Nuclear Theory·nucl-th

Tuesday·September 26, 2017

15 papers—5 primary·10 cross-listed

06
Evidence for a maximum mass cut-off in the neutron star mass distribution and constraints on the equation of state
Justin Alsing🇺🇸 · Hector O. Silva🇺🇸 · Emanuele Berti🇺🇸
We infer the mass distribution of neutron stars in binary systems using a flexible Gaussian mixture model and use Bayesian model selection to explore evidence for multi-modality and a sharp cut-off in the mass distribution. We find overwhelming evidence for a bimodal distribution, in agreement with previous literature, and report for the first time positive evidence for a sharp cut-off at a maximum neutron star mass. We measure the maximum mass to be $2.0 M_{⊙} < m_{max} < 2.2 M_{⊙}$ (68\%), $2.0 M_{⊙} < m_{max} < 2.6 M_{⊙}$ (90\%), and evidence for a cut-off is robust against the choice of model for the mass distribution and to removing the most extreme (highest mass) neutron stars from the dataset. If this sharp cut-off is interpreted as the maximum stable neutron star mass allowed by the equation of state of dense matter, our measurement puts constraints on the equation of state. For a set of realistic equations of state that support $> 2 M_{⊙}$ neutron stars, our inference of $m_{max}$ is able to distinguish between models at odds ratios of up to $12 : 1$ , whilst under a flexible piecewise polytropic equation of state model our maximum mass measurement improves constraints on the pressure at $3 - 7 \times$ the nuclear saturation density by $\sim 30 - 50%$ compared to simply requiring $m_{max} > 2 M_{⊙}$ . We obtain a lower bound on the maximum sound speed attained inside the neutron star of $c_{s}^{max} > 0.63 c$ (99.8\%), ruling out $c_{s}^{max} < c / 3$ at high significance. Our constraints on the maximum neutron star mass strengthen the case for neutron star-neutron star mergers as the primary source of short gamma-ray bursts.
↳ astro-ph.HEgr-qcnucl-thMNRAS(2018)·278 citations
07
Thermal vorticity production in relativistic dissipative fluids
Yang-guang Yang🇨🇳 · Shi Pu🇯🇵
We have computed the circulation integrations of thermal vorticity with and without charged currents in dissipative fluids. We find that the relativistic Kelvin circulation theorem will be modified by the dissipative effects, therefore, the circulation integrations of thermal vorticity may not be conserved during the fluid evolution.
↳ hep-phnucl-thActa Phys.Polon.Supp.(2017)·2 citations
08
Regge phenomenology of photoproduction of $π^{-} Δ^{++}$ and scaling with saturation of trajectory
Byung-Geel Yu🇰🇷 · Kook-Jin Kong🇰🇷
In this work we investigate the reaction $γ p \to π^{-} Δ^{++}$ in the Reggeized model for $π (138) + ρ (775) + a_{2} (1320)$ exchanges in the $t$ -channel. For a convergence of the reaction cross section at high energies the minimal forms of proton and $Δ^{++}$ exchanges are introduced in the direct and crossed channels for gauge invariance of $π$ Regge-pole exchange. The role of spin-2 tensor meson $a_{2}$ is found to be crucial to agree with existing data at high energies. Electromagnetic multipoles of $Δ^{++}$ baryon are analyzed in the $Δ$ resonance region. Based on the constituents counting rule the scaled differential cross section at $E_{γ} = 4$ GeV is reproduced with the Regge trajectory saturated at large momentum transfer $- t$ .
↳ hep-phnucl-thPhys.Part.Nucl.Lett.(2018)·2 citations
09
Characteristics of Chiral Anomaly in View of Various Applications
Kazuo Fujikawa🇯🇵
In view of the recent applications of chiral anomaly to various fields beyond particle physics, we discuss some basic aspects of chiral anomaly which may help deepen our understanding of chiral anomaly in particle physics also. It is first shown that Berry's phase (and its generalization) for the Weyl model $H = v_{F} σ \cdot p (t)$ assumes a monopole form at the exact adiabatic limit but deviates from it off the adiabatic limit and vanishes in the high frequency limit of the Fourier transform of $p (t)$ for bounded $∣ p (t) ∣$ . An effective action, which is consistent with the non-adiabatic limit of Berry's phase, combined with the Bjorken-Johnson-Low prescription gives normal equal-time space-time commutators and no chiral anomaly. In contrast, an effective action with a monopole at the origin of the momentum space, which describes Berry's phase in the precise adiabatic limit but fails off the adiabatic limit, gives anomalous space-time commutators and a covariant anomaly to the gauge current. We regard this anomaly as an artifact of the postulated monopole and not a consequence of Berry's phase. As for the recent application of the chiral anomaly to the description of effective Weyl fermions in condensed matter and nuclear physics, which is closely related to the formulation of lattice chiral fermions, we point out that the chiral anomaly for each species doubler separately vanishes for a finite lattice spacing, contrary to the common assumption. Instead a general form of pair creation associated with the spectral flow for the Dirac sea with finite depth takes place. This view is supported by the Ginsparg-Wilson fermion, which defines a single Weyl fermion without doublers on the lattice and gives a well-defined index (anomaly) even for a finite lattice spacing.
↳ hep-thcond-mat.mes-hallnucl-thPRD(2018)·12 citations
10
Three-body Unitarity in the Finite Volume
M. Mai🇺🇸 · M. Döring🇺🇸
The physical interpretation of lattice QCD simulations, performed in a small volume, requires an extrapolation to the infinite volume. A method is proposed to perform such an extrapolation for three interacting particles at energies above threshold. For this, a recently formulated relativistic $3 \to 3$ amplitude based on the isobar formulation is adapted to the finite volume. The guiding principle is two- and three-body unitarity that imposes the imaginary parts of the amplitude in the infinite volume. In turn, these imaginary parts dictate the leading power-law finite-volume effects. It is demonstrated that finite-volume poles arising from the singular interaction, from the external two-body sub-amplitudes, and from the disconnected topology cancel exactly leaving only the genuine three-body eigenvalues. The corresponding quantization condition is derived for the case of three identical scalar-isoscalar particles and its numerical implementation is demonstrated.
↳ hep-latnucl-thEPJA(2017)·231 citations
11
Ground States via Spectral Combing on a Quantum Computer
David B. Kaplan🇺🇸 · Natalie Klco🇺🇸 · Alessandro Roggero🇺🇸
A new method is proposed for determining the ground state wave function of a quantum many-body system on a quantum computer, without requiring an initial trial wave function that has good overlap with the true ground state. The technique of Spectral Combing involves entangling an arbitrary initial wave function with a set of auxiliary qubits governed by a time dependent Hamiltonian, resonantly transferring energy out of the initial state through a plethora of avoided level crossings into the auxiliary system. The number of avoided level crossings grows exponentially with the number of qubits required to represent the Hamiltonian, so that the efficiency of the algorithm does not rely on any particular energy gap being large. We give an explicit construction of the quantum gates required for the realization of this procedure and explore the results of classical simulations of the algorithm on a small quantum computer with up to 8 qubits. We show that for certain systems and comparable results, Spectral Combing requires fewer quantum gates to realize than the Quantum Adiabatic Algorithm.
↳ quant-phhep-latnucl-th47 citations
12
General structure of fermion two-point function and its spectral representation in a hot magnetised medium
Aritra Das🇮🇳 · Aritra Bandyopadhyay🇮🇳 · Pradip K. Roy🇮🇳 · Munshi G. Mustafa🇮🇳
We have systematically constructed the general structure of the fermion self-energy and the effective quark propagator in presence of a nontrivial background like hot magnetised medium. This is applicable to both QED and QCD. The hard thermal loop approximation has been used for the heat bath. We have also examined transformation properties of the effective fermion propagator under some of the discrete symmetries of the system. Using the effective fermion propagator we have analysed the fermion dispersion spectra in a hot magnetised medium along with the spinor for each fermion mode obtained by solving the modified Dirac equation. The fermion spectra is found to reflect the discrete symmetries of the two-point functions. We note that for a chirally symmetric theory the degenerate left and right handed chiral modes in vacuum or in a heat bath get separated and become asymmetric in presence of magnetic field without disturbing the chiral invariance. The obtained general structure of the two-point functions is verified by computing the three-point function, which agrees with the existing results in one-loop order. Finally, we have computed explicitly the spectral representation of the two-point functions which would be very important to study the spectral properties of the hot magnetised medium corresponding to QED and QCD with background magnetic field.
↳ hep-phhep-latnucl-thPRD(2018)·31 citations
13
Quenching the CME via the gravitational anomaly and holography
Karl Landsteiner🇪🇸 · Esperanza Lopez🇪🇸 · Guillermo Milans del Bosch🇪🇸
In the presence of a gravitational contribution to the chiral anomaly, the chiral magnetic effect induces an energy current proportional to the square of the temperature in equilibrium. In holography the thermal state corresponds to a black hole. We numerically study holographic quenches in which a planar shell of scalar matter falls into a black hole and rises its temperature. During the process the momentum density (energy current) is conserved. The energy current has two components, a non-dissipative one induced by the anomaly and a dissipative flow component. The dissipative component can be measured via the drag it asserts on an additional auxiliary color charge. Our results indicate strong suppression very far from equilibrium.
↳ hep-thcond-mat.mes-hallhep-phnucl-thPRL(2018)·18 citations
14
Standard convolution description of deuteron tensor spin structure
W. Cosyn🇧🇪 · Yu-Bing Dong🇨🇳 · S. Kumano🇯🇵 · M. Sargsian🇺🇸
Spin-1 hadrons have additional structure functions not present for spin 1/2 hadrons. These could probe novel aspects of hadron structure and QCD dynamics. For the deuteron, the tensor structure function $b_{1}$ inherently mixes quark and nuclear degrees of freedom. These proceedings discuss two standard convolution models applied to calculations of the deuteron $b_{1}$ structure functions. We find large differences with the existing HERMES data and other convolution model calculations. This leaves room for non-standard contributions to $b_{1}$ in the deuteron. We also discuss the influence of higher twist nuclear effects in the model calculations and data extraction at kinematics covered in HERMES and Jefferson Lab.
↳ hep-phnucl-thPoS(2018)·0 citations
15
Dynamical vs geometric anisotropy in relativistic heavy-ion collisions: which one prevails?
L.V. Bravina🇷🇺 · I.P. Lokhtin🇷🇺 · L.V. Malinina🇷🇺 · S.V. Petrushanko🇷🇺 · A.M. Snigirev🇷🇺 · E.E. Zabrodin🇷🇺
We study the influence of geometric and dynamical anisotropies on the development of flow harmonics and, simultaneously, on the second- and third-order oscillations of femtoscopy radii. The analysis is done within the Monte Carlo event generator HYDJET++, which was extended to dynamical triangular deformations. It is shown that the merely geometric anisotropy provides the results which anticorrelate with the experimental observations of either $v_{2}$ (or $v_{3}$ ) or second-order (or third-order) oscillations of the femtoscopy radii. Decays of resonances significantly increase the emitting areas but do not change the phases of the radii oscillations. In contrast to the spatial deformations, the dynamical anisotropy alone provides the correct qualitative description of the flow and the femtoscopy observables simultaneously. However, one needs both types of the anisotropy to match quantitatively the experimental data.
↳ hep-phnucl-exnucl-thEPJA(2017)·14 citations

Affiliations

first authorsco-authorsvia INSPIRE