The European Physical Journal C最新文献

In the context of a homogeneous and isotropic universe, we consider the degeneracy condition at the background level between two scenarios in which processes out of equilibrium are possible; this consideration allows us to deviate from the perfect fluid description, and in this case bulk viscosity represents a viable candidate to describe entirely such effects. The cosmological model describing an unstable dark matter sector is mapped into a slight modification of the (Lambda )CDM model characterized by a viscous dark matter sector; under this consideration our description does not depend on a specific formulation of viscous effects and these can be fully reconstructed and characterized by the parameter that determines the decay ratio of dark matter. However, in this new scenario the cosmic expansion is influenced by the viscous pressure and the dark energy sector given by the cosmological constant is translated into a dynamical one. As a consequence of our formulation, the test against observations of the model indicates consistency with quintessence dark energy, but the crossing of the phantom divide can be accessible.

The Muon Collider is one of the most promising future collider facilities with the potential to reach multi-TeV center-of-mass energy and high luminosity. Due to the significant Higgs boson production cross section in muon-antimuon collisions at such high energies, the collider offers an excellent opportunity for in-depth exploration of Higgs boson properties. It holds the capability to significantly advance our understanding of the Higgs sector to a very high level of precision. However, the presence of beam-induced background resulting from the decay of the beam muons poses unique challenges for detector development and event reconstruction. In this paper, the prospects for measuring various Higgs boson properties at a center-of-mass energy of 3 TeV are presented, using a detailed detector simulation in a realistic environment. The study demonstrates the feasibility of achieving high precision results with the current state-of-the-art detector design. In addition, the paper discusses the detector requirements necessary to achieve this level of accuracy.

We studied two different models that included Lorentz Invariance Violation coupling in the scattering processes of (e^+e^- rightarrow mu ^+mu ^-). We found that using the model with the dual electromagnetic tensor (tilde{F}_{mu nu }) resulted in violations of unitarity in both vector and axial scenarios. On the other hand, using the model with nonminimal coupling with (F_{mu nu }) preserved unitarity in both vector and axial cases. As a result, this could have significant implications, given that the nonminimal coupling model with the dual electromagnetic tensor (tilde{F}_{mu nu }) appeared to be potentially superior to the electromagnetic tensor (F_{mu nu }). Therefore, we believe that these findings could provide a valuable guide for further exploration into the study of CPT and Lorentz breaking phenomena, with significant implications that are certainly nontrivial.

In the last three decades, numerical stochastic perturbation theory (NSPT) has proven to be an excellent tool for calculating perturbative expansions in theories such as Lattice QCD, for which standard, diagrammatic perturbation theory is known to be cumbersome. Despite the significant success of this stochastic method and the improvements made in recent years, NSPT apparently cannot be successfully implemented in low-dimensional models due to the emergence of huge statistical fluctuations: as the perturbative order gets higher, the signal to noise ratio is simply not good enough. This does not come as a surprise, but on very general grounds, one would expect that the larger the number of degrees of freedom, the less severe the fluctuations will be. By simulating 2D O(N) non-linear sigma models for different values of N, we show that indeed the fluctuations are tamed in the large N limit, meeting our expectations: for a large number of internal degrees of freedom (i.e. for large enough N), NSPT perturbative computation can be pushed to large perturbative orders n. By re-expressing our perturbative expansions as power series in the gN (’t Hooft) coupling, we show some evidence that at any given order n there is a tendency to gaussianity for the stochastic process distributions at large N. By summing our series, we can verify leading order results for the energy and its (field theoretic) variance in the large N limit. We finally establish general relationships between the various perturbative orders in the expansion of the (field theoretic) variance of a given observable and combinations of variances and covariances of given orders NSPT stochastic processes. Having established all this, we conclude discussing interesting applications of NSPT computations in the context of theories similar to O(N) (i.e. (CP(N-1)) models).

In this paper, we introduce the (phi )CDM model, and we compare to the concordance model. We provide their epoch evolution, we perform a dynamical analysis to each model, and a comparative analysis between the two models. We revitalise these two models, since we study them in systems with higher number of variables. Furthermore, the (phi )CDM model is more complete than the one that we found in the literature, since we take into account all the so far discovered epochs, radiation, matter, and dark energy epochs. In contrast in the literature there is no study including the radiation epoch for this model. We find that both models can describe the generally accepted scenario of cosmic evolution, and current observations. Both models, describe qualitative and quantitative current observations about the epoch behaviour of the species of the universe. We find the (phi )CDM model has the following exotic transition from a dominant radiation energy density ratio epoch and a low dominant matter energy density ratio and high dominant radiation energy density ratio epoch, towards a dominant scalar potential energy density ratio epoch, in the matter-potential-scalar plane.

In the Einstein–Gauss–Bonnet (EGB) gravity models, the slow-roll approximation has been extended by taking into account the first-order slow-roll parameter (delta _1 =-2,H^2,xi ^prime /U_0), which is proportional to the first derivative of the Gauss–Bonnet coupling function (xi ) with respect to the e-folding number. These extensions lead to the question of the accuracy of effective potential reconstruction during the generalization of attractors in EGB gravity. We have reconstructed models using the extended slow-roll approximations and compared them with the exact expressions and the standard slow-roll approximation.

In this study, we explore the pre-inflationary dynamics of the universe using a non-commutative extension of the mLQC-I framework. By incorporating a scalar field potential, we show that key features of Loop Quantum Cosmology (LQC), such as the quantum bounce and the super-inflationary phase, are preserved. Numerical solutions to the modified Hamiltonian equations, with initial conditions set at the quantum bounce, reveal that the universe’s early expansion rate is sensitive to the shape of the potential. For a chaotic potential, the inclusion of non-commutativity results in a faster expansion rate, whereas for the Starobinsky potential, the expansion rate decreases with increasing non-commutative parameter (theta ). Additionally, higher values of (theta ) lead to an increased time derivative of the Hubble parameter, causing a shorter yet more expansive super-inflationary phase. Over time, Hubble parameters for different values of (theta ) converge. For the Starobinsky potential, the Hubble parameter consistently decreases with larger (theta ), resulting in a prolonged super-inflationary stage. The study also addresses the validation of the Hamiltonian constraint during the evolutionary time.

In order to unravel the composition of the isoscalar DN,  (D^*N,) (D_1N,) and (D_2^*N) molecular pentaquarks, we carry out a systematic investigation of their M1 and E1 radiative decays and magnetic moment properties. Using the constituent quark model and taking into account the S–D wave mixing effect and the coupled channel effect, our analysis yields numerical results indicating that the M1 and E1 radiative decays and the magnetic moment properties of these molecular pentaquarks provide some insights into their inner structures. These results can provide crucial clues for distinguishing their spin-parity quantum numbers and configurations in experimental studies. In addition, we highlight the importance of the electromagnetic properties as key observables for elucidating the inner structures of the observed (Lambda _c^{+} (2940)) and (Lambda _c^{+} (2910).) We hope that these findings can inspire our experimental colleagues to further explore the family of the single-charm molecular pentaquarks and to investigate the inner structures of the (Lambda _c^{+} (2940)) and (Lambda _c^{+} (2910)) in future studies.

In this paper, we exhaustively investigate the quasinormal modes (QNMs) of a probe scalar field over a d-dimensional regular black hole (BH) characterized by the parameter A. The quasinormal frequencies (QNFs) exhibit different behaviors with respect to the parameter A for (d=4) and (d>4). Firstly, the trends of QNFs with respect to A exhibit completely opposite patterns for the case of (d=4) and (d>4). Secondly, in the four-dimensional regular BH, a non-monotonic behavior with respect to A is observed in the imaginary part of the fundamental modes with vanishing angular quantum number. In contrast, for nonzero angular quantum number or (d>4), non-monotonic behavior is observed only in the overtones. Thirdly, an overtone outburst accompanied by an oscillatory patter is observed only in the case of (d>4), but not in (d=4).

Accurate characterization of quantum yield is crucial to the reconstruction of energy depositions in silicon at the eV scale. This work presents a new method for experimentally calculating quantum yield using vacuum UV-sensitive silicon photomultipliers (SiPMs), which can be used to determine the probabilities that a UV photon absorbed in a silicon crystal will produce one, two, or three electron–hole pairs. Results are presented which fully constrain the distribution at photon energies up to 7.75 eV. This method works by exploiting the saturation of photon detection efficiency which occurs when these devices are biased sufficiently high above their avalanche breakdown voltage. The measured quantum yield values are lower than those that have been previously reported by experimental data and modelling – this is expected to impact the sensitivity of experiments searching for light dark matter through direct detection in semiconductors, and should also be taken into account when characterizing the performance of UV photodetectors with high quantum efficiency. Measurements have been taken using a Hamamatsu VUV4 and an FBK VUV-HD3 device, showing good agreements between devices, and at a range of temperatures from 163–233 K. The validity of the method is assessed using supplementary measurements of absolute photon detection efficiency, and an additional novel method of measuring average quantum yield using DC current–voltage measurements of SiPMs is presented and used for corroboration.