The European Physical Journal C最新文献

An array of the kaon twist-two, three, four generalised transverse momentum dependent parton distributions (GTMDs) has been investigated within the framework of covariant and confining Dyson–Schwinger equations using contact interaction. GTMDs are of great significance as they encompass information regarding both the generalised parton distributions (GPDs) and the transverse momentum dependent parton distributions (TMDs), thus being considered as the parent distribution. From GTMDs, we can derive the twist-two, three, four GPDs and TMDs. GPDs are obtained through the integration of (varvec{k}_{perp }) from GTMDs, with a focus on the twist-two GPDs. The first Mellin moments of GPDs yield the form factors of local currents. The second Mellin moments of vector GPDs are related to gravitational form factors. The Wigner distribution can be obtained from a Fourier transform in the transverse space of the GTMDs at skewedness parameter (xi =0.) The Wigner distributions of an unpolarized, longitudinally polarized, and transversely polarized quark inside the kaon have been calculated. Through the three twist-two Wigner distributions, we study the dynamical spin effects of the quarks inside kaon to reveal its multidimensional structure. The spin-orbit correlations between a hadron and a quark can be explained based on the phase-space average of Wigner distributions. We investigate the correlation between the longitudinal spin and orbital angular momentum of valence quarks within the pion and kaon. Our findings reveal that (C_z^{u,K}=-0.336,) (C_z^{s,K}=0.242,) and (C_z^{u,pi }=-0.374.) The parton distribution function in impact parameter space can be derived from the Wigner distribution. The study focuses on the light-front transverse-spin distributions (rho _u^1left( varvec{b}_{bot },varvec{s}_{perp }right) ) and (rho _u^2left( varvec{b}_{bot },varvec{s}_{perp }right) ,) which exhibit distortions, and we calculate their average shift. This comprehensive analysis will enhance our understanding of the parton distribution picture of kaons. While there have been a few theoretical studies investigating the GTMDs in experiments, no experimental data is currently available. The results of our model calculation offer qualitative insights into these distributions.

The radio detection of very inclined air showers offers a promising avenue for studying ultra-high-energy cosmic rays (UHECRs) and neutrinos. Accurate reconstruction methods are essential for investigating the properties of primary particles. Recently, we developed an analytical (chi ^2) minimization method to reconstruct the electric field using three polarization components. The reconstruction yields no bias, with a 68% confidence interval of [(-)0.02, 0.02], and a standard deviation of 0.04 in the reconstruction of the peak envelope amplitude. In this paper, we perform a realistic reconstruction of the properties of primary particles using this reconstructed electric field. We employ a spherical wave model combined with an angular distribution function for arrival direction reconstruction, achieving an angular resolution of (0.04^circ ). We also present an energy reconstruction after accounting for the change in radio emission mechanisms in inclined air showers. We implement a new air-density correction factor, resulting in a 10% energy resolution. These results match the precision obtained when using simulated electric fields. These findings demonstrate the reliability and effectiveness of the recently developed electric field reconstruction methodology for its application on a typical event reconstruction chain. This ensures that the critical step of computing the electric field from the measure voltage at the antenna does not affect our ability to infer the properties of the primary particles, paving the way for future applications in radio experiments.

In this paper, we systematically investigate the optical appearance of a Schwarzschild black hole illuminated by three geometrically thin accretion disk models under varying observational inclination angles. Based on the geometric relationship between the black hole and observer, we first divide the accretion disk into co-side and counter-side semi-disks. We then analyze light ray trajectories, and calculate the total number of orbits and transfer functions for both semi-disks. The results reveal distinct inclination-dependence of lensed regions on different semi-disks: as inclination increases, the lensed region contracts for the counter-side semi-disk while expanding for the co-side one. Furthermore, through explicit specification of the emission profiles of the three models, we present optical images for both optically thin and thick disk scenarios at different inclinations. The results demonstrate that: (i) the bright rings in all three models become progressively compressed and deviate from circularity as inclination increases; (ii) for thick disks, partial rings are obscured and the overall intensity is lower than thin disks. These results may advance our understanding of general black hole imaging processes and provide a new approach to test gravitational theories through optical morphology studies.

In the third-generation (3G) gravitational-wave (GW) detector era, GW multi-messenger observations for binary neutron star merger events can exert significant effects on exploring the cosmic expansion history. Extending a previous work, we explore the potential of 3G GW standard siren observations in cosmological parameter estimation by considering their associated electromagnetic (EM) counterparts, including (gamma )-ray burst (GRB) coincidence observations by the Gravitational Wave High-energy Electromagnetic Counterpart All-sky Monitor and GW-triggered target-of-opportunity observations of kilonovae by different optical survey projects. During an assumed 10-year observation, we predict that the number of detectable GW-kilonova events is (sim 4900) with redshifts below (sim 0.4) under the GW detector network and Large Synoptic Survey Telescope in the i band, which is more than three times that of GW-GRB detections. For the cosmological analysis, we find that with the inclusion of GW-kilonova detections, the constraints on cosmological parameters from GW-EM detections are significantly improved compared to those from GW-GRB detections. In particular, GW-EM detections can tightly constrain the Hubble constant with precision ranging from (0.076%) to (0.034%). Moreover, GW multi-messenger observations can effectively break the cosmological parameter degeneracies generated by the typical EM observations, CMB+BAO+SN (CBS). The combination of CBS and GW-EM can tightly constrain the equation-of-state parameters of dark energy w in the wCDM model and (w_0) in the (w_0w_a)CDM model with precision of (0.72%) and (0.99%), respectively, meeting the standard of precision cosmology. In conclusion, GW multi-messenger observations could play a crucial role in helping solve the Hubble tension and probing the fundamental nature of dark energy.

We study the dynamics of particles near a charged back hole (BH) in the f(R, T) theory of gravity coupled with nonlinear electrodynamics and analyze how the parameters of the BH affect the motion of test particles. We discuss the stability of the circular orbits by employing the effective potential technique. We derive the mathematical expressions for the particle energy and its angular momentum as a function of the BH parameters and study them graphically. We also study the innermost stable circular orbits and the effective force acting on the test particles. The epicyclic oscillations of test particles are examined, and the analytical expressions for the radial frequency, the vertical frequency, and the orbital frequency are obtained. We also discuss the frequency of the periastron precession of particles. We show that the BH parameters have a significant impact on the particle dynamics. We observe that the effective potential increases with increasing charge and angular momentum, and the orbits are more unstable compared with the smaller values of these parameters: as the BH charge or the particle’s angular momentum increases, the particle experiences a greater effective force. However, it is not affected by the BH parameters a and b. We investigate the emission energy as a thermodynamic property of the BH and discuss the evaporation aspects of the BH.

We present results for threshold resummation of the invariant mass distribution, for on-shell production of a pair of W bosons at next-to-next-to-leading order + next-to-next-to-leading logarithmic(NNLO+NNLL) accuracy in QCD. Owing to its sensitivity to the self-interactions between gauge bosons, this process is important to investigate at the energies of the Large Hadron Collider(LHC). We achieve this resummation by exploiting the factorization properties of the soft and virtual parts of the partonic cross-section. Our analysis has been carried out for the invariant mass distribution up to Q = 2500 GeV. At this highest Q we find that, for 13.6 TeV LHC, the NNLL resummation enhances the NNLO cross-sections by about (6.3%) and reduces the conventional scale uncertainties from (6.8%) at NNLO to (4.1%) at NNLO+NNLL. We also estimate the intrinsic uncertainties due to the non-perturbative parton distribution functions at the highest perturbative order, for both fixed-order and resummed results, to be around (3%) for (Q sim ) 2000 GeV.

We explore a class of axion models where an accidental (textrm{U}(1)) Peccei-Quinn (PQ) symmetry automatically emerges from the interplay of vertical (grand-unified) and horizontal (flavor) gauge symmetries. We study a specific Pati-Salam realization in detail, and aim to generalize the conclusions. We show that our specific model offers protection from PQ-violating operators to high dimension, and demonstrate that the model can reproduce the Standard Model flavor structure. A distinctive feature of the vertical-horizontal setup is the presence of parametrically light fermions, known as anomalons, which are introduced to cancel the gauge anomalies of the flavor symmetry. We also identify a major challenge to building a fully realistic model, most notably that of Landau poles in gauge couplings before the Planck scale. For the specific model investigated, the pre-inflationary PQ-breaking scenario predicts the axion mass window to be (m_a in [2 times 10^{-8}, 10^{-3}],textrm{eV}). Conversely, a high-quality axion may be obtained instead in the post-inflationary scenario, with axion mass (m_a > rsim 0.01,textrm{eV}), and anomalon masses predicted below the (textrm{eV}) scale. We elaborate on anomalons’ cosmological production in the early universe, highlighting how measurements of (Delta N_textrm{eff}) could serve as a low-energy probe of the ultraviolet dynamics addressing the PQ quality problem.

We examine the dynamics of test particles and epicyclic frequencies around a charged regular black hole, investigating how its mass M and charge q influence orbital motion, stability, and high-energy phenomena. Using an effective potential approach, we derive analytical expressions for the specific energy and angular momentum of particles in stable circular orbits, demonstrating that increasing q shifts the innermost stable circular orbits (ISCOs) inward compared to the Schwarzschild black hole. We compute the radial, vertical, and orbital oscillation frequencies, revealing significant deviations from standard black hole predictions, particularly in the 3:2 frequency ratio associated with high-frequency. Through Markov Chain Monte Carlo (MCMC) analysis of observational data from X-ray binaries (including H 1743-322 and GRS 1915+105), we constrain the charge parameter to (q/M sim 0.3)–0.4 at high confidence levels. Further, we study particle collisions near the horizon, finding that centre-of-mass energies can be enhanced by up to 40% for (q approx 0.6M), indicating observable signatures in high-energy astrophysical processes. Our results provide testable predictions for distinguishing charged regular black holes from classical singular black holes. This work establishes a framework for probing black hole structures in the strong-gravity regime, with implications for fundamental physics and quantum gravity.

The static spherical vacuum solution in a bumblebee gravity model where the bumblebee field (B_mu ) has a one-component time-like vacuum expectation value (b_mu ) is studied. We show that in general curved space-time solutions are not allowed and only the Minkowski space-time exists. However, it is surprising that two non-trivial solutions can be obtained so long as a unique condition for the vacuum expectation (b^2equiv -b^mu b_mu =2/kappa ), where (kappa =8pi G), is satisfied. One of the solutions contains a naked singularity, while the other exhibits features analogous to a confining potential. We argue that naturally these solutions are not stable since quantum corrections would invalidate the likely numerical coincidence, unless there are some unknown fine-tuning mechanisms preventing any deviation from this condition. Nevertheless, the naked singularities and the photon sphere of these novel but peculiar solutions are discussed, and we show that the extremal Reissner-Nordström solution is a limit of one of our solutions.