Nuclear Theory·nucl-th

Tuesday·December 5, 2017

17 papers—8 primary·9 cross-listed

09
Chiral magnetic effect search in p+Au, d+Au and Au+Au collisions at RHIC
Jie Zhao (for the STAR collaboration)🇺🇸
Metastable domains of fluctuating topological charges can change the chirality of quarks and induce local parity violation in quantum chromodynamics. This can lead to observable charge separation along the direction of the strong magnetic field produced by spectator protons in relativistic heavy-ion collisions, a phenomenon called the chiral magnetic effect (CME). A major background source for CME measurements using the charge-dependent azimuthal correlator ( $Δ γ$ ) is the intrinsic particle correlations (such as resonance decays) coupled with the azimuthal elliptical anisotropy ( $v_{2}$ ). In heavy-ion collisions, the magnetic field direction and event plane angle are correlated, thus the CME and the $v_{2}$ -induced background are entangled. In this report, we present two studies from STAR to shed further lights on the background issue. (1) The $Δ γ$ should be all background in small system p+Au and d+Au collisions, because the event plane angles are dominated by geometry fluctuations uncorrelated to the magnetic field direction. However, significant $Δ γ$ is observed, comparable to the peripheral Au+Au data, suggesting a background dominance in the latter, and likely also in the mid-central Au+Au collisions where the multiplicity and $v_{2}$ scaled correlator is similar. (2) A new approach is devised to study $Δ γ$ as a function of the particle pair invariant mass ( $m_{in v}$ ) to identify the resonance backgrounds and hence to extract the possible CME signal. Signal is consistent with zero within uncertainties at high $m_{in v}$ . Signal at low $m_{in v}$ , extracted from a two-component model assuming smooth mass dependence, is consistent with zero within uncertainties.
↳ hep-exnucl-exnucl-thEPJ Web Conf.(2018)·9 citations
10
Implications from GW170817 and I-Love-Q relations for relativistic hybrid stars
Vasileios Paschalidis🇺🇸 · Kent Yagi🇺🇸 · David Alvarez-Castillo🇩🇪 · David B. Blaschke🇷🇺 · Armen Sedrakian🇩🇪
Gravitational wave observations of GW170817 placed bounds on the tidal deformabilities of compact stars allowing one to probe equations of state for matter at supranuclear densities. Here we design new parametrizations for hybrid hadron-quark equations of state, that give rise to low-mass twin stars, and test them against GW170817. We find that GW170817 is consistent with the coalescence of a binary hybrid star--neutron star. We also test and find that the I-Love-Q relations for hybrid stars in the third family agree with those for purely hadronic and quark stars within $\sim 3%$ for both slowly and rapidly rotating configurations, implying that these relations can be used to perform equation-of-state independent tests of general relativity and to break degeneracies in gravitational waveforms for hybrid stars in the third family as well.
↳ astro-ph.HEgr-qchep-phnucl-thPRD(2018)·256 citations
11
Meson properties in magnetized quark matter
Ziyue Wang🇨🇳 · Pengfei Zhuang🇨🇳
We study neutral and charged meson properties in magnetic field. Taking bosolization method in a two-flavor Nambu--Jona-Lasinio model, we derive effective meson Lagrangian density with minimal coupling to the magnetic field, by employing derivative expansion for both the meson fields and Schwinger phases. We extract from the effective Lagrangian density the meson curvature, pole and screening masses. As the only Goldstone mode, the neutral pion controls the thermodynamics of the system and propagates the lang range quark interaction. The magnetic field breaks down the space symmetry, and the quark interaction region changes from a sphere in vacuum to a ellipsoid in magnetic field.
↳ hep-phnucl-thPRD(2018)·66 citations
12
Cooling of hypernuclear compact stars
Adriana R. Raduta (IFIN-HH)🇷🇴 · Armen Sedrakian (FIAS)🇩🇪 · Fridolin Weber (SDSU)🇺🇸
We study the thermal evolution of hypernuclear compact stars constructed from covariant density functional theory of hypernuclear matter and parameterizations which produce sequences of stars containing two-solar-mass objects. For the input in the simulations, we solve the Bardeen-Cooper-Schrieffer gap equations in the hyperonic sector and obtain the gaps in the spectra of $Λ$ , $Ξ^{0}$ and $Ξ^{-}$ hyperons. For the models with masses $M / M_{⊙} \geq 1.5$ the neutrino cooling is dominated by hyperonic direct Urca processes in general. In the low-mass stars the $(Λ p)$ plus leptons channel is the dominant direct Urca process, whereas for more massive stars the purely hyperonic channels $(Σ^{-} Λ)$ and $(Ξ^{-} Λ)$ are dominant. Hyperonic pairing strongly suppresses the processes on $Ξ^{-}$ s and to a lesser degree on $Λ$ s. We find that intermediate-mass $1.5 \leq M / M_{⊙} \leq 1.8$ models have surface temperatures which lie within the range inferred from thermally emitting neutron stars, if the hyperonic pairing is taken into account. Most massive models with $M / M_{⊙} ≃ 2$ may cool very fast via the direct Urca process through the $(Λ p)$ channel because they develop inner cores where the $S$ -wave pairing of $Λ$ s and proton is absent.
↳ astro-ph.HEastro-ph.SRnucl-thMNRAS(2018)·63 citations
13
Development of heavy-flavour flow-harmonics in high-energy nuclear collisions
Andrea Beraudo🇮🇹 · Arturo De Pace🇮🇹 · Marco Monteno🇮🇹 · Marzia Nardi🇮🇹 · Francesco Prino🇮🇹
We employ the POWLANG transport setup, developed over the last few years, to provide new predictions for several heavy-flavour observables in relativistic heavy-ion collisions from RHIC to LHC center-of-mass energies. In particular, we focus on the development of the flow-harmonics $v_{2}$ and $v_{3}$ arising from the initial geometric asymmetry in the initial conditions and its associated event-by-event fluctuations. Within the same transport framework, for the sake of consistency, we also compare the nuclear modification factor of the $p_{T}$ spectra of charm and beauty quarks, heavy hadrons and their decay electrons. We compare our findings to the most recent data from the experimental collaborations. We also study in detail the contribution to the flow harmonics from the quarks decoupling from the fireball during the various stages of its evolution: although not directly accessible to the experiments, this information can shed light on the major sources of the final measured effect.
↳ hep-phnucl-thJHEP(2018)·41 citations
14
Hadronic Lorentz Violation in Chiral Perturbation Theory Including the Coupling to External Fields
Rasha Kamand🇺🇸 · Brett Altschul🇺🇸 · Matthias R. Schindler🇺🇸
If any violation of Lorentz symmetry exists in the hadron sector, its ultimate origins must lie at the quark level. We continue the analysis of how the theories at these two levels are connected, using chiral perturbation theory. Considering a two-flavor quark theory, with dimension-4 operators that break Lorentz symmetry, we derive a low-energy theory of pions and nucleons that is invariant under local chiral transformations and includes the coupling to external fields. The pure meson and baryon sectors, as well as the couplings between them and the couplings to external electromagnetic and weak gauge fields, contain forms of Lorentz violation which depend on linear combinations of quark-level coefficients. In particular, at leading order the electromagnetic couplings depend on the very same combinations as appear in the free particle propagators. This means that observations of electromagnetic processes involving hadrons--such as vacuum Cerenkov radiation, which may be allowed in Lorentz-violating theories--can only reliably constrain certain particular combinations of quark coefficients.
↳ hep-phhep-thnucl-thPRD(2018)·14 citations
15
Secular Terms in Dyson Series to All-Orders of Perturbation
Satoshi Iso🇯🇵 · Hikaru Ohta🇯🇵 · Takao Suyama🇯🇵
In classical and quantum systems, perturbation of an evolution equation is often invalidated by secular terms which diverge at late times. The diverging behavior of evolution can be remedied by various techniques of resumma- tion such as renormalization group or multi-scale analysis. In this paper, we prove that, in a generic quantum mechanical system, secular terms can be systematically removed to all orders in the Dyson series by the method of improved (renormalized) perturbation. A recurrence relation to provide an explicit method to remove the secular terms is given. As a byproduct, we give a simple method to obtain energy eigenvalues and decay rates to all orders of perturbation.
↳ hep-thhep-phmath-phmath.MP+1PTEP(2018)·2 citations
16
Path optimization method for the sign problem
Akira Ohnishi🇯🇵 · Yuto Mori🇯🇵 · Kouji Kashiwa🇯🇵
We propose a path optimization method (POM) to evade the sign problem in the Monte-Carlo calculations for complex actions. Among many approaches to the sign problem, the Lefschetz-thimble path-integral method and the complex Langevin method are promising and extensively discussed. In these methods, real field variables are complexified and the integration manifold is determined by the flow equations or stochastically sampled. When we have singular points of the action or multiple critical points near the original integral surface, however, we have a risk to encounter the residual and global sign problems or the singular drift term problem. One of the ways to avoid the singular points is to optimize the integration path which is designed not to hit the singular points of the Boltzmann weight. By specifying the one-dimensional integration-path as $z = t + i f (t) (f \in R)$ and by optimizing $f (t)$ to enhance the average phase factor, we demonstrate that we can avoid the sign problem in a one-variable toy model for which the complex Langevin method is found to fail. In this proceedings, we propose POM and discuss how we can avoid the sign problem in a toy model. We also discuss the possibility to utilize the neural network to optimize the path.
↳ hep-lathep-phnucl-thEPJ Web Conf.(2018)·10 citations
17
IR properties of chiral effects in pionic matter
A. Avdoshkin🇷🇺 · A. V. Sadofyev🇷🇺 · V. I. Zakharov🇷🇺
Chiral effects exhibit peculiar universality in idealized theoretical limits. However, they are known to be infrared sensitive and get modified in more realistic settings. In this work, we study how the corresponding conductivities vary with the constituent mass. We concentrate on a pionic realization of chiral effects which provides a better control over infrared properties of the theory. The pionic medium is considered at finite vector and axial isospin chemical potentials in the presence of an external magnetic field. This system supports electric and axial isospin currents along the magnetic field which correspond to chiral magnetic and chiral separation effects. We show that these currents are sensitive to the finite mass of the constituents, but the conductivities follow a simple scaling with the corresponding charge densities as one would expect for polarization effects. It is argued that this relation can capture the dependence of chiral effects on other infrared parameters. Finally, we briefly comment on the realization of the 't Hooft matching condition in pionic media at finite densities.
↳ hep-phnucl-thPRD(2018)·12 citations

Affiliations

first authorsco-authorsvia INSPIRE