Nuclear Theory·nucl-th

Wednesday·September 4, 2019

18 papers—6 primary·12 cross-listed

07
[Submitted on 30 Aug 2019] (cross-list from hep-ph)
Low- $Q^{2}$ empirical parametrizations of the $N^{*}$ helicity amplitudes
G. Ramalho🇧🇷
The data associated with the electromagnetic excitations of the nucleon ( $γ^{*} N \to N^{*}$ ) are usually parametrized by helicity amplitudes at the resonance $N^{*}$ rest frame. The properties of the $γ^{*} N \to N^{*}$ transition current at low $Q^{2}$ can be, however, better understood when expressed in terms of structure form factors, particularly near the pseudothreshold, when the magnitude of the photon three-momentum vanishes ( $∣ q ∣ = 0$ ). At the pseudothreshold the invariant four-momentum square became $q^{2} = (M_{R} - M_{N})^{2}$ , well in the timelike region $Q^{2} = - q^{2} < 0$ [ $M_{N}$ and $M_{R}$ are the mass of the nucleon and of the resonance, respectively]. In the helicity amplitude representation, the amplitudes have well-defined dependences on $∣ q ∣$ , near the pseudothreshold, and there are correlations between different amplitudes. Those constraints are often ignored in the empirical parametrizations of the helicity amplitudes. In the present work, we show that the structure of the transition current near the pseudothreshold has an impact on the parametrizations of the data. We present a method which modifies analytic parametrizations of the data at low $Q^{2}$ , in order to take into account the constraints of the transition amplitudes near the pseudothreshold. The model dependence of the parametrizations on the low- $Q^{2}$ data is studied in detail.
Comments:
Published at Phys. Rev. D. 17 pages, 4 figures and 13 tables. Extended introduction. Extended bibliography. Parametrizations redefined in terms of an alternative but equivalent variable
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1909.00013 [pdf]
PRD(2019)·16 citations
08
[Submitted on 31 Aug 2019] (cross-list from hep-ph)
Improved pion mean fields and masses of singly heavy baryons
June-Young Kim🇰🇷 · Hyun-Chul Kim🇰🇷
A singly heavy baryon can be viewed as $N_{c} - 1$ ( $N_{c}$ as the number of colors) light valence quarks bound by the pion mean fields that are created by the presence of the $N_{c} - 1$ valence quarks self-consistently, while the heavy quark inside a singly heavy baryon is regarded as a static color source. We investigate how the pion mean fields are created by the presence of $N_{c}$ , $N_{c} - 1$ , and $N_{c} - 2$ light valence quarks, which correspond to the systems of light baryons, singly heavy baryons, and doubly heavy baryons. As the number of color decreases from $N_{c}$ to $N_{c} - 1$ , the pion mean fields undergo changes. As a result, the valence-quark contributions to the moments of inertia of the soliton become larger than the case of the $N_{c}$ valence quarks, whereas the sea-quark contributions decrease systematically. On the other hand, the presence of the $N_{c} - 2$ valence quarks is not enough to produce the strong pion mean fields, which leads to the fact that the classical soliton can not be formed. It indicates that the pion mean-field approach is not suitable to describe doubly heavy baryons. We show that the mass spectra of the singly heavy baryons are better described by the improved pion mean fields, compared with the previous work in which the pion mean fields are assumed to be intact with $N_{c}$ varied.
Comments:
18 pages, 4 figures. The final version for publication in PTEP
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
1909.00123 [pdf]
PTEP(2020)·15 citations
09
[Submitted on 31 Aug 2019] (cross-list from hep-ph)
Relaxation time for quark spin and thermal vorticity alignment in heavy-ion collisions
Alejandro Ayala🇲🇽 · David de la Cruz🇲🇽 · S. Hernández-Ortíz🇲🇽 · L. A. Hernández🇲🇽 · Jordi Salinas🇲🇽
We compute the relaxation time for quark/antiquark spin and thermal vorticity alignment in a quark-gluon plasma at finite temperature and quark chemical potential. We model the interaction of quark/antiquark spin with thermal vorticity as driven by a phenomenological modification of the elementary quark interaction with gluons. We find that in a scenario where the angular velocity of the quark-gluon plasma produced in a peripheral heavy-ion collision is small, quarks/antiquarks take a long time to align their spin with the vorticity. However, when the angular velocity created in the reaction is large, the alignment is efficient and well within the lifetime of the system created in the reaction. The relaxation time is larger for antiquarks which points out to a difference for the polarization of hadrons and antihadrons when this alignment is preserved during hadronization.
Comments:
6 pages, 6 figures, discussion extended, version accepted for publication in Physics Letters B
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1909.00274 [pdf]
PLB(2020)·38 citations
10
[Submitted on 1 Sept 2019] (cross-list from hep-ph)
Coupled-channel approach in hadron-hadron scattering
J.A. Oller🇪🇸
Coupled-channel dynamics for scattering and production processes in partial-wave amplitudes is discussed from a perspective that emphasizes unitarity and analyticity. We elaborate on several methods that have driven to important results in hadron physics, either by themselves or in conjunction with effective field theory. We also develop and compare with the use of the Lippmann-Schwinger equation in near-threshold scattering. The final(initial)-state interactions are discussed in detail for the elastic and coupled-channel case. Emphasis has been put in the derivation and discussion of the methods presented, with some applications examined as important examples of their usage.
Comments:
104 pages, 9 figures. Invited review article for Prog. Part. Nucl. Phys
Subjects:
High Energy Physics — Phenomenology (hep-ph); Quantum Gases (cond-mat.quant-gas); Nuclear Theory (nucl-th)
arXiv:
1909.00370 [pdf]
PPNP(2020)·77 citations
11
[Submitted on 1 Sept 2019] (cross-list from hep-lat)
Nucleon axial, tensor and scalar charges and $σ$ -terms in lattice QCD
C. Alexandrou (Univ. of Cyprus & The Cyprus Inst.) · S. Bacchio (The Cyprus Inst.) · M. Constantinou (Temple Univ.) · K. Hadjiyiannakou (The Cyprus Inst.) · K. Jansen (DESY-Zeuthen) · G. Koutsou (The Cyprus Inst.) · A. Vaquero Aviles-Casco (Univ. of Utah)
We determine the nucleon axial, scalar and tensor charges within lattice Quantum Chromodynamics including all contributions from valence and sea quarks. We analyze three gauge ensembles simulated within the twisted mass formulation at approximately physical value of the pion mass. Two of these ensembles are simulated with two dynamical light quarks and lattice spacing $a = 0.094$ ~fm and the third with $a = 0.08$ ~fm includes in addition the strange and charm quarks in the sea. After comparing the results among these three ensembles, we quote as final values our most accurate analysis using the latter ensemble. For the nucleon isovector axial charge we find $1.286 (23)$ in agreement with the experimental value. We provide the flavor decomposition of the intrinsic spin $\frac{1}{2} Δ Σ^{q}$ carried by quarks in the nucleon obtaining for the up, down, strange and charm quarks $\frac{1}{2} Δ Σ^{u} = 0.431 (8)$ , $\frac{1}{2} Δ Σ^{d} = - 0.212 (8)$ , $\frac{1}{2} Δ Σ^{s} = - 0.023 (4)$ and $\frac{1}{2} Δ Σ^{c} = - 0.005 (2)$ , respectively. The corresponding values of the tensor and scalar charges for each quark flavor are also evaluated providing valuable input for experimental searches for beyond the standard model physics. In addition, we extract the nucleon $σ$ -terms and find for the light quark content $σ_{π N} = 41.6 (3.8)$ ~MeV and for the strange $σ_{s} = 45.6 (6.2)$ ~MeV. The y-parameter that is used in phenomenological studies we find $y = 0.078 (7)$ .
Comments:
Expanded version as accepted in Phys. Rev. D.20 pages and 20 figures
Subjects:
High Energy Physics — Lattice (hep-lat); High Energy Physics — Experiment (hep-ex); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1909.00485 [pdf]
PRD(2020)·158 citations
12
[Submitted on 2 Sept 2019] (cross-list from hep-th)
Analytic self-gravitating $4$ -Baryons, traversable NUT-AdS wormholes, flat space-time multi-Skyrmions at finite volume and a novel transition in the $S U (3)$ -Skyrme model
Eloy Ayón-Beato🇲🇽 · Fabrizio Canfora🇨🇱 · Marcela Lagos🇨🇱 · Julio Oliva🇨🇱 · Aldo Vera🇨🇱
We construct the first analytic self-gravitating Skyrmions with higher Baryon charge in four dimensions for the $S U (3)$ -Skyrme-Einstein- $Λ$ theory by combining the generalized hedgehog ansatz with the approach developed by Balachandran et al. to describe the first (numerical) example of a non-embedded solution. These are genuine $S U (3)$ analytic solutions instead of trivial embeddings of $S U (2)$ into $S U (3)$ and its geometry is that of a Bianchi IX Universe. The Skyrme ansatz is chosen in such a way that the Skyrme field equations are identically satisfied in the sector with Baryon charge 4. The field equations reduce to a dynamical system for the three Bianchi IX scale factors. Particular solutions are explicitly analyzed. Traversable wormholes with NUT-AdS asymptotics supported by a topologically non-trivial $S U (3)$ -sigma soliton are also constructed. The self-gravitating solutions admit also a suitable flat limit giving rise to Skyrmions of charge 4 confined in a box of finite volume maintaining the integrability of the $S U (3)$ Skyrme field equations. This formalism discloses a novel transition at finite Baryon density arising from the competition between embedded and non-embedded solutions in which the non-embedded solutions prevail at high density while are suppressed at low densities.
Comments:
9 pages, 3 figures. Clarifications added, typos corrected. Accepted for publication in EPJC
Subjects:
High Energy Physics — Theory (hep-th); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1909.00540 [pdf]
EPJC(2020)·38 citations
13
[Submitted on 2 Sept 2019] (cross-list from hep-ph)
Temperatures and chemical potentials at kinetic freeze-out in relativistic heavy ion collisions from coarse grained transport simulations
Gabriele Inghirami🇫🇮 · Paula Hillmann🇩🇪 · Boris Tomášik🇸🇰 · Marcus Bleicher🇩🇪
Using the UrQMD/coarse graining approach we explore the kinetic freeze-out stage in central Au + Au collisions at various energies. These studies allow us to obtain detailed information on the thermodynamic properties (e.g. temperature and chemical potential) of the system during the kinetic decoupling stage. We explore five relevant collision energies in detail, ranging from $s_{N N} = 2.4 GeV$ (GSI-SIS) to $s_{N N} = 200 GeV$ (RHIC). By adopting a standard Hadron Resonance Gas equation of state, we determine the average temperature $⟨ T ⟩$ and the average baryon chemical potential $⟨ μ_{B} ⟩$ on the space-time hyper-surface of last interaction. The results highlight the nature of the kinetic freeze-out as a continuous process. This differential decoupling is an important aspect often missed when summarizing data as single points in the phase diagram as e.g. done in Blast-Wave fits. We compare the key properties of the system derived by using our approach with other models and we briefly review similarities and differences.
Comments:
Version accepted by JPG
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1909.00643 [pdf]
J.Phys.G(2020)·15 citations
14
[Submitted on 2 Sept 2019] (cross-list from hep-lat)
Hermitizing the HAL QCD potential in the derivative expansion
Sinya Aoki🇯🇵 · Takumi Iritani🇯🇵 · Koichi Yazaki🇯🇵
A formalism is given to hermitize the HAL QCD potential, which needs to be non-hermitian except the leading order (LO) local term in the derivative expansion as the Nambu-Bethe-Salpeter (NBS) wave functions for different energies are not orthogonal to each other. It is shown that the non-hermitian potential can be hermitized order by order to all orders in the derivative expansion. In particular, the next-to-leading order (NLO) potential can be exactly hermitized without approximation. The formalism is then applied to a simple case of $ΞΞ (^{1} S_{0})$ scattering, for which the HAL QCD calculation is available to the NLO. The NLO term gives relatively small corrections to the scattering phase shift and the LO analysis seems justified in this case. We also observe that the local part of the hermitized NLO potential works better than that of the non-hermitian NLO potential. The hermitian version of the HAL QCD potential is desirable for comparing it with phenomenological interactions and also for using it as a two-body interaction in many body systems.
Comments:
20 pages, 8 figures, appendix added with some other modifications for the published version
Subjects:
High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:
1909.00656 [pdf]
PTEP(2020)·4 citations
15
[Submitted on 3 Sept 2019] (cross-list from hep-lat)
Chiral-spin symmetry of the meson spectral function above $T_{c}$
C. Rohrhofer🇯🇵 · Y. Aoki🇯🇵 · L. Ya. Glozman🇦🇹 · S. Hashimoto🇯🇵
Recently, via calculation of spatial correlators of $J = 0, 1$ isovector operators using a chirally symmetric Dirac operator within $N_{F} = 2$ QCD, it has been found that QCD at temperatures $T_{c} - 3 T_{c}$ is approximately $S U (2)_{C S}$ and $S U (4)$ symmetric. The latter symmetry suggests that the physical degrees of freedom are chirally symmetric quarks bound by the chromoelectric field into color singlet objects without chromomagnetic effects. This regime of QCD has been referred to as a Stringy Fluid. Here we calculate correlators for propagation in time direction at a temperature slightly above $T_{c}$ and find the same approximate symmetries. This means that the meson spectral function is chiral-spin and $S U (4)$ symmetric.
Comments:
10 pages, 3 figures. Version published by PLB
Subjects:
High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
1909.00927 [pdf]
PLB(2020)·51 citations
16
[Submitted on 3 Sept 2019] (cross-list from astro-ph.HE)
Non-Newtonian gravity in strange quark stars and constraints from the observations of PSR J0740+6620 and GW170817
Shu-Hua Yang🇨🇳 · Chun-Mei PI🇨🇳 · Xiao-Ping Zheng🇨🇳 · Fridolin Weber🇺🇸
We investigate the effects of non-Newtonian gravity on the properties of strange quark stars (QSs) and constrain the parameters of the standard MIT bag model used to describe strange quark matter (SQM) by employing the mass of PSR J0740+6620 and the tidal deformability of GW170817. We find that, for the standard MIT bag model, these mass and tidal deformability observations would rule out the existence of QSs if non-Newtonian gravity effects are ignored. For a strange quark mass of $m_{s} = 95$ MeV, we find that QSs can exist for values of the non-Newtonian gravity parameter $g^{2} / μ^{2}$ in the range of 1.37 GeV $^{- 2} \leq g^{2} / μ^{2} \leq$ 7.28 GeV $^{- 2}$ and limits on the bag constant and the strong interaction coupling constant of the SQM model given by 141.3 MeV $\leq B^{1/4} \leq$ 150.9 MeV and $α_{S} \leq 0.56$ . For a strange quark mass of $m_{s} = 150$ MeV, QSs can exist for 1.88 GeV $^{- 2} \leq g^{2} / μ^{2} \leq$ 6.27 GeV $^{- 2}$ and limits on the parameters of the SQM model given by 139.7 MeV $\leq B^{1/4} \leq$ 147.3 MeV and $α_{S} \leq 0.49$ .
Comments:
ApJ accepted, 9 pages, 4 figures
Subjects:
High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Theory (nucl-th)
arXiv:
1909.00933 [pdf]
ApJ(2020)·20 citations
17
[Submitted on 3 Sept 2019] (cross-list from hep-ph)
QCD at finite isospin density: chiral perturbation theory confronts lattice data
Prabal Adhikari🇺🇸 · Jens O. Andersen🇳🇴
We consider the thermodynamics of three-flavor QCD in the pion-condensed phase at nonzero isospin chemical potential ( $μ_{I}$ ) and vanishing temperature using chiral perturbation theory in the isospin limit. The transition from the vacuum phase to a superfluid phase with a Bose-Einstein condensate of charged pions is shown to be second order and takes place at $μ_{I} = m_{π}$ . We calculate the pressure, isospin density, and energy density to next-to-leading order in the low-energy expansion. Our results are compared with recent high-precision lattice simulations as well as previously obtained results in two-flavor chiral perturbation theory. The agreement between the lattice results and the predictions from three-flavor chiral perturbation theory is very good for $μ_{I} < 200$ MeV. For larger values of $μ_{I}$ , the agreement between lattice data and the two-flavor predictions is surprisingly good and better than with the three-flavor predictions. Finally, in the limit $m_{s} ≫ m_{u} = m_{d}$ , we show that the three-flavor observables reduce to the two-flavor observables with renormalized parameters. The disagreement between the results for two-flavor and three-flavor $χ$ PT can largely be explained by the differences in the measured low-energy constants.
Comments:
8 pages and 4 figs. v2: Expanded discussion, in particular the matching between two- and three flavor couplings for large strange-quark masses. Matches published version
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1909.01131 [pdf]
PLB(2020)·50 citations
18
[Submitted on 3 Sept 2019] (cross-list from gr-qc)
Cooling binary neutron star remnants via nucleon-nucleon-axion bremsstrahlung
Tim Dietrich🇳🇱 · Katy Clough🇬🇧
The QCD axion is a hypothetical particle motivated by the Strong CP problem of particle physics. One of the primary ways in which its existence can be inferred is via its function as an additional cooling channel in stars, with some of the strongest constraints coming from the supernova observation SN1987A. Multimessenger observations of binary neutron star mergers (such as those of GW170817, AT2017gfo, and GRB170817A) may provide another scenario in which such constraints could be obtained. In particular, the axion could potentially alter the lifetime, the ejection of material, and the emitted gravitational wave signal of the postmerger remnant. In this article, we perform numerical relativity simulations of a binary neutron star merger, including a phenomenological description of the nucleon-nucleon-axion bremsstrahlung to quantify the effects of such a cooling channel on the dynamical evolution. While our simulations show a difference in the temperature profile of the merger remnant, the imprint of the axion via nucleon-nucleon-axion bremsstrahlung on the emitted gravitational wave signal and the ejecta mass is too small to improve constraints on the axion mass with current or future planned detectors. Whilst we consider a limited number of cases, and a simplified cooling model, these broadly represent the "best case" scenario, thus, a more thorough investigation is unlikely to change the conclusions, at least for this particular interaction channel.
Subjects:
General Relativity and Quantum Cosmology (gr-qc); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1909.01278 [pdf]
PRD(2019)·40 citations

Affiliations

first authorsco-authorsvia INSPIRE