Nuclear Theory·nucl-th

Tuesday·December 19, 2023

25 papers—12 primary·13 cross-listed

13
Gravitational form factors of the nucleon and one pion graviproduction in chiral EFT
H. Alharazin🇩🇪
In the framework of chiral effective field theory of delta resonances, nucleons and pions interacting with background gravitational field we calculate the gravitational form factors of the nucleon up to fourth order in the small scale expansion and obtain the long-range behavior of the corresponding contributions to the energy, spin, pressure and shear force distributions. By comparing nucleon gravitational form factors with and without delta contributions we conclude that explicit inclusion of deltas plays an important role. Next we explore the Lorentz structure of the $N \mapsto N π$ transition matrix element of the conserved symmetric energy-momentum tensor and introduce its parametrization in terms of twelve transition form factors. We use the chiral effective field theory to calculate the tree-order contributions to the gravitational transition form factors of the pion graviproduction off the nucleon up to third order.
↳ hep-phhep-thnucl-thPRD(2024)·15 citations
14
Pre-equilibrium photon production in QCD Kinetic Theory
Oscar Garcia-Montero🇩🇪 · Aleksas Mazeliauskas🇩🇪 · Philip Plaschke🇩🇪 · Sören Schlichting🇩🇪
We use QCD kinetic theory to compute photon production in the chemically equilibrating Quark-Gluon Plasma created in the early stages of high-energy heavy-ion collisions. We show that the photon spectrum radiated from an attractor evolution satisfies a simple scaling form in terms of the specific shear viscosity $η / s$ and entropy density $d S / d ζ \sim (T τ^{1/3})^{3/2}_{\infty}$ . We confirm the analytical predictions with numerical kinetic theory simulations. We use the extracted scaling function to compute the pre-equilibrium photon contribution in $s_{N N} = 2.76 TeV$ 0-20% PbPb collisions. We demonstrate that our matching procedure allows for a smooth switching from pre-equilibrium kinetic to thermal hydrodynamic photon production.
↳ hep-phnucl-thPoS(2024)·1 citation
15
Lattice QCD studies of the $Δ$ baryon resonance and the $K_{0}^{*} (700)$ and $a_{0} (980)$ meson resonances: the role of exotic operators in determining the finite-volume spectrum
John Bulava🇺🇸 · Danny Darvish🇩🇪 · Andrew D. Hanlon🇺🇸 · Ben Hörz🇺🇸 · Colin Morningstar🇩🇪 · Amy Nicholson🇺🇸 · Fernando Romero-López🇺🇸 · Sarah Skinner🇺🇸 · Pavlos Vranas🇺🇸 · André Walker-Loud🇺🇸
Studies of the $Δ$ baryon resonance and the $K_{0}^{*} (700)$ and $a_{0} (980)$ meson resonances using $N_{f} = 2 + 1$ lattice QCD for pion masses near 200 MeV are presented. The $s$ -wave scattering lengths for both the $I = 1/2$ $N π$ and $I = 3/2$ $N π$ channels and properties of the $Δ$ resonance are identified from the finite-volume energy levels of the lattice simulation. The importance of a three-quark $Δ$ -operator in the $N π$ system and tetraquark operators in the mesonic systems is investigated.
↳ hep-latnucl-thPoS(2024)·4 citations
16
The 95 GeV Excess in the Georgi-Machacek Model: Single or Twin Peak Resonance
Amine Ahriche (Sharjah U., UAE)🇦🇪
In this work, we investigate the possibility to address the excess observed around 95 GeV in the $γ γ$ , $τ τ$ , and $b b ˉ$ channels as a scalar resonance(s) within the Georgi-Machacek (GM) model. In our analysis, we find that the excess can be easily accommodated in the channels ( $γ γ$ and $b b ˉ$ ) simultaneously, where the 95 GeV candidate is a single peak resonance (SPR) due to a light CP-even scalar. We found that the excess in the $τ τ$ channel can be addressed simultaneously with $γ γ$ and $b b ˉ$ only if the 95 GeV candidate is a twin peak resonance (TPR), i.e., another CP-odd scalar in addition to the CP-even scalar. We demonstrate that the nature of the 95 GeV scalar resonance candidate (SPR or TPR) can be probed via the properties of its di- $τ$ decay.
↳ hep-phhep-exnucl-thPRD(2024)·38 citations
17
About the magnitude of the $γ^{*} N \to N (1520)$ transverse amplitudes near $Q^{2} = 0$
G. Ramalho🇰🇷
The $γ^{*} N \to N (1520)$ transition has a property that differs from the other low-lying nucleon resonance amplitudes: the magnitude of the transverse helicity amplitudes.The transition helicity amplitudes are defined in terms of square-transfer momentum $q^{2}$ , or $Q^{2} = - q^{2}$ . Near the photon point ( $Q^{2} = 0$ ) there is a significant difference in the magnitude of the transverse amplitudes: $A_{3/2}$ is very large and $A_{1/2}$ is very small. This atypical behavior contrasts with the relation between the amplitudes at the pseudothreshold [the limit where the nucleon and the $N (1520)$ are both at rest and $Q^{2} < 0$ ], where $A_{3/2} = A_{1/2} / 3$ , and also in the large- $Q^{2}$ region, where theory and data suggest that $A_{3/2}$ is suppressed relative to $A_{1/2}$ . In the present work, we look for the source of the suppression of the $A_{1/2}$ amplitude at $Q^{2} = 0$ . The result is easy to understand in first approximation, when we look into the relation between the transverse amplitudes and the elementary form factors, defined by a gauge-invariant parametrization of the $γ^{*} N \to N (1520)$ transition current, near $Q^{2} = 0$ . There is a partial cancellation between contributions of two elementary form factors near $Q^{2} = 0$ . We conclude, however, that the correlation between the two elementary form factors at $Q^{2} = 0$ is not sufficient to explain the transverse amplitude data below $Q^{2} = 1$ GeV $^{2}$ . The description of the dependence of the transverse amplitudes on $Q^{2}$ requires the determination of the scale of variation of the elementary form factors in the range $Q^{2} = 0$ ...0.5 GeV $^{2}$ ,a region with almost non existent data. We conclude at the end that the low- $Q^{2}$ data for the transverse amplitudes can be well described when we relate the scale of variation of the elementary form factors with the nucleon dipole form factor.
↳ hep-phhep-exhep-latnucl-ex+1PRD(2024)·1 citation
18
Superconducting phases of strongly-interacting matter in large magnetic fields
Geraint W. Evans🇬🇧
The large magnetic fields of neutron stars and produced in heavy-ion collisions motivate investigation into the response of strongly-interacting matter to extreme magnetic forces beyond just theoretical interest. Furthermore, the varying temperature $T$ , baryon chemical potential $μ_{B}$ , and aforementioned magnetic fields $B$ , of these systems leads to questions concerning the phase structure of Quantum Chromodynamics (QCD) at large. At low temperatures, superconducting phases become a possible candidate for the ground state in the $μ_{B}$ - $B$ plane. This thesis investigates two scenarios where these phases emerge at $T = 0$ , with an emphasis on the type-II regime. Preceding the presentation of these works, the $μ_{B}$ - $B$ plane of the QCD phase diagram is reviewed such that the results can be placed in the wider context of this plane.
↳ hep-phhep-thnucl-th0 citations
19
Systematic Improvement of $x$ -dependent Unpolarized Nucleon Generalized Parton Distribution in Lattice-QCD Calculation
Jack Holligan🇺🇸 · Huey-Wen Lin🇺🇸
We present a first study of the effects of renormalization-group resummation (RGR) and leading-renormalon resummation (LRR) on the systematic errors of the unpolarized isovector nucleon generalized parton distribution in the framework of large-momentum effective theory (LaMET). This work is done using lattice gauge ensembles generated by the MILC collaboration, consisting of 2+1+1 flavors of highly improved staggered quarks with a physical pion mass at lattice spacing $a \approx 0.09$ fm and a box width $L \approx 5.76$ fm. We present results for the nucleon $H$ and $E$ GPDs with average boost momentum $P_{z} \approx 2$ GeV at momentum transfers $Q^{2} = [0, 0.97]$ GeV $^{2}$ at skewness $ξ = 0$ as well as $Q^{2} \in 0.23$ GeV $^{2}$ at $ξ = 0.1$ , renormalized in the $MS$ scheme at scale $μ = 2.0$ GeV, with two- and one-loop matching, respectively. We demonstrate that the simultaneous application of RGR and LRR significantly reduces the systematic errors in renormalized matrix elements and distributions for both the zero and nonzero skewness GPDs, and that it is necessary to include both RGR and LRR at higher orders in the matching and renormalization processes.
↳ hep-lathep-phnucl-thPRD(2024)·29 citations
20
Non-Abelian chiral soliton lattice in rotating QCD matter: Nambu-Goldstone and excited modes
Minoru Eto🇯🇵 · Kentaro Nishimura🇯🇵 · Muneto Nitta🇯🇵
The ground state of QCD with two flavors at a finite baryon chemical potential under rapid rotation is a chiral soliton lattice (CSL) of the $η$ meson, consisting of a stack of sine-Gordon solitons carrying a baryon number, due to the anomalous coupling of the $η$ meson to the rotation. In a large parameter region, the ground state becomes a non-Abelian CSL, in which due to the neutral pion condensation each $η$ soliton decays into a pair of non-Abelian sine-Gordon solitons carrying $S^{2}$ moduli originated from Nambu-Goldstone (NG) modes localized around it, corresponding to the spontaneously broken vector symmetry SU $(2)_{V}$ . There, the $S^{2}$ modes of neighboring solitons are anti-aligned, and these modes should propagate in the transverse direction of the lattice due to the interaction between the $S^{2}$ modes of neighboring solitons. In this paper, we calculate excitations including gapless NG modes and excited modes around non-Abelian and Abelian ( $η$ ) CSLs, and find three gapless NG modes with linear dispersion relations (type-A NG modes): two isospinons ( $S^{2}$ modes) and a phonon corresponding to the spontaneously broken vector SU $(2)_{V}$ and translational symmetries around the non-Abelian CSL, respectively, and only a phonon for the Abelian CSL because of the recovering SU $(2)_{V}$ . We also find in the deconfined phase that the dispersion relation of the isospinons becomes of the Dirac type, {\it i.~e.~} linear even at large momentum.
↳ hep-phhep-thnucl-thJHEP(2024)·21 citations
21
Acausality in truncated 'MIS'-type theory
Sukanya Mitra🇮🇳
The causal-stable Muller-Israel-Stewart (MIS) theory is known to have a finite number of out of equilibrium derivative order corrections but requires treating the viscosity tensor as a separate degree of freedom with its own equations of motion, apart from the fundamental fluid degrees of freedom like velocity and temperature. In this work, I will show that it is possible to rewrite the MIS theory only in terms of velocity and temperature, but the resultant constitutive relation for dissipation must include all orders of gradient corrections. In this work I will argue that an all-order resummation of gradient contributions is equivalent to introducing new `non-fluid' degrees of freedom in the MIS theory. It will also be shown, using the relativistic quantum causality condition, that any finitely truncated order of derivative correction, however high it is, leads to a theory that is acausal, unless the corrections are infinitely summed up to all orders.
↳ gr-qchep-phhep-thnucl-thPRD(2024)·10 citations
22
Limiting attractors in heavy-ion collisions
Kirill Boguslavski🇦🇹 · Aleksi Kurkela🇳🇴 · Tuomas Lappi🇫🇮 · Florian Lindenbauer🇦🇹 · Jarkko Peuron🇫🇮
We study universal features of the hydrodynamization process in heavy-ion collisions using QCD kinetic theory simulations for a wide range of couplings. We introduce the new concept of limiting attractors, which are obtained by extrapolation to vanishing and strong couplings. While the hydrodynamic limiting attractor emerges at strong couplings and is governed by the viscosity-related relaxation time scale $τ_{R}$ , we identify a bottom-up limiting attractor at weak couplings. It corresponds to the late stages of the perturbative bottom-up thermalization scenario and exhibits isotropization on the time scale $τ_{BMSS} = α_{s}^{- 13/5} / Q_{s}$ . In contrast to hydrodynamic limiting attractors, at finite couplings the bottom-up limiting attractor provides a good universal description of the pre-hydrodynamic evolution of jet and heavy-quark momentum broadening ratios $q^^{y y} / q^^{z z}$ and $κ_{T} / κ_{z}$ . We also provide parametrizations for these ratios for phenomenological studies of pre-equilibrium effects on jets and heavy quarks.
↳ hep-phnucl-thPLB(2024)·29 citations
23
Measurement of the Isolated Nuclear Two-Photon Decay in $^{72} Ge$
D. Freire-Fernández🇩🇪 · W. Korten🇫🇷 · R. J. Chen🇩🇪 · S. Litvinov🇩🇪 · Yu. A. Litvinov🇩🇪 · M. S. Sanjari🇩🇪 · H. Weick🇩🇪 · F. C. Akinci🇹🇷 · H. M. Albers🇩🇪 · M. Armstrong🇩🇪 · A. Banerjee🇩🇪 · K. Blaum🇩🇪 and 48 other authors
The nuclear two-photon or double-gamma ( $2 γ$ ) decay is a second-order electromagnetic process whereby a nucleus in an excited state emits two gamma rays simultaneously. To be able to directly measure the $2 γ$ decay rate in the low-energy regime below the electron-positron pair-creation threshold, we combined the isochronous mode of a storage ring with Schottky resonant cavities. The newly developed technique can be applied to isomers with excitation energies down to $\sim 100$ \,keV and half-lives as short as $\sim 10$ \,ms. The half-life for the $2 γ$ decay of the first-excited $0^{+}$ state in bare $^{72} Ge$ ions was determined to be $23.9 (6)$ \,ms, which strongly deviates from expectations.
↳ nucl-exnucl-thPRL(2024)·15 citations
24
Simultaneous minijets and QGP evolution
Charles Gale🇨🇦 · Sangyong Jeon🇨🇦 · Daniel Pablos🇪🇸 · Mayank Singh🇺🇸
Minijets traversing through the QGP formed in heavy-ion collisions deposit significant amount of energy in the bulk medium. They also create gradients in temperatures which alter the flow profile and enhance entropy production. We study the effects of minijets in a simultaneous hydro + jet framework and find that inclusion of minijets requires recalibration of transport properties extracted from the model-to-data comparisons.
↳ hep-phnucl-thEPJ Web Conf.(2024)·0 citations
25
Enhanced contribution of the pairing gap to the QCD equation of state at large isospin chemical potential
Yuki Fujimoto🇺🇸
I study QCD at large isospin density, which is known to be in the superfluid state with Cooper pairs carrying the same quantum number as pions. I solve the gap equation derived from the perturbation theory up to the next-to-leading order corrections. The pairing gap at large isospin chemical potential is found to be enhanced compared to the color-superconducting gap at large baryon chemical potential due to the $2$ difference in the exponent arising from the stronger attraction in one-gluon exchange in the singlet channel. Then, using the gap function, I evaluate the contribution of the condensation energy of the superfluid state to the QCD equation of state. At isospin chemical potential of a few GeV, where the lattice QCD and the perturbative QCD can be both applied, the effect of the condensation energy becomes dominant even compared to the next-to-leading order corrections to the pressure in the perturbation theory. It resolves the discrepancy between the recent lattice QCD results and the perturbative QCD result.
↳ hep-phhep-latnucl-thPRD(2024)·25 citations

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