Nuclear Theory·nucl-th

Wednesday·June 17, 2026

13 papers—6 primary·7 cross-listed

07
Are neutrinos Majorana? Fixed-target and high-energy astrophysical searches decide
Gabriela Barenboim🇪🇸 · Mauricio Bustamante🇩🇰 · Qinrui Liu🇨🇦
Determining whether the neutrino is a Dirac or Majorana fermion remains a fundamental open question. Conventional searches rely on neutrinoless double beta decay, but this electron-only channel suffers from blind spots. We propose a new, complementary probe to overcome this limitation. A heavy neutral lepton (HNL) triggers a high-energy shift in how the active neutrino flavors ( $ν_{e}$ , $ν_{μ}$ , $ν_{τ}$ ) mix -- but only if the neutrinos are Majorana. For GeV-scale HNLs, the upcoming beam-dump experiment SHiP can discover the HNL and measure how it mixes with the active flavors. Separately, the scattering of TeV--PeV astrophysical neutrinos can resolve the HNL, revealing a shift in the proportions of each flavor arriving at Earth that could be detected by neutrino telescopes, regardless of the unknown flavor composition at the astrophysical neutrino sources. Because this flavor shift is most sensitive to the muon and tau sectors, it bypasses the blind spots of neutrinoless double beta decay. A correlated signal at SHiP and next-generation neutrino telescopes would prove that neutrinos are Majorana; its absence would point to them being Dirac.
↳ hep-phastro-ph.HEhep-exhep-th+10 citations
08
Short-Range Correlations Between Partons in a Proton
Jen-Chieh Peng🇺🇸 · Krishna Rajagopal🇺🇸 · John Terry🇺🇸
A principal lesson from recreating droplets of quark-gluon plasma (QGP) in heavy ion collisions is that it is a strongly coupled liquid, not a plasma of partons. The energy density and pressure of quarks and gluons confined within a proton are comparable to those of QGP at or just above the QCD transition temperature. Given this similarity between protons and QGP, we propose that the investigation of correlations between nearby partons within a proton must be a central goal for the future Electron-Ion Collider (EIC). Here, we ask how EIC measurements can discern such short-range correlations (SRCs) of quark pairs. Doing so would characterize the strongly coupled interior of a proton, augmenting the one-parton-at-a-time understanding of protons via (generalized) parton distribution functions, and could at the same time yield a key ingredient for the microscopic understanding of the liquid nature of QGP. Motivated by the experiments that have been used to demonstrate the existence of SRCs between nucleon pairs within a nucleus, we propose using EIC observables involving measurements of a jet and a pion, together with the scattered electron, to seek and quantify the possible existence of SRCs between quark pairs within a nucleon. The pronounced isospin dependence observed in the dominance of $n p$ SRCs over $pp$ or $nn$ SRCs has played a central role in establishing the importance of SRCs among nucleons in nuclei. Analogously, the QCD attraction in the $u d$ diquark channel can make the $u d$ SRC stronger than the $uu$ and $dd$ SRCs, allowing a first observation of partonic SRCs.
↳ hep-phnucl-exnucl-th0 citations
09
Scaling of the Surface Free Energy as a Probe of the QCD Critical Region
Joseph I. Kapusta🇺🇸 · Mayank Singh🇺🇸 · Shensong Wan🇺🇸
The QCD phase diagram is expected to have a critical point that separates the crossover and first-order transition lines. A realistic model that incorporates phase boundary effects is essential for heavy ion simulations to isolate the experimental signatures of a critical point. We discuss how to construct such an equation of state, and study its critical behavior. The effect of the coefficient of surface energy on the size of the critical region is investigated. We found that with this construction and with the chosen background equation of state, the temperature must be within one percent of its critical value to observe the critical exponents. This makes it doubtful that the critical exponents can be measured in heavy ion collisions, though it may still be feasible to observe signatures of a first-order phase transition. The method presented here is general and can be utilized with any given equation of state to test the viability of observing critical exponents in experiments.
↳ hep-phnucl-th0 citations
10
Can a Slow and Strong Phase Transition in Neutron Stars Relieve Major Compact-Star Observation Tensions?
Chen Zhang🇨🇳
Recent anomalous compact-star observations challenge the conventional neutron-star interpretation in complementary ways: HESS J1731--347 and XTE J1814--338 favor unusually small radii at low mass, while the secondary component of GW190814 appears too massive for an ordinary neutron star under GW170817-based maximum-mass inferences. We examine whether neutron stars with a strong first-order hadron--quark phase transition can address these tensions via the extended stable hybrid branches that arise when the phase conversion is slow compared to radial oscillations, while remaining consistent with GW170817 and NICER constraints. Using a piecewise-polytropic (PP) benchmark, supplemented by an independent speed-of-sound (CS) parametrization comparison, we find two viable patterns in a general parameter scan over both the hadronic and hybrid branches. Scenario 1 realizes an all-at-once solution: the same EOS has a pure hadronic branch compatible with both the GW190814-scale mass and HESS J1731--347, while its slow stable hybrid branch reaches XTE J1814--338. Scenario 2 retains the GW190814-scale hadronic branch but reaches XTE J1814--338 and HESS J1731--347 on slow stable branches in different transition-strength regimes.
↳ astro-ph.HEgr-qchep-phnucl-th2 citations
11
Quantum decoherence of hyperon spin correlations in QCD hadronization
Feng Liu🇺🇸 · Zhoudunming Tu🇺🇸
Hadronization, the transition of quarks and gluons into hadrons, lies beyond the reach of perturbative quantum chromodynamics (QCD) and is commonly described by the semiclassical Lund string model. Yet this very success raises a fundamental question: where does the quantumness go during hadronization? In this Letter, we propose an approach inspired by quantum information science, in which (i) quark-antiquark pairs excited from the QCD vacuum inherit its quantum numbers, giving rise to spin entanglement at their creation, and (ii) subsequent string breaking generates environmental degrees of freedom that induce quantum decoherence of the spin state. This framework simultaneously describes the $Λ$ hyperon spin-correlation data measured at RHIC [Nature 650, 65-71 (2026)] and at the LHC, establishing a quantitative connection between the QCD vacuum, spin entanglement and decoherence, and hadronization.
↳ hep-phhep-exnucl-exnucl-th3 citations
12
Hybrid Stars with Post-Merger Rotation Profiles
Kalin V. Staykov🇧🇬 · Violetta Sagun🇬🇧 · Lorenzo Cipriani🇮🇹 · Daniela D. Doneva🇪🇸 · Stoytcho S. Yazadjiev🇧🇬
We study the effect of differential rotation on hybrid stars with the first-order deconfinement phase transition from hadronic to color superconducting quark matter. The differential rotation is introduced within a realistic, four-parameter phenomenological rotation law, in which the maximum angular velocity of the rotating configuration is shifted away from the center. We focus on two classes of differentially rotating solutions, namely quasi-toroidal (type C) and quasi-spherical (type A), and study the changes in the star global properties and angular velocity profiles due to the presence of a phase transition. Thus, we demonstrate the existence of quasi-toroidal hybrid star configurations in which deconfined quark matter forms a ring around the center of mass, while hadronic matter remains at the center and outer layers. Furthermore, we show that when increasing the angular momentum $J$ the turning points of the $J = co n s t$ sequences shift towards lower energy densities, shrinking considerably the region where differentially rotating neutron stars with phase transitions exists. Interestingly, for both type A and type C solutions, the angular velocity profile is continuous throughout the star despite the discontinuity in the energy density. Moreover, we show that at the crossing points where the mass-radius curves for different equations of state intersect, the rotational profiles of the solutions are very close despite large differences in the energy density profiles. This reveals a possible degeneracy between the post-merger remnant properties for models with and without phase transitions, emphasizing the need for complementary multi-messenger observables to distinguish between them.
↳ gr-qcastro-ph.HEnucl-th0 citations
13
Observation of a dominant $0 f_{7/2}$ neutron configuration in the $^{32}$ Si $J^{π} = 5^{-}$ isomeric state
C. R. Hoffman · G. L. Wilson · J. Chen · B. P. Kay · T. L. Tang · S. R. Carmichael · M. Gott · S. Lesher · M. S. Martin · G. E. Morgan · J. Wu
An yrast, $J^{π} = 5^{-}$ , spin-trap isomer has been previously identified in $^{32}$ Si. The isomeric state decays predominantly via a hindered $E 3$ transition [B( $E 3$ ) = 0.0841(10)~W.u.], bypassing a nearby $E 2$ decay path to the first excited $3^{-}$ level. The single-neutron aspects of these negative parity levels were investigated via the $^{31}$ Si $(d$ , $p)^{32}$ Si reaction at 9.6~MeV/ $u$ using HELIOS and the ATLAS in-flight facility. The $5^{-}$ state appears as a dominant $ℓ = 3$ transfer with a relatively large spectroscopic factor, confirming its single-particle $ν 0 f_{7/2}$ character. The yrast $3^{-}$ level had a reduced $ℓ = 3$ spectroscopic factor of $\approx$ 0.44 compared to that of the $5_{1}^{-}$ level. This is similar to the situation observed in nearby $^{34}$ S which by contrast has a measured B( $E 2, 5^{-} \to 3^{-}$ ) transition strength closer to 1~W.u.. It has been concluded that the hinderance of the $5_{1}^{-} \to 3_{1}^{-}$ transition in $^{32}$ Si is not primarily due to the differing overlaps in the neutron structure. Instead, the lack of participation by both the protons and the neutrons in the transition is proposed as the transition-strength reduction mechanism.
↳ nucl-exnucl-thPRC(2026)·0 citations

Affiliations

first authorsco-authorsvia INSPIRE

Are neutrinos Majorana? Fixed-target and high-energy astrophysical searches decide

Short-Range Correlations Between Partons in a Proton

Scaling of the Surface Free Energy as a Probe of the QCD Critical Region

Can a Slow and Strong Phase Transition in Neutron Stars Relieve Major Compact-Star Observation Tensions?

Quantum decoherence of hyperon spin correlations in QCD hadronization

Hybrid Stars with Post-Merger Rotation Profiles

Observation of a dominant 0f7/2​ neutron configuration in the 32Si Jπ=5− isomeric state

Affiliations

Observation of a dominant $0 f_{7/2}$ neutron configuration in the $^{32}$ Si $J^{π} = 5^{-}$ isomeric state