Two photons from the ground state para-positronium annihilation are emitted in a maximally entangled singlet state of orthogonal polarizations. In case of the Compton scattering of both photons the phenomenon of quantum entanglement leads to a measurable increase in the azimuthal correlations of scattered photons, as opposed to a classical description treating the two scattering events as independent. The probability of the scattering of the system of entangled photons is described by the Pryce-Ward cross section dependent on a difference of the azimuthal scattering angles in the fixed coordinate frame, while the independent scattering of single photons is described by the Klein-Nishina cross section dependent on the azimuthal angle relative to each photon’s initial polarization. Since the singlet state of orthogonal polarizations is rotationally invariant, it does not carry any physical information on the initial polarizations of the single annihilation photons. In such bipartite state the angular origin for the Klein-Nishina cross section is undefined, making the Pryce-Ward and Klein-Nishina descriptions mutually exclusive. However, semi-classical simulations of the joint Compton scattering of entangled photons – implementing the Pryce-Ward cross section, but still treating the two photons as separate entities – can reconcile the Pryce-Ward correlations with the Klein-Nishina statistics for single photons by implementing a modified version of a scattering cross section presented in this work.

Croatia

Petar Žugec

Eric Andreas Vivoda

Mihael Makek

Ivica Friščić

A reconciliation of the Pryce-Ward and Klein-Nishina statistics for semi-classical simulations of annihilation photons correlations

In this work, we construct the <italic>D</italic>-wave isoscalar <math altimg='si1.svg'><mrow><mi>&#960;</mi><mi>&#960;</mi><mo linebreak='goodbreak'>/</mo><mi>K</mi><mover accent='true'><mi>K</mi><mo>&#175;</mo></mover></mrow></math> coupled-channel Omn&#232;s matrix, formulated to satisfy unitarity, analyticity, and the appropriate asymptotic behavior. We employ a two-channel <italic>K</italic>-matrix model containing poles associated with the <italic>f</italic> <inf>2</inf>(1270) and <math altimg='si7.svg'><mrow><msubsup><mi>f</mi><mrow><mn>2</mn></mrow><mo>&#8242;</mo></msubsup><mrow><mo>(</mo><mn>1525</mn><mo>)</mo></mrow></mrow></math> resonances. The resulting unitary scattering matrix, which reproduces the experimental <italic>&#960;&#960;</italic>&#8239;&#8594;&#8239; <italic>&#960;&#960;</italic> and <math altimg='si27.svg'><mrow><mi>&#960;</mi><mi>&#960;</mi><mo>&#8594;</mo><mi>K</mi><mover accent='true'><mi>K</mi><mo>&#175;</mo></mover></mrow></math> data and PDG information, serves as input to the homogeneous two-channel Muskhelishvili-Omn&#232;s equation. We compare our Omn&#232;s matrix with previous constructions based on <math altimg='si27.svg'><mrow><mi>&#960;</mi><mi>&#960;</mi><mo>&#8594;</mo><mi>K</mi><mover accent='true'><mi>K</mi><mo>&#175;</mo></mover></mrow></math> phases extracted from sums of Breit-Wigner amplitudes. The Omn&#232;s matrix developed here provides a reliable dispersive input for form-factor calculations and resonance studies in the tensor-meson sector. As an application, we show that it enables a simultaneous and accurate description of the BESIII <italic>J</italic>/ <italic>&#968;</italic>&#8239;&#8594;&#8239; <italic>&#960;</italic> 0 <italic>&#960;</italic> 0 <italic>&#947;</italic> and <italic>J</italic>/ <italic>&#968;</italic>&#8239;&#8594;&#8239; <italic>K<inf>S</inf>K<inf>S</inf>&#947;</italic> spectra in the <math altimg='si2.svg'><mrow><mi>J</mi><mo linebreak='goodbreak'>=</mo><mn>2</mn></mrow></math> electric-dipole (E1) partial wave.

Germany

Igor Danilkin

Oleksandra Deineka

United States

Spain

Emilie Passemar

Marc Vanderhaeghen

Coupled-channel Omnès matrix for the <italic>D</italic>-wave isoscalar <math altimg='si1.svg'><mrow><mi>&#960;</mi><mi>&#960;</mi><mo linebreak='goodbreak'>/</mo><mi>K</mi><mover accent='true'><mi>K</mi><mo>&#175;</mo></mover></mrow></math> system and its application to <italic>J</italic>/ <italic>&#968;</italic>&#8239;&#8594;&#8239; <italic>&#960;</italic> 0 <italic>&#960;</italic> 0 <italic>&#947;</italic>,&#8201; <italic>K<inf>S</inf>K<inf>S</inf>&#947;</italic>

We explore the cosmological consequences of a modified cosmology inspired by string T-duality. We incorporate the zero-point length correction, <italic>l</italic> <inf>0</inf>, into the gravitational potential and derive the modified Friedmann equations via thermodynamic approach at the apparent horizon of a Friedmann-Robertson-Walker (FRW) universe. The resulting framework introduces a dimensionless coupling parameter <math altimg='si63.svg'><mrow><mi>&#946;</mi><mo>&#8764;</mo><msubsup><mi>l</mi><mn>0</mn><mn>2</mn></msubsup><msubsup><mi>H</mi><mn>0</mn><mn>2</mn></msubsup></mrow></math> quantifying deviations from the standard &#923;CDM model. Using Bayesian inference with <small-caps>Cobaya</small-caps> and MCMC sampling, we constrain the model parameter against late-time observations, including PantheonPlus and Union3 Type Ia supernovae, cosmic chronometers, DESI DR2 BAO measurements, and Amati-calibrated GRBs. The joint analysis yields an upper bound <math altimg='si64.svg'><mrow><mi>&#946;</mi><mo>&#8818;</mo><mi mathvariant='script'>O</mi><mo>(</mo><msup><mn>10</mn><mrow><mo>&#8722;</mo><mn>3</mn></mrow></msup><mo>)</mo></mrow></math> (68% C.L.), implying that any deviation from the standard &#923;CDM scenario ( <math altimg='si65.svg'><mrow><mi>&#946;</mi><mo linebreak='goodbreak'>=</mo><mn>0</mn></mrow></math>) is extremely small within the current observational precision. Model comparison through the Akaike Information Criterion shows that the &#923;CDM and T-duality models provide statistically equivalent fits to the data, exhibiting only a marginal preference for &#923;CDM. These results provide the first quantitative observational constraints on the cosmological imprint of string T-duality-inspired modifications and underscore the potential of future high-precision surveys to test possible residual effects of such corrections in the late-time Universe.

G.G. Luciano

South Africa

Chile

A. Paliathanasis

Iran

A. Sheykhi

Observational constraints on the modified cosmology inspired by string T-duality

We derive a parameter-free geometric constraint on residue phases dictated by the pole-threshold angle. Using the <italic>N</italic>(2190) anomaly as a test case, this constraint reveals a sign ambiguity in prior data; correcting the sign ambiguity yields a phase of <math altimg='si13.svg'><mrow><mo>&#8722;</mo><msup><mn>28</mn><mo>&#8728;</mo></msup><mo>&#177;</mo><msup><mn>10</mn><mo>&#8728;</mo></msup></mrow></math>, matching our prediction. This consistency validates the method as a model-independent diagnostic for distinguishing compact from molecular states, offering a rigorous tool for exotic spectroscopy.

S. Ceci

Bosnia and Herzegovina

R. Omerović

H. Osmanović

M. Uroić

United Kingdom

M. Vukšić

B. Zauner

Geometric constraint on residue phases: resolving the <italic>N</italic>(2190) anomaly and implications for exotic states

Quantum information science has been broadly explored in Einstein gravity and in various modified gravity theories; however, its extension to quantum gravity settings remains largely unexplored. Motivated by this gap, in this paper we investigate the degradation of quantum entanglement of scalar and Dirac fields in the third-type black hole geometry arising from effective quantum gravity, which incorporates generic quantum gravitational corrections beyond classical general relativity. This quantum corrected spacetime is free of a Cauchy horizon and can be cast into a Rindler form in the near-horizon regime, allowing a direct identification of vacuum modes and a clear correspondence with the framework developed for uniformly accelerated observers. Within this framework, we compute the quantum entanglement and mutual information of uniformly entangled detector pairs in terms of the quantum parameter <math altimg='si6.svg'><mover accent='true'><mi>&#950;</mi><mo>&#732;</mo></mover></math>, the mode frequency <math altimg='si7.svg'><mover accent='true'><mi>&#969;</mi><mo>&#732;</mo></mover></math>, and Bob&#8217;s radial position <italic>R</italic> <inf>0</inf>. The quantum parameter <math altimg='si6.svg'><mover accent='true'><mi>&#950;</mi><mo>&#732;</mo></mover></math> consistently weakens the horizon-induced loss of correlations. For scalar fields this effect is pronounced, producing clear departures from the classical behavior, whereas for Dirac fields the familiar correlation pattern remains intact but its degradation is noticeably reduced. Overall, <math altimg='si6.svg'><mover accent='true'><mi>&#950;</mi><mo>&#732;</mo></mover></math> acts as a universal protective factor against gravitational suppression of quantum correlations. The third-type effective quantum black hole therefore provides a controlled and physically transparent arena for probing how quantum-gravity corrections influence relativistic quantum information.

China

Xiaobao Liu

Wentao Liu

Shu-Min Wu

Entanglement degradation of static black holes in effective quantum gravity

We investigate low-energy <italic>N&#981;</italic> scattering driven by a pole-enhanced triangle-like diagram, in which the two-Kaon-exchange contribution is promoted by the near-threshold &#923;(1405) pole in the <math altimg='si3.svg'><mrow><mi>N</mi><mover accent='true'><mi>K</mi><mo>&#175;</mo></mover></mrow></math> subsystem. Using an unphysical Kaon mass motivated by lattice simulations, we evaluate the <italic>N&#981;</italic> scattering length and find that this mechanism generates an attractive interaction with a magnitude of <math altimg='si7.svg'><mrow><mo>&#8722;</mo><mn>1.1</mn></mrow></math> to <math altimg='si8.svg'><mrow><mo>&#8722;</mo><mn>0.5</mn><mspace width='0.16em' /><mtext>fm</mtext></mrow></math>. Spin-dependent effects are not treated explicitly and are expected to provide subleading corrections in the near-threshold region. We further analyze the low-energy behavior of the triangle-like diagram amplitude and show that the scattering length depends on the parameter <italic>&#948;</italic>, defined as the mass difference between the <math altimg='si9.svg'><mrow><mi>K</mi><mover accent='true'><mi>K</mi><mo>&#175;</mo></mover></mrow></math> threshold and the <italic>&#981;</italic> meson, and the pole position of &#923;(1405), where the &#923;(1405) plays a crucial role to understand <italic>N&#981;</italic> interaction. Furthermore, by employing physical hadron masses, our calculated scattering length is found to be consistent with current experimental data, providing a unified description across both unphysical and physical mass regimes. This type of interaction differs from that associated with van der Waals-type forces or the long-range tail of two-pion exchange, highlighting the role of three-body dynamics encoded in the pole-enhanced triangle-like diagram in shaping the near-threshold <italic>N&#981;</italic> interaction.

Mao-Jun Yan

Chun-Sheng An

Cheng-Rong Deng

Low-energy <italic>N&#981;</italic> scattering from a pole-enhanced triangle diagram

In General Relativity, there exist two objects of limiting compactness, one with a null boundary defining the horizon of a black hole and the other with a timelike boundary defining a Buchdahl star. The two are characterized by gravitational energy equal to or half the mass. Since non-gravitational mass-energy is the source of gravitational energy, these configurations suggest an underlying energetic balance. In this letter, we demonstrate, in a simple and general manner, that the corresponding equilibrium state always represents a minima of an appropriate quasi-local energy functional, thereby establishing energetic (variational) stability within the quasi-local configuration space.

India

Soumya Chakrabarti

Chiranjeeb Singha

Naresh Dadhich

On the stability of the objects of limiting compactness: Black hole and Buchdahl star

We propose to investigate short-range correlations (SRCs) in nuclei by studying sub and near-threshold photoproduction of <italic>&#981;</italic>-meson. The feasibility of exploring this nuclear structure in electron-positron collision experiments such as Beijing Spectrometer III (BESIII) and Super <italic>&#964;</italic>-Charm Facility (STCF) was investigated by utilizing their beryllium-based ( 9Be) beam pipe. The cross sections for these processes as well as the likelihood of detection by BESIII and STCF are calculated. Due to the limited number of events, BESIII is inadequate for the proposed measurement, while the future STCF provides a higher probability of successfully measuring this process. These findings suggest that electron-positron collider could play a valuable role in elucidating the fundamental physics behind the nuclear modification of parton distribution functions. This proposed analysis of photon-nucleon interactions represents uncharted territory, promising fresh prospects for applications in both particle and nuclear physics.

Wei Wang

Ji Xu

Xing-Hua Yang

Ya-Teng Zhang

Shuai Zhao

Exploring nucleon structure through sub- and near-threshold <italic>&#981;</italic>-meson photoproduction

The neutron energy spectrum measured at the Earth’s surface shows three distinct peaks: a thermal energy peak, an evaporation peak between 2-3 MeV, and a cascade peak near 100 MeV. However, the spectrum measured at a depth of 1604 metres water equivalent reveals the absence of cascade peak. This indicates an effective shielding of cosmogenic component of neutron background by the rock overburden. A comprehensive analysis of measured neutron fluence data from various facilities, combined with simulation data, indicates that the radiogenic component is the primary source of neutron background at the underground laboratories even at a depth of 1000 metres water equivalent. The concentrations of uranium and thorium in the surrounding rock are identified as the major factors influencing this background.

Sujoy Chatterjee

K. Banerjee

S. Dawn

Arijit Sen

S. Manna

A.K. Bakshi

Pratap Roy

V.N. Jha

R. Datta

B.K. Sapra

Depth-dependent background neutron distribution at the deep underground laboratory

A nonzero neutrino magnetic moment arises already in the minimally extended Standard Model with right-handed massive Dirac neutrinos. The well-known consequence of the neutrino magnetic moment is the phenomenon of neutrino spin oscillations in a magnetic field. It can manifest itself not only as a lack in the flux of active cosmic neutrinos arriving on Earth but also as characteristic features in low-energy neutrino elastic scattering processes. Following our approach developed earlier, in this work we study the influence of arbitrary spin-flavor state of incoming neutrino on low-energy neutrino scattering off different particles in a detector. We demonstrate that superposition of left- and right-handed helicity neutrino states gives rise to an azimuthal asymmetry in the angular distribution of the recoil momenta. We present numerical calculations for elastic neutrino scattering on electrons, protons and 40Ar and 132Xe nuclei, demonstrating the azimuthal-asymmetry effect. Our results indicate the unique potential of directional neutrino detection to observe the neutrino spin oscillations.

Russia

Konstantin A. Kouzakov

Fedor M. Lazarev

Alexander I. Studenikin

The potential of directional neutrino detection to observe neutrino spin oscillations