Nuclear Theory·nucl-th

Thursday·January 22, 2026

13 papers—5 primary·8 cross-listed

06
Neutron star cooling implications and magnetic field of the Vela Junior central compact object from all XMM-Newton and Chandra spectra
Wynn C. G. Ho (Haverford)🇺🇸 · Esther Simkhayeva (Haverford)🇺🇸 · Alexander Y. Potekhin (Ioffe Institute)🇷🇺
The central compact object (CCO) in the Vela Junior supernova remnant is a young neutron star whose relatively low X-ray flux and small distance suggest it has a mass high enough to activate fast neutrino cooling processes. Here we analyse all XMM-Newton MOS and pn and Chandra ACIS-S spectra of the Vela Junior CCO, with observations taking place over the 9 years from 2001 to 2010. We find that the best-fit flux and spectral model parameters do not vary significantly when treating each observation independently, and therefore we fit all the spectra simultaneously using various spectral models to characterize the predominantly thermal emission from the neutron star surface. Our results indicate the Vela Junior CCO has an atmosphere composed of hydrogen, a hot spot temperature (unredshifted) of 3.5x10^6 K, and a colder surface temperature of (6.6-8.8)x10^5 K. Possible absorption lines at ~0.6 keV and 0.9 keV provide evidence for the first-time of an average surface magnetic field B~3x10^10 G for this CCO, which is similar to the magnetic field of other CCOs. At the accurate new Vela Junior distance of 1.4 kpc, the observed luminosity that is dominated by the hot spot is ~5x10^32 erg s^-1. The luminosity from the rest of the colder surface is (1.3-4.0)x10^32 erg s^-1. The cool luminosity and temperature imply the Vela Junior CCO is indeed colder than many other young neutron stars and probably has a high mass that triggered fast neutrino cooling.
↳ astro-ph.HEastro-ph.SRhep-phnucl-thMNRAS(2026)·0 citations
07
Thermodynamics of ideal spin fluids and pseudo-gauge ambiguity
Jay Armas🇳🇱 · Akash Jain🇬🇧
Conserved currents of relativistic spin fluids derived from microscopic models are known to violate local thermodynamic relations. We present a systematic analysis of pseudo-gauge improvements in ideal spin hydrodynamics and identify a family of pseudo-gauges where standard thermodynamic relations are satisfied. We quantify pseudo-gauge ambiguities in the spin equation of state and derive universal thermodynamic relations that apply to conserved currents in any pseudo-gauge. As an application, we extract the thermodynamic variables and equations of state for free Dirac fermions and scalar fields.
↳ hep-thhep-phnucl-th6 citations
08
Neutrino production mechanisms in strongly magnetized quark matter: Current status and open questions
Igor A. Shovkovy🇺🇸 · Ritesh Ghosh🇺🇸
We review the main neutrino emission mechanisms operating in dense quark matter under strong magnetic fields, with particular emphasis on conditions expected in the interiors of compact stars. We discuss the direct Urca and neutrino synchrotron processes in unpaired quark matter, incorporating the effects of Landau-level quantization. For the direct Urca process, the quantization of the electron energy spectrum plays a critical role, whereas quark quantization can often be neglected at sufficiently high baryon densities. The resulting field-dependent neutrino emissivity is anisotropic and exhibits an oscillatory behavior as a function of magnetic-field strength. We explore the implications of these effects for magnetar cooling and for possible anisotropic neutrino emission that could contribute to pulsar kicks. In addition, we review the $ν ν ˉ$ synchrotron emission process, which, although subdominant, provides valuable insights into the interplay between magnetic fields and weak interactions in dense quark matter. Overall, our analysis highlights the nontrivial influence of strong magnetic fields on neutrino production in magnetized quark cores, with potential consequences for the thermal and dynamical evolution of compact stars.
↳ hep-phastro-ph.HEnucl-thUniverse(2026)·1 citation
09
Elastic lepton-proton two-photon exchange scattering: An exact HB $χ$ PT analysis including hadronic effects at NNLO
Rakshanda Goswami🇮🇳 · Pulak Talukdar🇮🇳 · Bhoomika Das🇮🇳 · Udit Raha🇮🇳 · Fred Myhrer🇺🇸
We present an exact analytical evaluation of the two-photon exchange (TPE) correction to the elastic lepton-proton differential scattering cross section at low-energies within the framework of heavy-baryon chiral perturbation theory. Our analysis focuses on the kinematic regime relevant to the ongoing MUSE experiment, and we therefore restrict the intermediate states to the dominant elastic channel. All loop integrals are evaluated analytically without approximations. Radiative and chiral recoil contributions of the proton are included, retaining kinematical and dynamical TPE corrections to the cross section through next-to-next-to-leading order [i.e., $O (α / M^{2})$ ] accuracy in the recoil expansion where $M$ is the proton mass. At this chiral order, pion-loop contributions demonstrate that structure-dependent TPE effects arise through the proton form factors. Our analytical results for the scattering cross section reveal non-vanishing residual proton structure effects of $O (α / M^{2})$ , despite substantial cancellations between TPE box and crossed-box contributions. Such effects were entirely absent at this accuracy in our earlier analysis based on the soft-photon approximation. Although the next-to-leading-order contributions are numerically sizable, the next-to-next-to-leading-order TPE corrections are found to be small, thereby indicating that the chiral expansion exhibits reasonably good perturbative convergence.
↳ hep-phnucl-th0 citations
10
Benchmarking neutrino-nucleus quasielastic scattering model predictions against a missing energy profile obtained using a monoenergetic neutrino beam
Jake McKean🇬🇧 · Laura Munteanu🇨🇭 · Seisho Abe🇯🇵
We examine three exclusive nuclear ground state shell models implemented in the NEUT neutrino event generator and benchmark them against the recent JSNS $^{2}$ measurement of missing energy using a monoenergetic neutrino source. The nature of the measurement allows a detailed investigation of nuclear ground-state modeling using a neutrino source, and gives access to a direct measurement of the neutron spectral function in a $^{12}$ C nucleus. The NEUT intranuclear cascade and nuclear deexcitation \textsc{NucDeEx} are used to simulate inelastic final-state interactions and nuclear deexcitations respectively. We find that the spectral function (SF) models perform better than relativistic mean field models in modeling both the ground state and the tail of the missing energy distribution when the NEUT cascade and nuclear excitation channels are turned on. We also find that taking into account the missing energy threshold for single nucleon knockout interactions results in all nuclear models being accepted based on the obtained $p$ -values.
↳ hep-exhep-phnucl-thPRD(2026)·3 citations
11
Probing Late-Stage Hadronic Interactions at High Baryon Density via $K^{* 0}$ Production in the RHIC Beam Energy Scan Program
STAR Collaboration: B. E. Aboona · J. Adam · G. Agakishiev · I. Aggarwal · M. M. Aggarwal · Z. Ahammed · A. Aitbayev · I. Alekseev · E. Alpatov · A. K. Alshammri · A. Aparin · S. Aslam and 375 other authors
A precision measurement of the $K^{* 0}$ meson yield is reported in Au+Au collisions at $s_{N N} = 7.7, 11.5, 14.6, 19.6,$ and $27 GeV$ using the high-statistics data sample collected by the STAR experiment during the Beam Energy Scan II (BES-II) program at RHIC. The transeverse momentum ( $p_{T}$ )-integrated yield ratios $(K^{* 0} + K^{* 0}) / (K^{+} + K^{-})$ in central collisions show a suppression relative to peripheral collisions at the $(1.7 - 3.6) σ$ level, while a thermal model without final-stage rescattering overpredicts this ratio with a deviation of $(6.9 - 8.2) σ$ . These results indicate a loss of the measured $K^{* 0}$ signal in central collisions due to re-scattering of its hadronic decay products in the hadronic phase. The $p_{T}$ -integrated yield of charged kaons exhibits an approximate scaling with charged-particle multiplicity, independent of collision energy and system size. A similar trend is observed for the short-lived $K^{* 0}$ resonance, although significant deviations emerge at lower energies. At BES energies, the $K^{* 0} / K$ ratio shows stronger suppression than at the highest RHIC and LHC energies within a given multiplicity bin, particularly in central and mid-central collisions. This behavior is consistent with changes in the effective hadronic interaction cross section and is supported by transport model calculations, which indicate dominant meson-baryon interactions at lower energies and meson-meson interactions at higher energies.
↳ nucl-exhep-exhep-thnucl-thPLB(2026)·8 citations
12
Carroll hydrodynamics with spin
Ashish Shukla🇮🇳 · Rajeev Singh🇷🇴 · Pushkar Soni🇮🇳
We formulate Carroll hydrodynamics with the inclusion of a spin current. Our strategy relies on the fact that the $c \to 0$ limit of relativistic hydrodynamics yields the equations of Carroll hydrodynamics. Starting with the pre-ultralocal parametrization of the background geometry and the hydrodynamic degrees of freedom for a relativistic fluid endowed with a spin current, the $c \to 0$ limit produces Carroll hydrodynamics with spin. It is known that boost-invariant hydrodynamic models for ultrarelativistic fluids relevant for the physics of quark-gluon plasma, such as Bjorken and Gubser flow, are manifestations of Carroll hydrodynamics under appropriate geometric choices for the underlying Carrollian structure. In this work, we further this mapping between such boost-invariant models and Carroll hydrodynamics, now with the inclusion of a spin current.
↳ hep-thnucl-th3 citations
13
Combined constraints on dark photons from high-energy collisions, cosmology, and astrophysics
A. W. Romero Jorge🇩🇪 · L. Sagunski🇩🇪 · Guan-Wen Yuan🇮🇹 · T. Song🇩🇪 · E. Bratkovskaya🇩🇪
We investigate a dark sector coupled to the Standard Model (SM) through a kinetically mixed dark photon $U$ associated with a new $U (1)^{'}$ gauge symmetry. Kinetic mixing $ε$ induces an effective coupling to the electromagnetic current, while $U$ interacts with stable dark matter (DM) $χ$ via a dark gauge coupling $g_{χ}$ . Our analysis is based on the parton-hadron-string dynamics (PHSD) transport approach, extended to include dark photon production and decay into dileptons ( $U \to e^{+} e^{-}$ ). In PHSD, dark photons are produced in high-energy collisions through Dalitz decays of light mesons ( $π^{0}, η, η^{'}, ω$ ), Delta-resonances ( $Δ \to N U$ ), direct vector meson decays ( $ρ, ω, ϕ \to U$ ), kaon decays, and $q q ˉ \to U$ annihilation. Building on previous PHSD benchmarks against dilepton data, we extract upper limits on $ε^{2} (m_{U}, m_{χ}, α_{χ})$ in both the visible regime ( $m_{U} < 2 m_{χ}$ ), where $U \to e^{+} e^{-}$ dominates, and the invisible regime ( $m_{U} > 2 m_{χ}$ ), where $U \to χ χ ˉ$ is kinematically open. Cosmological and astrophysical constraints are incorporated in two complementary ways. First, we compute the velocity-dependent self-interaction cross section $σ / m_{χ}$ for Yukawa-mediated SIDM and confront it with bounds from dwarf galaxies, galaxy groups, and clusters. Second, we determine thermal relic target curves by computing the relic abundance and requiring $Ω_{DM} h^{2} ≃ 0.12$ , consistent with \textit{Planck} measurements of the cosmic microwave background. Combining PHSD limits on $ε^{2}$ with relic density and self-interaction requirements, we exclude regions of the $(m_{χ}, m_{U})$ plane for each DM realization (Dirac, Majorana, or complex scalar) and identify benchmark scenarios in which heavy-ion, cosmological, and astrophysical constraints are simultaneously satisfied.
↳ hep-phastro-ph.COnucl-thPRD(2026)·3 citations

Affiliations

first authorsco-authorsvia INSPIRE