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Journal of Physics G: Nuclear and Particle Physics - latest papers
Latest articles for Journal of Physics G: Nuclear and Particle Physics
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Production of vacuum particles from relativistic scalar particles in a deformed spacetime
In this work, we investigate the quantum dynamics of relativistic scalar particles in a (1+1)-dimensional de Sitter spacetime deformed by rainbow gravity, in which the spacetime metric depends explicitly on the energy of the probing particles. We begin by deriving the covariant Klein–Gordon equation in this modified gravitational background and obtain its exact solutions by two independent methods, in terms of Whittaker and Hankel functions. Building upon this formulation, we analyze the corresponding energy spectrum and the semiclassical solutions, and subsequently examine vacuum particle production within the Bogoliubov approach. Both sets of solutions lead to the same particle number density, which takes the form of a thermal Bose–Einstein distribution depending only on the temporal rainbow function . In the large-mass limit, it reduces to a Boltzmann factor characterized by an effective Gibbons–Hawking temperature , showing that rainbow gravity rescales the de Sitter horizon temperature and can either enhance or suppress particle creation relative to general relativity.
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Form-factor-constrained non-factorized transition-GPD tomography of N → Δ ( ...
A form-factor-constrained non-factorized transition-GPD reconstruction is developed for the electromagnetic transition. The production input consists of the published CLAS magnetic multipole amplitude and electric and scalar/Coulomb quadrupole ratios. Additional external low- ratio data are retained only as a separate ratio-sector diagnostic. The electroproduction quantities are propagated replica by replica and converted to the dimensionless Jones–Scadron transition form factors , , and . AICc model selection yields a modified dipole for , a dipole for , and a cubic expansion for . These fits define the imposed positive- normalization for factorized, correlated exponential, Regge-like, and double-distribution-inspired transition-GPD profiles. The upper boundary of the impact-parameter transform is fixed by the largest measured absolute-form-factor point, , so that no high- continuation beyond the measured range enters the production reconstruction. The primary transverse localization observable is therefore defined from the small- slope of the modeled transition GPD, with finite-window radial moments retained only as secondary core-shape diagnostics. For the slope-defined width, the transition form factor contributes an -independent channel-dependent offset, while the entire dependence is fixed by the chosen longitudinal–transverse profile ansatz. The factorized profile is -independent and the three non-factorized families generate distinct modeled dependences. The resulting reconstruction separates measured transition-form-factor information from model-dependent longitudinal structure and provides a controlled framework for assessing structural and covariance sensitivity in transition tomography.
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Clock–WEP tests of string-derived dilaton and modulus sectors
String compactifications and runaway-dilaton models can contain light scalar directions. Motion along these directions changes gauge couplings, the QCD scale, quark masses, and Yukawa parameters. A given string-derived sector then predicts low-energy slopes. Its gauge kinetic functions, matter-metric or Yukawa slopes, source charge, scalar trajectory, and scalar range determine a Damour–Donoghue weak-equivalence-principle (WEP) vector and a clock-drift vector. The analysis uses this map to compare such sectors with WEP and clock data. The numerical fit assumes one effective long-range scalar, or an aligned direction in a multi-field space. With that assumption, WEP tests and secular clock drifts probe related projections of the same scalar-slope vector. The minimal two-charge Damour–Donoghue fit uses Ti–Pt MICROSCOPE, Be–Ti torsion-balance, and Rb– Rb atom-interferometer data, then adds the Yb / secular -drift row. The WEP-only fit gives and , with correlation . The clock input is . It matches the WEP marginal reach when , with . For the benchmark and , this gives . This value marks equal information between the clock row and the WEP marginal constraint. A model becomes testable after it supplies , the scalar amplitude, and . As an example, the Damour–Piazza–Veneziano runaway-dilaton estimate lies near for order-unity parameters, well above the MICROSCOPE-level WEP scale. In the representative-isotope two-charge model, a MICROSCOPE-level Be–Ti-like row would reduce the long WEP axis by a factor ; a repeated Ti–Pt-like row would barely change it. The calculation tests compactification-level predictions for string-derived dilaton or modulus sectors after the model supplies its low-energy data.
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Vector meson photoproduction on the nucleus and the extraction of the nuclear suppression factor using asymmetric beams
Nuclear suppression factors quantify the modification of particle production in nuclei relative to free protons and thus provide insight into the properties of nuclear matter and its constituent quarks and gluons. The cross-section for photoproduction of a vector meson on a nucleus is usually determined in nucleus–nucleus collisions, which introduces a two-fold ambiguity because either nucleus can emit the photon. This can be resolved in asymmetric proton–nucleus collisions, where the ratio of photoproduction cross-sections on the proton and nucleus directly measures the nuclear suppression factor with minimal model dependence. Using simulated data corresponding to that already collected at the LHC, it is shown that the nuclear suppression factor can be measured with a statistical precision of 10% using mesons and a few percent using mesons. These results demonstrate the potential of proton-lead collisions to provide precise measurements of nuclear suppression factors and motivate future proton-lead running at the LHC.
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The sigma meson ( f 0 ...
We study the temperature dependence of meson screening masses in two-flavour lattice QCD using dynamical truncated overlap fermions (TOFs), a type of lattice chiral fermions. The screening masses for the , , , , and the sigma mesons are extracted by computing spatial correlation functions. This exploratory study uses meson screening masses and the connected/disconnected decomposition of the scalar correlator as diagnostic observables to examine how the disconnected contribution changes across the pseudocritical region. Above the pseudocritical temperature , the and screening masses become degenerate, consistent with chiral restoration. The pair also shows the expected degeneracy. Decomposition of the propagator reveals that the connected contribution dominates above , while the disconnected part becomes significant below , explaining the reduced statistical clarity observed at low . These results demonstrate that dynamical TOF simulations can capture the qualitative thermal behaviour of the scalar sector.