Physics

In this work, we propose a non-interacting model of Barrow holographic dark energy (BHDE) using Barrow entropy in a spatially flat FLRW Universe considering the IR cutoff as the Hubble horizon. We study the evolutionary history of important cosmological parameters, in particular, EoS ( ω B ) , deceleration parameter and, the BHDE and matter density parameter and also observe satisfactory behaviours in the BHDE the model. In addition, to describe the accelerated expansion of the Universe the correspondence of the BHDE model with the quintessence scalar field has been reconstructed.

The article communicates exploration of gravitational baryogenesis in presence of f(Q,T) gravity where Q denote the nonmetricity and T the trace of the energy momentum tensor. We study various baryogenesis interactions proportional to Q ˙ and Q ˙ f Q for the f(Q,T) gravity model f(Q,T)=α Q n+1 +βT , where α , β and n are model parameters. Additionally we report the viable parameter spaces for which an observationally consistent baryon-to-entropy can be generated. Our results indicate that f(Q,T) gravity can contribute significantly and consistently to the phenomenon of gravitational baryognesis.

Exploiting a topological soliton on a hypersphere, we construct baryon charge profile functions by calculating explicit isoscalar and isovector electric charge densities. In this approach we depict the charge density profiles for proton and neutron plotted versus hypersphere third angle μ . We next investigate the topologies of the hypersphere soliton via the Möbius strips which are related with the tubular neighborhoods of the half-twist circles inside the manifold S 3 . In particular, we show that in the hypersphere soliton the baryons are delineated in terms of the knot structure of the Möbius strips. We find that the knot structure of the Möbius strip type half-twist circles inside the nucleons can explain the gluon effect and confinement problem of the quark related model such as QCD.

6D spacetime with SO(3,3) symmetry is utilized to efficiently encode three generations of matter. A graviGUT model is generalized to a class of models that all contain three generations and Higgs boson candidates. Pati-Salam, SU(5) , and SO(10) grand unified theories are found when a single generation is isolated. For example, a SO(4,2) spacetime group may be used for conformal symmetry, Ad S 5 →d S 4 , or simply broken to SO(3,1) of Minkowski space. Another class of models finds SO(2,2) and can give Ad S 3 .

In this work, we evaluate the performance of a bidirectional teleportation protocol on an IBM-Q's quantum processor of six or more qubits. If the experiment is successful, we will implement this protocol between two submerged nuclear submarines on opposite sides of the ocean thanks to a satellite that generates and distributes entangled pairs, as well as transmits optical bits of disambiguation between both submarines.

The present article is devoted to constrain the model parameter χ for the f(R,T)=R+χT gravity model by employing the constraints coming from big bang nucleosynthesis. We solve the field equations and constrain χ in the range −0.14 κ 2 ≤χ≤0.84 κ 2 (where κ 2 = 8πG c 4 ) from the primordial abundances of light elements such as helium-4, deuterium and lithium-7. We found the abundances of helium-4 and deuterium agrees with theoretical predictions, however the lithium problem persists for the f(R,T) gravity model. We also investigate the evolution of entropy for the constrained parameter space of χ for the radiation and dust universe. We report that entropy is constant when χ=0 for the radiation dominated universe, whereas for the dust universe, entropy increases with time. We finally use the constraints to show that χ has negligible influence on the cold dark matter annihilation cross section.

We study the Horizon Wave Function (HWF) description of a generalized uncertainty principle (GUP) black hole in the presence of two natural cutoffs as a minimal length and a maximal momentum. This is motivated by a metric which allows the existence of sub-Planckian black holes, where the black hole mass m is replaced by M=m(1+ β 2 2 M 2 pl m 2 −β M pl m ) . Considering a wave-packet with a Gaussian profile, we evaluate the HWF and the probability that the source might be a (quantum) black hole. By decreasing the free parameter the general form of probability distribution, P BH , is preserved , but this resulted in reducing the probability for the particle to be a black hole accordingly. The probability for the particle to be a black hole grows when the mass is increasing slowly for larger positive β , and for a minimum mass value it reaches to 0 . In effect, for larger β the magnitude of M and r H increases, matching with our intuition that either the particle ought to be more localized or more massive to be a black hole. The scenario undergoes a change for some values of β significantly, where there is a minimum in P BH , so this expresses that every particle can have some probability of decaying to a black hole. In addition, for sufficiently large β we find that every particle could be fundamentally a quantum black hole.

In this paper we present a new black hole solution surrounded by dark matter halo in the galactic center using the mass model of M87 and that coming from the Universal Rotation Curve (URC) dark matter profile representing family of spiral galaxies. In both cases the DM halo density is cored with a size r 0 and a central density ρ 0 : ρ(r)= ρ 0 /(1+r/ r 0 )(1+(r/ r 0 ) 2 ) . Since r 0 ρ 0 =120 M ⊙ /pc 2 [Donato et al., MNRAS, 397, 1169, 2009], then by varying the central density one can reproduce the DM profile in any spiral. Using the Newman-Jains method we extend our solution to obtain a rotating black hole surrounded by dark matter halo. We find that, the apparent shape of the shadow beside the black hole spin a , it also depends on the central density of the surrounded dark matter ρ 0 . As a specific example we consider the galaxy M87, with a central density ρ 0 =6.9× 10 6 M ⊙ /kpc 3 and a core radius r 0 =91.2 kpc. In the case of M87, our analyses show that the effect of dark matter on the size of the black hole shadow is almost negligible compared to the shadow size of the Kerr vacuum solution hence the angular diameter 42 μ as remains almost unaltered when the dark matter is considered. For a small totally dark matter dominated spiral such as UGC 7232, we find similar effect of dark matter on the shadow images compared to the M87. However, in specific conditions having a core radius comparable to the black hole mass and dark matter with very high density, we show that the shadow images decreases compared to the Kerr vacuum black hole. The effect of dark matter on the apparent shadow shape can shed some light in future observations as an indirect way to detect dark matter using the shadow images.

This paper is devoted in the study of the hydrostatic equilibrium of stellar structure in the framework of modified f(R,T) gravity theory that allows the non-conservation of energy-momentum, with possible implications for several cosmological and astrophysical issues such as the late-time cosmic acceleration of the universe without appealing to exotic matter fields. For this purpose, we consider the gravitational Lagrangian by taking an arbitrary function of the Ricci scalar and the trace of the stress-energy tensor. We obtain a generic form for the gravitational field equations and derive the field equation for f(R,T) = R+2χT . Here we propose a particular metric potential \textit{Buchdahl ansatz} [Phys. Rev. D 116, 1027 (1959)] in principle, of explaining almost all the known analytic solutions to the spherically symmetric, static Einstein equations with a perfect fluid source. For the choice of f(T)=2χT one may observe that the pressure and energy density profiles are markedly different. Important cases, which have been analyzed in detail, are all possible Buchdahl solutions for spherical equilibrium configuration in f(R,T) gravity and compare them with standard gravity theory. We find that Buchdahl's solution in Einstein gravity and f(R,T) gravity behaves in a similar manner but in some situations Einstein gravity displays more pleasing behavior than its f(R,T) counterpart.

In this note we present an example from undergraduate quantum mechanics designed to highlight the versatility of the Dirac δ -function. Namely, we compute the expectation value of the Hamiltonian of a free-particle in a state described by a triangular wave function ψ(x) . Since the first derivative of ψ(x) is piecewise constant, and because this Hamiltonian is proportional to the second order spatial derivative, students often end up finding the expectation value to be zero --an unphysical answer. This problem provides a pedagogical application of the Dirac δ -function. By arriving at the same result via alternate pathways, this exercise reinforces students' confidence in the Dirac δ -function and highlights its efficiency and elegance.