Nuclear Theory·nucl-th

Tuesday·May 9, 2017

12 papers—9 primary·3 cross-listed

10
[Submitted on 1 May 2017] (cross-list from hep-lat)
Sign problem in $Z_{3}$ -symmetric effective Polyakov-line model
Takehiro Hirakida🇯🇵 · Junpei Sugano🇯🇵 · Hiroaki Kouno🇯🇵 · Junichi Takahashi🇯🇵 · Masanobu Yahiro🇯🇵
As an effective model corresponding to $Z_{3}$ -symmetric QCD ( $Z_{3}$ -QCD), we construct a $Z_{3}$ -symmetric effective Polyakov-line model ( $Z_{3}$ -EPLM) by using the logarithmic fermion effective action. Since $Z_{3}$ -QCD tends to QCD in the zero temperature limit, $Z_{3}$ -EPLM also agrees with the ordinary effective Polyakov-line model (EPLM) there; note that ordinary EPLM does not possess $Z_{3}$ symmetry. Our main purpose is to discuss a sign problem appearing in $Z_{3}$ -EPLM. The action of $Z_{3}$ -EPLM is real, when the Polyakov line is not only real but also its $Z_{3}$ images. This suggests that the sign problem becomes milder in $Z_{3}$ -EPLM than in EPLM. In order to confirm this suggestion, we do lattice simulations for both EPLM and $Z_{3}$ -EPLM by using the reweighting method with the phase quenched approximation. In the low-temperature region, the sign problem is milder in $Z_{3}$ -EPLM than in EPLM. We also propose a new reweighting method. This makes the sign problem very weak in $Z_{3}$ -EPLM.
Comments:
16 pages, 38 figures
Subjects:
High Energy Physics — Lattice (hep-lat)
arXiv:
1705.00665 [pdf]
PRD(2017)·14 citations
11
[Submitted on 8 May 2017] (cross-list from cond-mat.quant-gas)
Flow equations for cold Bose gases
A. G. Volosniev · H.-W. Hammer
We derive flow equations for cold atomic gases with one macroscopically populated energy level. The generator is chosen such that the ground state decouples from all other states in the system as the renormalization group flow progresses. We propose a self-consistent truncation scheme for the flow equations at the level of three-body operators and show how they can be used to calculate the ground state energy of a general $N$ -body system. Moreover, we provide a general method to estimate the truncation error in the calculated energies. Finally, we test our scheme by benchmarking to the exactly solvable Lieb-Liniger model and find good agreement for weak and moderate interaction strengths.
Subjects:
Quantum Gases (cond-mat.quant-gas); Nuclear Theory (nucl-th); Quantum Physics (quant-ph)
arXiv:
1705.02834 [pdf]
New J.Phys.(2017)·9 citations
12
[Submitted on 8 May 2017] (cross-list from hep-ph)
Thermalization of overpopulated systems in the 2PI formalism
Shoichiro Tsutsui🇯🇵 · Jean-Paul Blaizot🇯🇵 · Yoshitaka Hatta🇯🇵
Based on the two-particle irreducible (2PI) formalism to next-to-leading order in the $1/ N$ expansion, we study the thermalization of overpopulated systems in scalar $O (N)$ theories with moderate coupling. We focus in particular on the growth of soft modes, and examine whether this can lead to the formation of a transient Bose-Einstein condensate (BEC) when the initial occupancy is high enough. For the value of the coupling constant used in our simulations, we find that while the system rapidly approaches the condensation threshold, the formation of a BEC is eventually hindered by particle number changing processes.
Comments:
19 pages, 7 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Quantum Gases (cond-mat.quant-gas); Nuclear Theory (nucl-th)
arXiv:
1705.02872 [pdf]
PRD(2017)·13 citations

Affiliations

first authorsco-authorsvia INSPIRE

Sign problem in Z3​-symmetric effective Polyakov-line model

Flow equations for cold Bose gases

Thermalization of overpopulated systems in the 2PI formalism

Affiliations

Sign problem in $Z_{3}$ -symmetric effective Polyakov-line model