings with compositeness conditions, we predict the top mass, $m_t=173-180$ GeV, and the Higgs mass, $m_H=181-211$ GeV, for D=8, where we took the universal compactification scale $1/R = 1-100$ TeV.

hep-ph↗
arXiv2002

Calculating the pion decay constant from α_s(M_Z)

We revisit the analysis of the improved ladder Schwinger-Dyson (SD) equation for the dynamical chiral symmetry breaking in QCD with emphasizing the importance of the scale ambiguity. Previous calculation done so far naively used one-loop MSbar coupling in the improved ladder SD equation without examining the scale ambiguity. As a result, the calculated pion decay constant f_πwas less than a half of its experimental value f_π=92.4MeV once the QCD scale is fixed from the high energy coupling α_s(M_Z). In order to settle the ambiguity in a proper manner, we adopt here in the present paper the next-to-leading-order effective coupling instead of a naive use of the MSbar coupling. The pion decay constant f_πis then calculated from high energy QCD coupling strength α_s(M_Z)=0.1172 \pm 0.0020. Within the Higashijima-Miransky approximation, we obtain f_π=85--106MeV depending on the value of α_s(M_Z) which agrees well with the experimentally observed value f_π=92.4MeV. The validity of the improved ladder SD equation is therefore ascertained more firmly than considered before.

hep-ph↗