14 research outputs found
Chiral dynamics in a magnetic field from the functional renormalization group
We investigate the quark-meson model in a magnetic field using the exact
functional renormalization group equation beyond the local-potential
approximation. Our truncation of the effective action involves anisotropic wave
function renormalization for mesons, which allows us to investigate how the
magnetic field distorts the propagation of neutral mesons. Solving the flow
equation numerically, we find that the transverse velocity of mesons decreases
with the magnetic field at all temperatures, which is most prominent at zero
temperature. The meson screening masses and the pion decay constants are also
computed. The constituent quark mass is found to increase with magnetic field
at all temperatures, resulting in the crossover temperature that increases
monotonically with the magnetic field. This tendency is consistent with most
model calculations but not with the lattice simulation performed at the
physical point. Our work suggests that the strong anisotropy of meson
propagation may not be the fundamental origin of the inverse magnetic
catalysis.Comment: 37 pages, 10 figures. v2: References added, the version published in
JHE
Magnetic susceptibility of a strongly interacting thermal medium with 2+1 quark flavors
Thermodynamics of the three-flavor quark-meson model with axial anomaly is
studied in the presence of external magnetic fields. The nonperturbative
functional renormalization group is employed in order to incorporate quantum
and thermal fluctuations beyond the mean-field approximation. We calculate the
magnetic susceptibility with proper renormalization and find that the system is
diamagnetic in the hadron phase and paramagnetic in the hot plasma phase. The
obtained values of the magnetic susceptibility are in reasonable agreement with
the data from first-principle lattice QCD. Comparison with the mean-field
approximation, the Hadron Resonance Gas model and a free gas with
temperature-dependent masses is also made.Comment: 28 pages, 5 figure
Second-order and Fluctuation-induced First-order Phase Transitions with Functional Renormalization Group Equations
We investigate phase transitions in scalar field theories using the
functional renormalization group (RG) equation. We analyze a system with
U(2)xU(2) symmetry, in which there is a parameter that controls the
strength of the first-order phase transition driven by fluctuations. In the
limit of \lambda_2\to0\epsilon$-expansion results. We compare results from the expansion and from
the full numerical calculation and find that the fourth-order expansion is only
of qualitative use and that the sixth-order expansion improves the quantitative
agreement.Comment: 15 pages, 10 figures, major revision; discussions on O(N) models
reduced, a summary section added after Introduction, references added; to
appear in PR
Fluctuations in the quark-meson model for QCD with isospin chemical potential
We study the two-flavor quark-meson (QM) model with the functional
renormalization group (FRG) to describe the effects of collective mesonic
fluctuations on the phase diagram of QCD at finite baryon and isospin chemical
potentials, and . With only isospin chemical potential there is
a precise equivalence between the competing dynamics of chiral versus pion
condensation and that of collective mesonic and baryonic fluctuations in the
quark-meson-diquark model for two-color QCD at finite baryon chemical
potential. Here, finite introduces an additional dimension to the
phase diagram as compared to two-color QCD, however. At zero temperature, the
()-plane of this phase diagram is strongly constrained by the
"Silver Blaze problem." In particular, the onset of pion condensation must
occur at , independent of as long as
stays below the constituent quark mass of the QM model or the liquid-gas
transition line of nuclear matter in QCD. In order to maintain this relation
beyond mean field it is crucial to compute the pion mass from its timelike
correlator with the FRG in a consistent way.Comment: 10 pages, 11 figures; matches published versio
臨界ゆらぎを取り込んだQCDカイラル相転移の解析
京都大学0048新制・課程博士博士(理学)甲第17347号理博第3844号新制||理||1555(附属図書館)30113京都大学大学院理学研究科物理学・宇宙物理学専攻(主査)教授 大西 明, 教授 國廣 悌二, 教授 青山 秀明学位規則第4条第1項該当Doctor of ScienceKyoto UniversityDA
Real-time correlation functions in the O(N) model from the functional renormalization group
In the framework of the functional renormalization group (FRG) we present a
simple truncation scheme for the computation of real-time mesonic n-point
functions, consistent with the derivative expansion of the effective action.
Via analytic continuation on the level of the flow equations we perform
calculations of mesonic spectral functions in the scalar O(N) model, which we
use as an exploratory example. By investigating the renormalization-scale
dependence of the 2-point functions we shed light on the nature of the sigma
meson, whose spectral properties are predominantly of dynamical origin.Comment: 7 pages, 11 figures; published versio