Nuclear Theory·nucl-th

Tuesday·March 31, 2020

14 papers—4 primary·10 cross-listed

05
[Submitted on 27 Mar 2020] (cross-list from gr-qc)
Neutron star cooling in modified gravity theories
Akira Dohi · Ryotaro Kase · Rampei Kimura · Kazuhiro Yamamoto · Masa-aki Hashimoto
We study thermal evolution of isolated neutron stars in scalar-tensor theories for the first time. Whether the rapid cooling due to the direct Urca process occurs or not is an interesting question in the viewpoint of the temperature observation of isolated neutron stars. Moreover, investigation of the cooling effect of nucleon superfluidity also has the large uncertainties though it is important in modern cooling theory. The cooling effect is typically influenced by the proton fraction and the central density. If a fifth force is mediated due to modification of gravity, the relation between the central density and mass of neutron stars differs from one in general relativity, and the cooling curve is also naively expected to be varied. We find that an unscreened fifth force near the surface of neutron stars changes mass-central density relation, and the direct Urca process can be triggered even for neutron stars with smaller mass. We also present cooling curves including nucleon superfluidity under the scalar-tensor theory. These results show that it might be useful to test gravitational theories with cooling observations of neutron stars.
Comments:
34 pages, 35 figures; v2 - significantly revised with several additional calculations, accepted for publication in PTEP
Subjects:
General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Theory (nucl-th)
arXiv:
2003.12571 [pdf]
PTEP(2021)·10 citations
06
[Submitted on 27 Mar 2020] (cross-list from hep-ph)
Gravitational form factors of hyperons in light-cone QCD
U. Özdem🇹🇷 · K. Azizi🇮🇷
The quark parts of the gravitational form factors of hyperons are calculated by means of the light-cone QCD sum rule. In the calculations, the distribution amplitudes (DAs) of $Σ$ , $Ξ$ and $Λ$ together with the general forms of their interpolating currents as well as the quark part of the energy-momentum tensor current are used. These form factors can provide information on their mass and distributions of the angular momentum, energy and pressure inside the hyperons. It is obtained that the $Q^{2}$ dependencies of the hyperon gravitational form factors are nicely characterized by a multipole fit function. Using the fits of these form factors, some mechanical properties such as the mechanical radius of the hyperons and the pressure and energy distributions at the center of these particles are obtained. The obtained results can help us in better understanding of the internal structures of these baryons and the QCD as theory of the strong interaction.
Comments:
13 Pages, 2 Figures and 5 Tables
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); High Energy Physics — Lattice (hep-lat); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
2003.12588 [pdf]
PRD(2020)·13 citations
07
[Submitted on 27 Mar 2020] (cross-list from hep-ph)
Lensing Mechanism Meets Small- $x$ Physics: Single Transverse Spin Asymmetry in $p^{↑} + p$ and $p^{↑} + A$ Collisions
Yuri V. Kovchegov🇺🇸 · M. Gabriel Santiago🇺🇸
We calculate the single transverse spin asymmetry (STSA) in polarized proton-proton ( $p^{↑} + p$ ) and polarized proton-nucleus ( $p^{↑} + A$ ) collisions ( $A_{N}$ ) generated by a partonic lensing mechanism. The polarized proton is considered in the quark-diquark model while its interaction with the unpolarized target is calculated using the small- $x$ /saturation approach, which includes multiple rescatterings and small- $x$ evolution. The phase required for the asymmetry is caused by a final-state gluon exchange between the quark and diquark, as is standard in the lensing mechanism of Brodsky, Hwang and Schmidt. Our calculation combines the lensing mechanism with small- $x$ physics in the saturation framework. The expression we obtain for the asymmetry $A_{N}$ of the produced quarks has the following properties: (i) The asymmetry is generated by the dominant elastic scattering contribution and $1/ N_{c}^{2}$ suppressed inelastic contribution (with $N_{c}$ the number of quark colors); (ii) The asymmetry grows or oscillates with the produced quark's transverse momentum $p_{T}$ until the momentum reaches the saturation scale $Q_{s}$ , and then only falls off as $1/ p_{T}$ for larger momenta; (iii) The asymmetry decreases with increasing atomic number $A$ of the target for $p_{T}$ below or near $Q_{s}$ , but is independent of $A$ for $p_{T}$ significantly above $Q_{s}$ . We discuss how these properties may be qualitatively consistent with the data on $A_{N}$ published by the PHENIX collaboration and with the preliminary data on $A_{N}$ reported by the STAR collaboration.
Comments:
23 pages, 10 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
2003.12650 [pdf]
PRD(2020)·21 citations
08
[Submitted on 28 Mar 2020] (cross-list from hep-ph)
Functional renormalization group study of the critical region of the quark-meson model with vector interactions
Renan Câmara Pereira🇵🇹 · Rainer Stiele🇮🇹 · Pedro Costa🇵🇹
The critical region of the two flavour quark-meson model with vector interactions is explored using the Functional Renormalization Group technique, a non-perturbative method that takes into account quantum and thermal fluctuations. Special attention is given to the low temperature and high density region of the phase diagram, which is very important for the evolution of proto-neutron stars and to construct the equation of state of compact stars. As in previous studies, without repulsive vector interaction, an unphysical region of negative entropy density is found near the first order chiral phase transition. We explore the connection between this unphysical region and the chiral critical region, especially the first order line and spinodal lines, using also different values for vector interactions. The effect of finite vector interactions in the critical region is explored. We find that the unphysical negative entropy density region appears because the $s = 0$ isentropic line, near the critical region, is displaced from its $T = 0$ location. For certain values of vector interactions this region is pushed to lower temperatures and high chemical potentials in such way that the negative entropy density region on the phase diagram of the model can even disapear. In the case of finite vector interactions, the location of the critical end point has a non-trivial behaviour in the $T - μ_{B}$ plane, which differs from that in mean-field calculations.
Comments:
16 pages, 6 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2003.12829 [pdf]
EPJC(2020)·22 citations
09
[Submitted on 28 Mar 2020] (cross-list from hep-ph)
A Novel Feature of Valence Quark Distributions in Hadrons
Christopher Leon🇺🇸 · Misak M. Sargsian🇺🇸 · Frank Vera🇺🇸
Examining the evolution of the maximum of valence quark distribution weighted by Bjorken x, $h (x, t) \equiv x q_{V} (x, t)$ , we observe that $h (x, t)$ at the peak should become a one parameter function; $h (x_{p}, t) = Φ (x_{p} (t))$ , where $x_{p}$ is the position of the peak and $t = lo g Q^{2}$ . This observation is used to derive a new model independent relation which connects the partial derivative of the valence parton distribution functions (PDFs) in $x_{p}$ to the QCD evolution equation through the $x_{p}$ -derivative of the logarithm of the function $Φ (x_{p} (t))$ . A numerical analysis of this relation using empirical PDFs results in a observation of the exponential form of the $Φ (x_{p} (t)) = h (x_{p}, t) = C e^{D x_{p} (t)}$ for leading to next-to-next leading order approximations of PDFs for the all $Q^{2}$ range covering four orders in magnitude. The exponent, $D$ , of the observed "height-position" correlation function converges with the increase of the order of approximation. This result holds for all PDF sets considered. A similar relation is observed also for pion valence quark distribution, indicating that the obtained relation may be universal for any non-singlet partonic distribution. The observed "height - position" correlation is used also to indicate that no finite number exchanges can describe the analytic behavior of the valence quark distribution at the position of the peak at fixed $Q^{2}$ .
Comments:
6 pages and 7 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
2003.12902 [pdf]
MDPI Physics(2021)·4 citations
10
[Submitted on 30 Mar 2020] (cross-list from hep-ph)
Heavy baryons in holographic QCD with higher dimensional degrees of freedom
Daisuke Fujii🇯🇵 · Atsushi Hosaka🇯🇵
We try to introduce heavy flavors to Sakai-Sugimoto model by regarding higher dimensional components of gauge fields as heavy mesons. Using the Forgács and Manton approach, we obtain a theory composed of heavy mesons and the instanton of light flavors. Applying the collective coordinate quantization method, we derived a mass formula of heavy baryons. In the leading order of $1/ m_{H}$ expansion ( $m_{H}$ the mass of a heavy quark), we find singlet and doublet states in the heavy quark symmetry (HQS). Also, we obtain the degenerate Roper like and odd parity excitations. By virtue of heavy meson degrees of freedom, our mass formula reproduces the mass ordering of $Σ_{c}^{*}$ and $Λ_{c}^{*}$ correctly.
Comments:
9 pages, 2 tables
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
2003.13415 [pdf]
PRD(2020)·9 citations
11
[Submitted on 11 Mar 2020] (cross-list from cond-mat.mtrl-sci)
Elastic properties of phases with nonspherical nuclei in dense matter
C. J. Pethick · Zhaowen Zhang · D. N. Kobyakov
We consider the elastic constants of phases with nonspherical nuclei, so-called pasta phases, predicted to occur in the inner crust of a neutron star. First, we treat perfectly ordered phases and give numerical estimates for lasagna and spaghetti when the pasta elements are spatially uniform: the results are in order-of-magnitude agreement with the numerical simulations of Caplan, Schneider, and Horowitz, Phys. Rev. Lett. 121, 132701 (2018). We then turn to pasta phases without long-range order and calculate upper (Voigt) and lower (Reuss) bounds on the effective shear modulus and find that the lower bound is zero, but the upper bound is nonzero. To obtain better estimates, we then apply the self-consistent formalism and find that this predicts that the shear modulus of the phases without long-range order is zero if the pasta elements are spatially uniform. In numerical simulations, the pasta elements are found to be modulated spatially and we show that this modulation is crucial to obtaining a nonzero elastic moduli for pasta phases without long-range order. In the self-consistent formalism we find that, for lasagna, the effective shear modulus is linear in the elastic constants that do not vanish when the pasta elements are spatially uniform while, for spaghetti, it varies as the square root of these elastic constants. We also consider the behavior of the elastic constant associated with a homologous strain (hydrostatic compression) of the structure of the pasta phases without long-range order.
Comments:
9 pages, 6 figures
Subjects:
cond-mat.mtrl-sci (cond-mat.mtrl-sci); High Energy Astrophysical Phenomena (astro-ph.HE); cond-mat.other (cond-mat.other); Nuclear Theory (nucl-th)
arXiv:
2003.13430 [pdf]
PRC(2020)·36 citations
12
[Submitted on 30 Mar 2020] (cross-list from hep-th)
Similarity between the kinematic viscosity of quark-gluon plasma and liquids at the viscosity minimum
Matteo Baggioli🇬🇧 · Vadim Brazhkin🇷🇺 · Kostya Trachenko🇪🇸
Recently, it has been found that the kinematic viscosity of liquids at the minimum, $ν_{m}$ , can be expressed in terms of fundamental physical constants, giving $ν_{m}$ on the order of $1 0^{- 7} m^{2} /s$ . Here, we show that the kinematic viscosity of quark-gluon plasma (QGP) has a similar value and support this finding by experimental data and theoretical estimations. The similarity is striking, given that the dynamic viscosity and the density of QGP are about 16 orders of magnitude larger than in liquids and that the two systems have disparate interactions and fundamental theories. We discuss the implications of this result for understanding the QGP including the similarity of flow and particle dynamics at the viscosity minimum, the associated dynamical crossover and universality of shear diffusivity.
Comments:
v3: discussion about the dynamical crossover and the various approximations improved
Subjects:
High Energy Physics — Theory (hep-th); cond-mat.soft (cond-mat.soft); Nuclear Theory (nucl-th)
arXiv:
2003.13506 [pdf]
SciPost Phys.(2021)·16 citations
13
[Submitted on 30 Mar 2020] (cross-list from hep-ph)
Parameterization and applications of the low- $Q^{2}$ nucleon vector form factors
Kaushik Borah🇺🇸 · Richard J. Hill🇺🇸 · Gabriel Lee🇺🇸 · Oleksandr Tomalak🇺🇸
We present the proton and neutron vector form factors in a convenient parametric form that is optimized for momentum transfers $≲$ few GeV $^{2}$ . The form factors are determined from a global fit to electron scattering data and precise charge radius measurements. A new treatment of radiative corrections is applied. This parametric representation of the form factors, uncertainties and correlations provides an efficient means to evaluate many derived observables. We consider two classes of illustrative examples: neutrino-nucleon scattering cross sections at GeV energies for neutrino oscillation experiments and nucleon structure corrections for atomic spectroscopy. The neutrino-nucleon charged current quasielastic (CCQE) cross section differs by 3-5% compared to commonly used form factor models when the vector form factors are constrained by recent high-statistics electron-proton scattering data from the A1 Collaboration. Nucleon structure parameter determinations include: the magnetic and Zemach radii of the proton and neutron, $[r_{M}^{p}, r_{M}^{n}] = [0.739 (41) (23), 0.776 (53) (28)]$ fm and $[r_{Z}^{p}, r_{Z}^{n}] = [1.0227 (94) (51), - 0.0445 (14) (3)]$ fm; the Friar radius of nucleons, $[(r_{F}^{p})^{3}, (r_{F}^{n})^{3}] = [2.246 (58) (2), 0.0093 (6) (1)]$ fm $^{3}$ ; the electric curvatures, $[⟨ r^{4} ⟩_{E}^{p}, ⟨ r^{4} ⟩_{E}^{n}] = [1.08 (28) (5), - 0.33 (24) (3)]$ fm $^{4}$ ; and bounds on the magnetic curvatures, $[⟨ r^{4} ⟩_{M}^{p}, ⟨ r^{4} ⟩_{M}^{n}] = [- 2.0 (1.7) (0.8), - 2.3 (2.1) (1.1)]$ fm $^{4}$ . The first and dominant uncertainty is propagated from the experimental data and radiative corrections, and the second error is due to the fitting procedure.
Comments:
24 pages, 5 figures, journal version
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th); Atomic Physics (physics.atom-ph)
arXiv:
2003.13640 [pdf]
PRD(2020)·90 citations
14
[Submitted on 30 Mar 2020] (cross-list from hep-ph)
Thermal dilepton production in collisional hot QCD medium in the presence of chromo-turbulent fields
Lakshmi J. Naik🇮🇳 · V. Sreekanth🇮🇳 · Manu Kurian🇮🇳 · Vinod Chandra🇮🇳
The effects of collisional processes in the hot QCD medium to thermal dilepton production from $q q$ annihilation in relativistic heavy-ion collisions have been investigated. The non-equilibrium corrections to the momentum distribution function have been estimated within the framework of ensemble-averaged diffusive Vlasov-Boltzmann equation, encoding the effects of collisional processes and turbulent chromo-fields in the medium. The contributions from the $2 \to 2$ elastic scattering processes have been quantified for the thermal dilepton production rate. It is seen that the collisional corrections enhance the equilibrium dilepton spectra at high $p_{T}$ and suppress at lower $p_{T}$ . A comparative study between collisional and anomalous contributions to the dilepton production rates has also been explored. The collisional contributions are seen to be marginal over that due to collisionless anomalous transport.
Comments:
13 pages, 8 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2003.13645 [pdf]
J.Phys.G(2022)·7 citations

Affiliations

first authorsco-authorsvia INSPIRE