The European Physical Journal C最新文献

We propose a unified framework for dark matter and dark energy based on the thermodynamic properties of a degenerate, relativistic Fermi gas in a higher-dimensional space-time. Extending the standard equation of state to D-dimensional space-time, we derive analytical expressions for the energy density, pressure, number density, sound velocity, and polytropic indices of a zero-temperature Fermi gas. Remarkably, we show that in the limit of vanishing Fermi momentum, the system exhibits a negative vacuum pressure and positive energy density when (D=(5+4n)), with (nin mathbb {N}). This feature provides a natural mechanism for the emergence of a cosmological constant-like component from fermionic matter in extra dimensions. In this context, dark matter arises from the bulk fermions’ rest mass energy, while dark energy emerges from their vacuum contributions. The observed cosmological vacuum energy density can be matched by fixing the compactification length scale, leading to constraints that depend on the fermion mass and the number of extra dimensions. Our results suggest that the dark sector may originate from a common fermionic source embedded in a higher-dimensional space-time, offering a novel pathway toward the unification of dark matter and dark energy.

Can models that are degenerate in electromagnetic observations (i.e., having identical shadows) be distinguished by their dynamical behaviors and quantum radiation properties? To address this question, this paper considers a unique charged black hole with logarithmic term corrections in NED (Mazharimousavi in Phys Lett B 841:137948, 2023, https://doi.org/10.1016/j.physletb.2023.137948, arXiv:2305.01048 [gr-qc]). It is found that for models degenerate with the shadow of a Schwarzschild black hole, although the oscillation frequencies (real parts) of their quasinormal modes (QNMs) are almost indistinguishable, their decay rates (imaginary parts) exhibit significant sensitivity. This provides the primary criterion for breaking the observational degeneracy. Furthermore, to investigate the effect of parameters, it is observed that when the parameter (zeta ) is fixed, the deviation behavior of QNM frequencies from those of the Schwarzschild black hole follows a more distinct pattern: the oscillation frequency decreases almost linearly with the increase in charge q, while the decay rate shows a stronger nonlinear dependence. In addition, the analysis of greybody factors (GFs) offers a second approach for distinction. It reveals a more complex non-monotonic behavior: in the low-frequency region, the transmittance of the Schwarzschild black hole is higher; however, above a cross frequency, the transmittance of the NED model rapidly surpasses that of the former. These results indicate that the damping time of QNMs and the precise shape of the Hawking radiation spectrum, rather than the shadow size, are more sensitive physical observables for detecting such logarithmic corrections. This study provides specific and distinguishable theoretical criteria for testing and constraining such NED models using gravitational wave astronomy and high-precision radiation observations in the future.

In the framework of a spherically symmetric Friedmann–Lemaître–Robertson–Walker (FLRW) spacetime, we construct a quintessence model driven by a nonlinear, massless spinor field in an open-universe scenario. The model parameters are constrained using recent cosmological observations, including the distance modulus from type Ia supernovae (binned Pantheon sample), Hubble parameter measurements from cosmic chronometers (CC) and the Sloan Digital Sky Survey (SDSS), and baryon acoustic oscillation (BAO) data. A comprehensive Markov chain Monte Carlo (MCMC) analysis yields best-fit estimates for a relatively lower present-day Hubble constant, and the equation-of-state parameter. The best-fit theoretical predictions are compared with observational data for both the Hubble parameter and the distance modulus. Furthermore, the deceleration parameter and the statefinder pair ({r, s}) are evaluated to demonstrate the model’s effectiveness in describing the universe’s late-time acceleration. The resulting lower value of (H_{0}=66.9~text {km},text {s}^{-1},text {Mpc}^{-1}) is consistent with the Planck cosmic microwave background (CMB) measurements and suggests a possible route toward alleviating the current Hubble tension. Overall, the spinor field quintessence model with (w_{textrm{de}}=-0.814) and (Omega _{m0} = 0.264) emerges as a statistically viable and physically consistent alternative to the standard (Lambda )CDM cosmology and conventional scalar-field quintessence frameworks.

We analyze the potential of rare charm decays as probes of new physics at a high-luminosity flavor facility operating at the Z pole, such as the FCC-ee or CEPC. In particular, we identify clean null-test observables in (D^0 rightarrow pi ^+ pi ^- nu bar{nu }) and in polarized (varLambda _c^+ rightarrow p ell ^+ ell ^-) decays with (ell =e, mu ). Complementarity with the LHC and HL-LHC flavor programs arises from the characteristic features of a Tera-Z environment: the capability to study missing-energy modes and charm production with significant polarization. We improve the theoretical description of (D^0 rightarrow pi ^+ pi ^- nu bar{nu }) decays and work out the phenomenology of polarization-induced null-test observables in (varLambda _c^+ rightarrow p ell ^+ ell ^-) decays. In regions of dilepton mass near the (phi ) resonance, polarization asymmetries can reach (O(5 %)) for muons and (O(14 %)) for electrons times the (varLambda _c^+) polarization. We also point out synergies between the dineutrino and the dilepton modes using the SMEFT framework of heavy new physics. Using the IDEA detector concept at FCC-ee, we find in simulation studies that dineutrino branching fractions as low as (sim 2 times 10^{-7}) can be probed, which reaches well into the parameter space of new physics, and also allows for discrimination of lepton flavor structures. Furthermore, the measurement of asymmetries in (varLambda _c^+ rightarrow p mu ^+ mu ^-) at (O(1 %)) will be possible. Similar sensitivities are expected for dielectron final states, although robust predictions will require further dedicated studies.

This study applies the concept of a complexity factor, originally formulated for static spherically symmetric spacetimes, to a system containing a charged fluid. The analysis commences by formulating the Einstein field equations for the anisotropic fluid and subsequently evaluating two distinct mass functions. The scalar ({Y}_{TF}) is selected as the complexity factor under Herrera’s formalism due to the incorporation of the key factors for dynamical complexity, which are pressure anisotropy and energy density inhomogeneity. Furthermore, the field equations are solved by imposing several constraints, one of them being the requirement of vanishing complexity. Using two different expressions for the radial metric potential, we obtain two independent solutions. We then determine the unknowns in these models by applying the junction conditions with the Reissner–Nordström metric as the exterior spacetime. Multiple stellar candidates’ observational data is assumed to check the acceptability of the obtained solutions graphically. It is concluded that both the suggested models depict stable and physically viable fluid configurations. These findings ultimately show that how well the vanishing complexity requirement behave in achieving feasible charged anisotropic fluid solutions.

Quasinormal modes for bosonic (scalar, electromagnetic, and axial gravitational) and fermionic field perturbations, radiated from black holes that carry quantum gravitational corrections at third order in the curvature to the Schwarzschild solution, are scrutinized from the propagation of analog transonic sound waves across a de Laval nozzle. The thermodynamic variables, the nozzle geometry, the Mach number, and the thrust coefficient are computed as functions of the parameter driving the effective action for quantum gravity containing a dimension-six local operator beyond general relativity. The quasinormal modes for quantum gravitational corrected analog black holes are also determined for higher overtones, yielding a more precise description of the quantum-corrected ringdown process and the gravitational waveform way before the fundamental mode sets in.

We study the structure of neutron stars within the framework of minimal dilatonic gravity (MDG), a scalar–tensor theory related to Brans–Dicke gravity with ( omega = 0 ). Using three realistic unified equations of state (EOSs), LOCV1804, LOCV1811, and LOCV1815, enabling us to investigate the sensitivity of MDG predictions to the stiffness of dense matter, we analyze stellar configurations for different values of the dilaton field mass ( m_{Phi } ). Our results show that a dilaton halo forms around the neutron star, contributing significantly to the total mass. The halo mass fraction reaches 20–30% in neutron stars with masses greater than ( 2M_{odot } ), leading to total masses that exceed those predicted by General Relativity. These results are consistent with mass measurements from recent gravitational wave and NICER (Neutron Star Interior Composition Explorer) observations. We also find that smaller dilaton field masses yield more massive neutron star–halo systems. For high-density stars, the dilaton pressure becomes negative at the center and behaves like dark energy, modifying the radial profile of the dilaton field.

With the advancements in clock timing technology, increasingly smaller time differences can be distinguished. Therefore, it is critical to investigate the fractional frequency shift of clocks at different locations on Earth. In this paper, we study it systematically under the influence of a subtle lunar tidal potential based on a new method. Our calculations in the geocentric Fermi frame show that when two clocks are located at the same latitude, the longitude difference changes the fractional frequency shift between them. A similar phenomenon occurs when there is a difference in latitude between two clocks on the ground at the same longitude. Interestingly, when the Moon’s longitude changes, the phase and amplitude of the lunar tidal fractional frequency shift between two clocks with the same longitude difference will change, while the change in the Moon’s latitude only affects the amplitude of the fractional frequency shift of these two clocks. Our results provide useful information for the calibration and synchronization of clocks on Earth.

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.