arXiv subjects

Chihiro Sasaki

Publications and source records attributed to Chihiro Sasaki.

At least 73 records · Page 4Linked to original sources

arXiv2016

Interplay between Deconfinement and Chiral Properties

We study interplay between confinement/deconfinement and chiral properties. We derive some analytical relations of the Dirac modes with the confinement quantities, such as the Polyakov loop, its susceptibility and the string tension. For the confinement quantities, the low-lying Dirac eigenmodes are found to give negligible contribution, while they are essential for chiral symmetry breaking. This indicates no direct, one-to-one correspondence between confinement/deconfinement and chiral properties in QCD. We also investigate the Polyakov loop in terms of the eigenmodes of the Wilson, the clover and the domain-wall fermion kernels, respectively.

hep-lat↗

arXiv2015

Dirac spectrum representation of Polyakov loop fluctuations in lattice QCD

Dirac spectrum representations of the Polyakov loop fluctuations are derived on the temporally odd-number lattice, where the temporal length is odd with the periodic boundary condition. We investigate the Polyakov loop fluctuations based on these analytical relations. It is semianalytically and numerically found that the low-lying Dirac eigenmodes have little contribution to the Polyakov loop fluctuations, which are sensitive probe for the quark deconfinement. Our results suggest no direct one-to-one corresponding between quark confinement and chiral symmetry breaking in QCD.

hep-lat↗

arXiv2015

Matching the Hagedorn mass spectrum with Lattice QCD results

Based on recent Lattice QCD (LQCD) results obtained at finite temperature, we discuss modeling of the hadronic phase of QCD in the framework of Hadron Resonance Gas (HRG) with discrete and continuous mass spectra. We focus on fluctuations of conserved charges, and show how a common limiting temperature can be used to constrain the Hagedorn exponential mass spectrum in different sectors of quantum number, through a matching of HRG and LQCD. For strange baryons, the extracted spectra are found to be consistent with all known and expected states listed by the Particle Data Group (PDG). The strange-mesonic sector, however, requires additional states in the intermediate mass range beyond that embodied in the database.

nucl-th↗

arXiv2015

Strangeness fluctuations from $K-π$ interactions

Motivated by recent lattice QCD studies, we explore the effects of interactions on strangeness fluctuations in strongly interacting matter at finite temperature. We focus on S-wave $Kπ$ scattering and discuss the role of the $K_0^*(800)$ and $K^*(1430)$ resonances. The interaction contribution is obtained within the S-matrix formulation of thermodynamics, using the empirical $Kπ$ phase shifts as input. We find that the simplified treatment of the interactions in this channel, employed in the hadron resonance gas approach, leads to an overestimate of the strangeness fluctuations. Thus, our calculation indicates that broad resonances must be treated with caution, when modeling QCD thermodynamics in the hadronic phase.

hep-ph↗

arXiv2015

Polyakov loop fluctuations in Dirac eigenmode expansion

We investigate correlations of the Polyakov loop fluctuations with eigenmodes of the lattice Dirac operator. Their analytic relations are derived on the temporally odd-number size lattice with the normal non-twisted periodic boundary condition for the link-variables. We find that the low-lying Dirac modes yield negligible contributions to the Polyakov loop fluctuations. This property is confirmed to be valid in confined and deconfined phase by numerical simulations in SU(3) quenched QCD. These results indicate that there is no direct, one-to-one correspondence between confinement and chiral symmetry breaking in QCD in the context of different properties of the Polyakov loop fluctuation ratios.

hep-lat↗

arXiv2015

An effective model for the QCD phase transitions at finite baryon density

We introduce an effective quark-meson-nucleon model for the QCD phase transitions at finite baryon density. The nucleon and the quark degrees of freedom are described within a unified framework of a chiral linear sigma model. The deconfinement transition is modeled through a simple modification of the distribution functions of nucleons and quarks, where an additional auxiliary field, the bag field, is introduced. The bag field plays a key role in converting between the nucleon and the quark degrees of freedom. The model predicts that the chiral and the deconfinement phase transitions are always separated. Depending on the model parameters, the chiral transition occurs in the baryon density range of $(1.5-15.5)n_0$, while the deconfinement transition occurs above $5 n_0$, where $n_0$ is the saturation density.

hep-ph↗

arXiv2015

Correlations between light and heavy flavors near the chiral crossover

Thermal fluctuations and correlations between the light and heavy-light mesons are explored within a chiral effective theory implementing heavy quark symmetry. We show, that various heavy-light flavor correlations indicate a remnant of the chiral criticality in a narrow range of temperature where the chiral susceptibility exhibits a peak structure. The onset of the chiral crossover, in the heavy-light flavor correlations, is therefore independent from the light flavors. This indicates that the fluctuations carried by strange charmed mesons can also be used to identify the chiral crossover, which is dominated by the non-strange light quark dynamics.

hep-ph↗

arXiv2015

Chiral Thermodynamics with Charm

Chiral thermodynamics of charmed mesons is formulated at finite temperature within a $2+1+1$-flavored effective Lagrangian incorporating heavy quark symmetry. The chiral mass splittings are shown to be less sensitive to the light-quark flavors, attributed to the underlying heavy quark symmetry. Consequently, chiral symmetry restoration is more accelerated in the strange charmed-mesons than in the strange light mesons, and this is in striking contrast to the chiral SU(4) result. We also show the correlations between light and heavy flavors around the chiral crossover.

hep-ph↗

arXiv2014

Fate of charmed mesons near chiral symmetry restoration in hot matter

Chiral thermodynamics of charmed mesons is formulated at finite temperature within a $2+1+1$-flavored effective Lagrangian incorporating heavy quark symmetry. The charmed-meson mean fields act as an extra source which breaks the chiral symmetry explicitly. This leads to effective interactions between the light and heavy-light mesons, which intrinsically depend on temperature. Effective masses of the scalar and pseudoscalar charmed-mesons tend to approach each other as increasing temperature, so that the splitting between the chiral partners is reduced. These chiral splittings are shown to be less sensitive to the light-quark flavors, attributed to the underlying heavy quark symmetry. Consequently, chiral symmetry restoration is more manifest for the strange charmed-mesons than for the strange light mesons. The effective masses are also compared with the results in the one-loop chiral perturbation theory. A substantial difference is found at a relatively low temperature, $T \sim f_π$.

hep-ph↗

arXiv2014

Selected Issues in Thermal Field Theory

New developments on hot and dense QCD in effective field theories are reviewed. Recent investigations in lattice gauge theories for the low-lying Dirac eigenmodes suggest survival hadrons in restored phase of chiral symmetry. We discuss expected properties of those bound states in a medium using chiral approaches. The role of higher-lying hadrons near chiral symmetry restoration is also argued from the conventional and the holographic point of view.

hep-ph↗

arXiv2013

Interplay between chromoelectric and chromomagnetic gluons in Yang-Mills thermodynamics

We propose an effective theory of SU(3) gluonic matter where interactions between color-electric and color-magnetic gluons are constrained by the center and scale symmetries. Through matching to the dimensionally-reduced magnetic theories, the magnetic gluon condensate qualitatively changes its thermal behavior above the critical temperature. We argue its phenomenological consequences for the thermodynamics, in particular the dynamical breaking of scale invariance.

hep-ph↗

arXiv2013

Yang-Mills Thermodynamics: an Effective Theory Approach

We derive the Polyakov-loop thermodynamic potential in the perturbative approach to pure SU(3) Yang-Mills theory. The potential expressed in terms of the Polyakov loop in the fundamental representation corresponds to that of the strong-coupling expansion, of which the relevant coefficients of the gluon energy distribution are specified by characters of the SU(3) group. At high temperatures the derived gluon potential exhibits the correct asymptotic behavior, whereas at low temperatures, it disfavors gluons as appropriate dynamical degrees of freedom. In order to quantify the Yang-Mills thermodynamics in a confined phase, we propose a hybrid approach which matches the effective gluon potential to the one of glueballs constrained by the QCD trace anomaly in terms of a dilaton. We also discuss the interplay between the chromomagnetic and chromoelectric gluon dynamics.

hep-ph↗

arXiv2013

Implementation of chromomagnetic gluons in Yang-Mills thermodynamics

Motivated by the recent high-precision lattice data on Yang-Mills equations of state, we propose an effective theory of SU(3) gluonic matter. The theory is constructed based on the center and scale symmetries and their dynamical breaking, so that the interplay between color-electric and color-magnetic gluons is included coherently. We suggest, that the magnetic gluon condensate changes its thermal behavior qualitatively above the critical temperature, as a consequence of the matching to dimensionally-reduced magnetic theories. We consider thermodynamics in the mean field approximation and discuss the properties and interpretation of the trace anomaly.

hep-ph↗

arXiv2013

Interplay between ω-Nucleon Interaction and Nucleon Mass in Dense Baryonic Matter

The dilaton-limit fixed point and the scaling properties of hadrons in the close vicinity of the fixed point in dense baryonic matter uncovered in hidden local symmetry implemented with spontaneously broken scale symmetry are shown to reveal a surprisingly intricate interplay, hitherto unsuspected, between the origin of the bulk of proton mass and the renormalization-group flow of the ω-nuclear interactions. This rends a theoretical support to the previous (phenomenologically) observed correlation between the dropping nucleon mass and the behavior of the ω-nuclear interactions in dense matter described in terms of half skyrmions that appear at a density denoted $n_{1/2}$ in skyrmion crystals. The role of the ω-meson degree of freedom in the source for nucleon mass observed in this paper is highly reminiscent of its important role in the skyrmion description of nucleon mass in hidden local symmetric theory. One of the most notable novel results found in this paper is that the nucleon mass in dense baryonic medium undergoes a drop roughly linear in density up to a density (denoted $\tilde{n}$) slightly above nuclear matter density ($n_0$) and then stays more or less constant up to the dilaton limit fixed point. The possibility that we entertain is that $\tilde{n}$ coincides with or at least close to $n_{1/2}$. We note that this feature can be economically captured by the parity-doublet model for nucleons with the chiral-invariant mass $m_0\sim (0.7-0.8) m_N$. It is found in one-loop renormalization-group analysis with the Lagrangian adopted that while the ρ-NN coupling "runs" in density, the ω-NN coupling does not scale: it will scale at two-loop or higher-loop order, but at a slower pace, so it is more appropriate to say it "walks" rather than runs.

nucl-th↗

arXiv2013

Polyakov loop fluctuations in SU(3) lattice gauge theory and an effective gluon potential

We calculate the Polyakov loop susceptibilities in the SU(3) lattice gauge theory using the Symanzik improved gauge action on different-sized lattices. The longitudinal and transverse fluctu- ations of the Polyakov loop, as well as, that of its absolute value are considered. We analyze their properties in relation to the confinement-deconfinement phase transition. We also present results based on simulations of (2+1)-flavor QCD on 32^3 x 8 lattice using Highly Improved Staggered Quark (HISQ) action by the HotQCD collaboration. The influences of fermions on the Polyakov loop fluctuations are discussed. We show, that ratios of different susceptibilities of the Polyakov loop are sensitive probes for critical behavior. We formulate an effective model for the Polyakov loop potential and constrain its parameters from existing quenched lattice data including fluctuations. We emphasize the role of fluctuations to fully explore the thermodynamics of pure gauge theory within an effective approach.

hep-lat↗

arXiv2013

Probing Deconfinement with Polyakov Loop Susceptibilities

The susceptibilities of the real and imaginary parts, as well as of the modulus of the Polyakov loop, are computed in SU(3) lattice gauge theory. We show that the ratios of these susceptibilities are excellent probes of the deconfinement transition, independent of the renormalization of the Polyakov loop and only weakly dependent on the system size. The ratios are almost temperature independent above and below the transition and exhibit a discontinuity at the transition temperature. This characteristic behavior can be understood in terms of the global Z(3) symmetry of the Yang-Mills Lagrangian and the general properties of the Polyakov loop probability distribution.

hep-lat↗

arXiv2013

The phase diagram of nuclear and quark matter at high baryon density

We review theoretical approaches to explore the phase diagram of nuclear and quark matter at high baryon density. We first look over the basic properties of quantum chromodynamics (QCD) and address how to describe various states of QCD matter. In our discussions on nuclear matter we cover the relativistic mean-field model, the chiral perturbation theory, and the approximation based on the large-Nc limit where Nc is the number of colors. We then explain the liquid-gas phase transition and the inhomogeneous meson condensation in nuclear matter with emphasis put on the relevance to quark matter. We commence the next part focused on quark matter with the bootstrap model and the Hagedorn temperature. Then we turn to properties associated with chiral symmetry and exposit theoretical descriptions of the chiral phase transition. There emerge some quark-matter counterparts of phenomena seen in nuclear matter such as the liquid-gas phase transition and the inhomogeneous structure of the chiral condensate. The third regime that is being recognized recently is what is called quarkyonic matter, which has both aspects of nuclear and quark matter. We closely elucidate the basic idea of quarkyonic matter in the large-Nc limit and its physics implications. Finally, we discuss some experimental indications for the QCD phase diagram and close the review with outlooks.

hep-ph↗

arXiv2013

Effective gluon potential and Yang-Mills thermodynamics

We derive the Polyakov-loop thermodynamic potential in the perturbative approach to pure SU(3) Yang-Mills theory. The potential expressed in terms of the Polyakov loop in the fundamental representation corresponds to that of the strong-coupling expansion, of which the relevant coefficients of the gluon energy distribution are specified by characters of the SU(3) group. At high temperature, the potential exhibits the correct asymptotic behavior, whereas at low temperature, it disfavors gluons as appropriate dynamical degrees of freedom. To quantify the Yang-Mills thermodynamics in confined phase, we introduce a hybrid approach which matches the effective gluon potential to that of glueballs, constrained by the QCD trace anomaly in terms of dilaton fields.

hep-ph↗