Searcharxiv⌕ Search

arXiv subjects

Chihiro Sasaki

Publications and source records attributed to Chihiro Sasaki.

At least 91 records · Page 5Linked to original sources
arXiv2012

An effective gluon potential and hybrid approach to Yang-Mills thermodynamics

We derive the partition function for the SU(3) Yang-Mills theory in the presence of a uniform gluon field within the background field method. We show, that the $n$-body gluon contributions in the partition function are characterized solely by the Polyakov loop. We express the effective action through characters of different representations of the color gauge group resulting in a form deduced in the strong-coupling expansion. A striking feature of this potential is that at low temperature gluons are physically disfavored and therefore they do not yield the correct thermodynamics. We suggest a hybrid approach to Yang-Mills thermodynamics, combining the effective gluon potential with glueballs implemented as dilaton fields.

hep-ph↗
arXiv2012

Dilaton-Limit Fixed Point in Hidden Local Symmetric Parity Doublet Model

We study nucleon structure with positive and negative parities using a parity doublet model endowed with hidden local symmetry (HLS) with the objective to probe dense baryonic matter. The model -- that we shall refer to as "PDHLS model" for short -- allows a chiral-invariant mass of the nucleons unconnected to spontaneously broken chiral symmetry which comes out to be m_0 ~ 200 MeV at tree level from fitting to the decay width of the parity doubler, N(1535), to nucleon-pion and nucleon axial coupling g_A=1.267. The presence of a substantial m_0 that remains non-vanishing at chiral restoration presents a deep issue for the origin of the nucleon mass as well as will affect nontrivially the equation of state for dense baryonic matter relevant for compact stars. We construct a chiral perturbation theory at one-loop order and explore the phase structure of the model using renormalization group equations. We find a fixed point that corresponds exactly to the "dilaton limit" at which the HLS vector mesons decouple from the nucleons before reaching the vector manifestation fixed point. We suggest that cold baryonic system will flow to this limit as density increases toward that of chiral restoration.

hep-ph↗
arXiv2012

Suppression of the repulsive force in nuclear interactions near the chiral phase transition

We introduce an effective chiral Lagrangian with a dilaton responsible for the trace anomaly in QCD. As the "dilaton limit" is taken, which drives a system to near chiral restoration density, a linear sigma model emerges from the highly non-linear structure. A striking prediction is that the vector-meson--nucleon interaction gets strongly suppressed when the dilaton limit is approached. Its phenomenological implications for the thermodynamics of dense baryonic matter are briefly discussed.

hep-ph↗
arXiv2011

The phase structure of a chiral model with dilatons in hot and dense matter

We explore the phase structure of a chiral model of constituent quarks and gluons implementing scale symmetry breaking at finite temperature and chemical potential. In this model the chiral dynamics is intimately linked to the trace anomaly saturated by a dilaton field. The thermodynamics is governed by two condensates, thermal expectation values of sigma and dilaton fields, which are the order parameters responsible for the phase transitions associated with the chiral and scale symmetries. Within the mean field approximation, we find that increasing temperature a system experiences a chiral phase transition and then a first-order phase transition of partial scale symmetry restoration characterized by a melting gluon-condensate takes place at a higher temperature. There exists a region at finite chemical potential where the scale symmetry remains dynamically broken while the chiral symmetry is restored. We also give a brief discussion on the sigma-meson mass constrained from Lattice QCD.

hep-ph↗
arXiv2011

Chiral Symmetry Breaking, Trace Anomaly and Baryons in Hot and Dense Matter

We propose an effective chiral Lagrangian with a chiral scalar introduced as a dilaton associated with broken conformal symmetry and responsible for the trace anomaly in QCD and discuss the properties of hadronic matter at high density and temperature. As the "dilaton limit" is taken, which drives a system from nuclear matter density to near chiral restoration density, a linear sigma model emerges from the highly non-linear structure. A striking prediction is that as the dilaton limit is approached, the omega-nucleon interaction gets strongly suppressed at high density. This is shown to be a firm statement at the quantum level protected by an infrared fixed point of the renormalization group equations derived in chiral perturbation theory.

hep-ph↗
arXiv2011

Conformal anomaly and the vector coupling in dense matter

We construct an effective chiral Lagrangian for hadrons implemented by the conformal invariance and discuss the properties of nuclear matter at high density. The model is formulated based on two alternative assignment, "naive" and mirror, of chirality to the nucleons. It is shown that taking the dilaton limit, in which the mended symmetry of Weinberg is manifest, the vector-meson Yukawa coupling becomes suppressed and the symmetry energy becomes softer as one approaches the chiral phase transition. This leads to softer equations of state (EoS) and could accommodate the EoS without any exotica consistent with the recent measurement of a $1.97 \pm 0.04\,M_\odot$ neutron star.

hep-ph↗
arXiv2010

Chiral thermodynamics of dense hadronic matter

We discuss phases of hot and dense hadronic matter using chiral Lagrangians. A two-flavored parity doublet model constrained by the nuclear matter ground state predicts chiral symmetry restoration. The model thermodynamics is shown within the mean field approximation. A field-theoretical constraint on possible phases from the anomaly matching is also discussed.

hep-ph↗
arXiv2010

Chiral Thermodynamics of Dense QCD

We show a phase diagram of a two-flavored parity doublet model on top of the nuclear matter ground state within the mean field approximation. An exotic phase with unbroken center symmetry of chiral group is also discussed. When crossing this phase boundary the baryon number susceptibility exhibits a characteristic feature.

hep-ph↗
arXiv2010

Vector mesons at finite temperature and QCD sum rules

Finite energy sum rules for vector and axial-vector currents are derived in a thermal medium to provide constraints for the spectral behavior of rho and a1 mesons at nonvanishing temperature and hence to study the tendency toward chiral symmetry restoration. The parity-mixing ansatz for the rho and a1 spectra, including finite widths, is investigated as a function of temperature. Characteristic differences between vector and axial-vector channels are discussed with regard to the implementation of the chiral-symmetry-breaking scale, 4pi times the pion decay constant, in the sum rule approach.

nucl-th↗
arXiv2010

Thermodynamics of dense hadronic matter in a parity doublet model

We study thermodynamics of nuclear matter in a two-flavored parity doublet model within the mean field approximation. Parameters of the model are chosen to reproduce correctly the properties of the nuclear ground state. The model predicts two phase transitions in nuclear matter, a liquid-gas phase transition at normal nuclear density and a chiral transition at higher density. At finite temperature the pion decay constant exhibits a considerable reduction at intermediate values of chemical potential, which is traced back to the presence of the liquid-gas transition, and approaches zero at higher chemical potential associated with the chiral symmetry restoration. A "transition" from meson-rich to baryon-rich matter is also discussed.

hep-ph↗
arXiv2010

Thermodynamics of dense matter in chiral approaches

We discuss phases in dense hadronic and quark matter from chiral model approaches. Within PNJL models the phase diagram for various number of colors $N_c$ is studied. How phases are constrained in quantum field theories are also discussed along with the anomaly matching. An exotic phase with unbroken center symmetry of chiral group has a characteristic feature in the thermodynamics, which can be interpreted as one realization of the quarkyonic phase in QCD for $N_c=3$.

hep-ph↗
arXiv2010

Effect of vector--axial-vector mixing to dilepton spectrum

In this write-up we summarize main results of our recent analyses on the mixing between transverse rho and a1 mesons in hot and/or dense matter. We show that the axial-vector meson contributes significantly to the vector spectral function in hot matter through the mixing. In dense baryonic matter, we include a mixing through a set of omega rho a1 -type interactions. We show that a clear enhancement of the vector spectral function appears below \sqrt{s}=m_ρfor small three-momenta of the rho meson, and thus the vector spectrum exhibits broadening.

hep-ph↗
arXiv2009

The Phase Structure of Dense QCD from Chiral Models

A new phase of dense QCD proposed in the limit of large number of colors, Quarkyonic Phase, is discussed in chiral approaches. The interplay between chiral symmetry breaking and confinement together with the $N_c$ dependence of the phase diagram are dealt with in the PNJL model. We also discuss a possible phase at finite density where chiral symmetry is spontaneously broken while its center remains unbroken. The quark number susceptibility exhibits a strong enhancement at the restoration point of the center symmetry rather than that of the chiral symmetry. This is reminiscent of the quarkyonic transition.

hep-ph↗
arXiv2009

The QCD Phase Diagram from Chiral Approaches

I show an updated QCD phase diagram with recent developments from chiral effective theories and phenomenological models. Expected signals of a QCD critical point accessible in heavy-ion collisions are also discussed. In particular, non-monotonic behavior of fluctuations associated with conserved charges is focused on.

hep-ph↗
arXiv2009

A novel spectral broadening from vector--axial-vector mixing in dense matter

The presence of baryonic matter leads to the mixing between transverse $ρ$ and $a_1$ mesons through a set of $ωρa_1$-type interactions, which results in the modification to the dispersion relation. We show that a clear enhancement of the vector spectral function appears below $\sqrt{s}=m_ρ$ for small three-momenta of the $ρ$ meson, and thus the vector spectrum exhibits broadening. We also discuss its relevance to dilepton measurements.

hep-ph↗
arXiv2009

Hidden Local Field Theory and Dileptons in Relativistic Heavy Ion Collisions

The notion of "hadronic freedom" is introduced based on the vector manifestation of hidden local symmetry and is used to suggest that the dileptons measured in relativistic heavy-ion collisions do not provide {\em direct} information on the spontaneous breaking of chiral symmetry and hence on the mechanism for mass generation of light-quark hadrons. We give arguments how the dileptons emitted from those vector mesons whose masses are shifted à la Brown-Rho (BR) scaling by the vacuum change in temperature -- as in heavy-ion collisions -- and/or density -- as in cold compressed matter -- could be strongly suppressed in the hadronic free region between the chiral restoration point and the "flash point" at which the vector mesons recover $\gsim 90%$ of their free-space on-shell masses and the full strong coupling strength. It may seem ironical that the very mechanism i.e., the vector manifestation in hidden local symmetry, that is to make the mass drop and modify the spectral function is in turn responsible for the dilepton suppression. A possible falsification of this drastic prediction will be indicated. We also briefly discuss the potential role played by the holographic dimension intrinsic in gravity-gauge duality that provides a unified field theory description of hadrons -- both mesons and baryons -- under extreme conditions. Baryons arise as coherent states of pions and vector mesons of holographic QCD which define the ground state or the "vacuum" on which mesonic excitations could undergo BR scaling.

hep-ph↗
arXiv2008

Dilepton Production from Dropping rho in the Vector Manifestation

In this write-up we summarize the main result of our analysis on the thermal dilepton production rate from the dropping rho based on the vector manifestation (VM). In the analysis, we showed that the effect of the strong violation of the vector dominance (VD) predicted by the VM, substantially suppresses the dilepton production rate compared with the one predicted by assuming the VD together with the dropping rho.

hep-ph↗