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  • Generalized gravitational baryogenesis of well-known f(T,TG) and f(T,B) models
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-09-24
    Nadeem Azhar; Abdul Jawad; Shamaila Rani

    The baryogenesis presents the theoretical mechanism that describes the matter–antimatter asymmetry in the history of early universe. In this work, we investigate the gravitational baryogenesis phenomena in the frameworks of f(T,TG) (where T and TG are the torsion scalar and teleparallel equivalent to the Gauss–Bonnet term respectively) and f(T,B) (where B denotes the boundary term between torsion and

    更新日期:2020-10-21
  • Starobinsky inflation in emergent gravity
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-10-19
    İlim İrfan Çimdiker

    Inflation is the main paradigm for explaining the homogeneity and isotropy of the observed universe. In view of its agreement with the Planck CMB data, we studied in this work Starobinsky inflation in models of induced gravity. Induced gravity theories are attractive because they arise from matter loops and have the potential to qualify as natural.

    更新日期:2020-10-19
  • Computing the luminosity distance via optimal homotopy perturbation method
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-10-14
    Bo Yu; Zi-Hua Wang; De-Zi Liu; Tong-Jie Zhang

    We propose a new algorithm for computing the luminosity distance in the flat universe with a cosmological constant based on Shchigolev’s homotopy perturbation method, where the optimization idea is applied to prevent the arbitrariness of initial value choice in Shchigolev’s homotopy. Compared with the some existing numerical methods, the result of numerical simulation shows that our algorithm is a

    更新日期:2020-10-15
  • Perfect fluid filled universe in odd dimensional pure Lovelock gravity
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-10-13
    Sudan Hansraj; Nomfundo Gabuza

    It is well known that d=2N+1 dimensional pure Lovelock metrics do not describe bounded distributions neither do they admit nontrivial vacuum solutions. On this basis it has been variously claimed that matter fields should be nondynamical. However, from earlier work it has long been demonstrated fairly generally that 2N+1 pure Lovelock solutions are not kinematic. In this work we find perfect fluid

    更新日期:2020-10-13
  • The expansion of the universe in binary star systems
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-10-05
    Kazuhiro Agatsuma

    Can all binary star systems merge in infinite time by emitting gravitational waves? The answer is no. The orbital radius shrinks from the gravitational wave emission; simultaneously, the universe is expanding if the Hubble–Lemaître law is universal on all distance scales. Inside the gravitational bound state, the cosmic expansion becomes visible near the critical radius given by the equilibrium between

    更新日期:2020-10-13
  • Clouds of strings in 4D Einstein–Gauss–Bonnet black holes
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-10-05
    Dharm Veer Singh; Sushant G. Ghosh; Sunil D. Maharaj

    Recently there has been significant interest in regularizing, a D→4 limit, of EGB gravity, and the resulting regularized 4D EGB gravities have nontrivial gravitational dynamics — namely the 4D EGB gravity. We present an exact charged black hole solution to the 4D EGB gravity surrounded by clouds of string (CS) and also analyse their thermodynamic properties. Owing to the corrected black hole due to

    更新日期:2020-10-11
  • H0 ex machina: Vacuum metamorphosis and beyond H0
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-10-08
    Eleonora Di Valentino; Eric V. Linder; Alessandro Melchiorri

    We do not solve tensions with concordance cosmology; we do obtain H0≈74km/s/Mpc from CMB+BAO+SN data in our model, but that is not the point. Discrepancies in Hubble constant values obtained by various astrophysical probes should not be viewed in isolation. While one can resolve at least some of the differences through either an early time transition or late time transition in the expansion rate, these

    更新日期:2020-10-11
  • A Kaluza–Klein inspired Brans–Dicke gravity with dark matter and dark energy model
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-10-05
    Chakrit Pongkitivanichkul; Daris Samart; Nakorn Thongyoi; Nutthaphat Lunrasri

    We propose the Kaluza–Klein inspired Brans–Dicke gravity model containing possible existence of dark matter and dark energy. The massive scalar field coupled with gravity in 5 dimensional space–time can be reduced to 4 dimensional gravity along with the dilaton ϕ, gauge fields Aμ, and the tower of scalar fields ηn. Two additional gauge fields are introduced to form “Cosmic Triad” vector field scenario

    更新日期:2020-10-08
  • On cosmic acceleration in four-dimensional Einstein–Gauss–Bonnet gravity
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-09-30
    H. Mohseni Sadjadi

    We study the possibility that in the model introduced in Glavan and Lin (2020), the Gauss–Bonnet term alone gives rise to the cosmic acceleration and super-acceleration in four-dimensional FLRW space–time at the late time. We also discuss transitions from deceleration to acceleration and acceleration to super-acceleration. We show that the Gauss–Bonnet invariant can drive the acceleration in the low

    更新日期:2020-10-05
  • A new coupled three-form dark energy model and implications for the H0 tension
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-10-01
    Yan-Hong Yao; Xin-He Meng

    We propose a new coupled three-form dark energy model to relieve the Hubble tension in this paper. Firstly, by performing a dynamical analysis with the coupled three-form dark energy model, we obtain four fixed points, including a saddle point representing a radiation dominated Universe, a saddle point representing a matter dominated Universe, and two attractors representing two saturated de Sitter

    更新日期:2020-10-05
  • Scale-dependent slowly rotating black holes with flat horizon structure
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-09-21
    Ángel Rincón; Grigoris Panotopoulos

    We study slowly rotating four-dimensional black holes with flat horizon structure in scale-dependent gravity. First, we obtain the solution, and then we study thermodynamic properties as well as the invariants of the theory. The impact of the scale-dependent parameter is investigated in detail. We find that the scale-dependent solution exhibit a new singularity not present in the classical solution

    更新日期:2020-09-30
  • Deep+ wide lensing surveys can measure the dark matter halos of dwarf galaxies
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-09-29
    Alexie Leauthaud; Sukhdeep Singh; Yifei Luo; Felipe Ardila; Johnny P. Greco; Peter Capak; Jenny E. Greene; Lucio Mayer

    The advent of new deep+ wide photometric lensing surveys will open up the possibility of direct measurements of the dark matter halos of dwarf galaxies. The HSC wide survey will be the first with the statistical capability of measuring the lensing signal with high signal-to-noise at log(M∗)∼8. At this same mass scale, The Rubin Observatory LSST will have the most overall constraining power with a predicted

    更新日期:2020-09-30
  • Probing phenomenological emergent dark energy model in a Bianchi type-I spacetime with the recent observational data
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-09-16
    Shivani Sharma

    In this work, we investigate the recently introduced phenomenological emergent dark energy (PEDE) model and the anisotropic extension of PEDE (APEDE) via Bianchi type-I spacetime metric with the latest observational data involving both low and high redshift datasets as, Hubble, Cosmic Microwave Background (CMB), Baryon Acoustic Oscillations (BAO) and Pantheon. We perform Bayesian inference analysis

    更新日期:2020-09-29
  • Unified dark fluid and cosmic transit models in Brans–Dicke theory
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-09-24
    Sunil K. Tripathy; Sasmita Kumari Pradhan; Zashmir Naik; Dipanjali Behera; B. Mishra

    Some dark energy cosmological models are constructed in the framework of a generalised Brans–Dicke theory which contains a self interacting potential and a dynamical coupling parameter. The models are constructed in the background of an anisotropic metric. The dark sector of the universe is considered through a unified linear equation of state. The parameters of the unified dark fluid have been constrained

    更新日期:2020-09-29
  • Repulsive regions in Lemaître–Tolman–Bondi gravitational collapse
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-09-21
    Roberto Giambò; Orlando Luongo; Hernando Quevedo

    We show that in the inhomogeneous Lemaître–Tolman–Bondi space–time there are specific regions in which repulsive gravity exists. To find these regions, we use an invariant definition of repulsive gravity based upon the behavior of the curvature eigenvalues. In addition, we analyze the effects of repulsive gravity on the dynamics of the gravitational collapse. In particular, we investigate the collapse

    更新日期:2020-09-26
  • Effects of dark matter in red giants
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-09-24
    Sunny Clea; Arun Kenath; C. Sivaram; S.B. Gudennavar

    Dark matter (DM) which constitutes five-sixths of all matter is hypothesized to be a weakly interacting non-baryonic particle, created in the early stages of cosmic evolution. It can affect various cosmic structures in the Universe via gravitational interactions. The effect of DM in main sequence stars and stellar remnants like neutron stars and white dwarfs has already been studied. Red giant phase

    更新日期:2020-09-26
  • f(R) gravity phase space in the presence of thermal effects
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-09-25
    V.K. Oikonomou; F.P. Fronimos; N.Th. Chatzarakis

    In this paper, we shall consider f(R) gravity and its cosmological implications, when an extra matter term generated by thermal effects is added by hand in the Lagrangian. We formulate the equations of motion of the theory as a dynamical system, that can be treated as an autonomous one only for specific solutions for the Hubble rate, which are of cosmological interest. Particularly, we focus our analysis

    更新日期:2020-09-25
  • Phase transition and thermal fluctuations of quintessential Kerr–Newman–AdS black hole
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-09-23
    M. Sharif; Qanitah Ama-Tul-Mughani

    This paper is devoted to analyzing the critical phenomenon and phase transition of quintessential Kerr–Newman-anti-de Sitter black hole in the framework of Maxwell equal-area law. For this purpose, we first derive thermodynamic quantities such as Hawking temperature, entropy and angular momentum in the context of extended phase space. These quantities satisfy Smarr–Gibbs–Dehum relation in the presence

    更新日期:2020-09-24
  • Growth of matter density perturbations in 4D Einstein–Gauss–Bonnet gravity
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-09-18
    Zahra Haghani

    Recently, a novel Einstein–Gauss–Bonnet gravity in four dimensions has been introduced (Glavan and Lin, 2020). We will investigate cosmological consequences of this model in details. We will consider linear matter density perturbations and also estimate relevant modified gravity parameters. Specially we will concentrate on the growth rate of non-relativistic matter perturbations on top of FRW geometry

    更新日期:2020-09-21
  • GW170817-compatible constant-roll Einstein–Gauss–Bonnet inflation and non-Gaussianities
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-09-15
    S.D. Odintsov, V.K. Oikonomou, F.P. Fronimos, S.A. Venikoudis

    In this paper we investigate the inflationary phenomenology of an Einstein–Gauss–Bonnet theory compatible with the GW170817 event, by imposing the constant-roll evolution on the scalar field. We develop the constant-roll GW170817-compatible Einstein–Gauss–Bonnet formalism, and we calculate the slow-roll indices and the observational indices of inflation, for several models of interest. As we demonstrate

    更新日期:2020-09-15
  • Einstein–Maxwell-scalar black holes with massive and self-interacting scalar hair
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-09-05
    Pedro G.S. Fernandes

    Recently, spontaneous scalarization of charged black holes has attracted a great deal of attention and motivated several studies of Einstein–Maxwell-scalar models. These studies have, however, only considered a massless and non-self-interacting scalar field. In this work a more realistic treatment of the problem is considered by studying the effects of scalar field mass and self-interacting terms on

    更新日期:2020-09-05
  • Dynamics of magnetized particles around 4-D Einstein Gauss–Bonnet black hole
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-08-29
    Ahmadjon Abdujabbarov, Javlon Rayimbaev, Bobur Turimov, Farruh Atamurotov

    In this paper, we have investigated the dynamics of magnetized particles around 4-D Einstein Gauss–Bonnet black hole immersed in an external asymptotically uniform magnetic field. We have shown that the magnetic interaction parameter responsible for circular orbits decreases for negative values of the Gauss–Bonnet parameter α and the range where magnetized particle’s stable circular orbits are allowed

    更新日期:2020-08-29
  • Dynamics of particles around the time conformal quantum corrected Schwarzschild black hole
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-08-26
    Amir Sultan Khan, Farhad Ali

    In this paper, we explore the dynamics of neutral and charged particles in presence/absence of magnetic field around the quantum corrected-Schwarzschild black hole as well as the time conformal quantum corrected-Schwarzschild black hole. We investigate the conditions under which the particles move towards or away from the vicinity of black hole when they collide with other particles. We study the effective

    更新日期:2020-08-26
  • Holographic dark energy with non-minimal derivative coupling to gravity effects
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-08-24
    Chonticha Kritpetch, Candrasyah Muhammad, Burin Gumjudpai

    Non-minimal derivative coupling (NMDC) to gravity in flat FLRW universe is investigated in the scenario of holographic dark energy. Kinetic term is coupled to the Einstein tensor under potential V=(1∕2)m2ϕ2. The free kinetic term is allowed to be canonical and phantom. Gravitational constant is modified with the NMDC coupling. Holographic cutoff at Hubble horizon gives modification to dark energy density

    更新日期:2020-08-24
  • Constraining an exact Brans–Dicke gravity theory with recent observations
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-08-20
    Hassan Amirhashchi, Anil Kumar Yadav

    In this paper first we study Brans–Dicke equations with the cosmological constant to find an exact solution in the spatially flat Robertson–Walker metric. Then we use Observational Hubble data, the baryon acoustic oscillation distance ratio data as well as cosmic microwave background data from Planck to constrain parameters of the obtained Brans–Dicke model. To compare our results and find out the

    更新日期:2020-08-20
  • Extended metastable dark energy
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-08-20
    J.A.S. Lima, G.J.M. Zilioti, L.C.T. Brito

    The metastable dark energy scenario is revisited by assuming that the current false vacuum energy density is the remnant from a primeval inflationary stage. The zero temperature scalar field potential is here described by an even power series up to order six which depends on 3 free parameters: the mass of the scalar field (m), the dimensionless (λ) specifying the standard self-interaction term, and

    更新日期:2020-08-20
  • The Local Group as a test system for Modified Newtonian Dynamics
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-08-18
    David Benisty, Eduardo I. Guendelman

    The Local Group (LG) is an appropriate test system for Modified Newtonian Dynamics, since the acceleration of M31 galaxy is fully in the deep MOND regime a≪a0. We model the LG as a two body problem of M31 and the Milky Way (MW) galaxies. Extending previous studies, we also include the Cosmological Constant. The assumption that in the big bang the galaxies emerged from the same place and approach to

    更新日期:2020-08-18
  • Quantum thermodynamics in the interior of a Reissner–Nordström black-hole
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-08-18
    Juan Ignacio Musmarra, Mauricio Bellini

    We study the interior of a Reissner–Nordström Black-Hole (RNBH) using Relativistic Quantum Geometry, which was introduced in some previous works. We found discrete energy levels for a scalar field from a polynomial condition for the Heun Confluent functions expanded around the effective causal radius r∗. From the solutions it is obtained that the uncertainty principle is valid for each energy level

    更新日期:2020-08-18
  • Regular black holes with exotic topologies
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-08-18
    Gustavo Melgarejo, Ernesto Contreras, Pedro Bargueño

    In this work we show that spherically symmetric regular black holes with topologies other than S3 de Sitter cores cannot be excluded from Borde’s theorem. In particular, we prove that spacetime connectivity leads to an S3 core by discarding other allowed topologies, such as the orientable and non orientable S2 bundles over S1, for achronal slices. Finally, some conjectures regarding physical quantification

    更新日期:2020-08-18
  • Scaling relations for dark matter core density and radius from Chandra X-ray cluster sample
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-08-15
    Gopika K., Shantanu Desai

    A large number of studies have found that the dark matter surface density, given by the product of the dark matter core radius (rc) and core density (ρc) is approximately constant for a wide range of galaxy systems. However, there has been only one systematic study of this ansatz for galaxy clusters by Chan et al. (2015), who found that the surface density for clusters is not constant and ρc∼rc−1.46

    更新日期:2020-08-15
  • Scalar field unification of interacting viscous dark fluid from a geometrical scalar–tensor theory of gravity
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-08-14
    José Edgar Madriz Aguilar, A. Gil-Ocaranza, M. Montes, J. Zamarripa

    We investigate, in the framework of a recently introduced new class of invariant geometrical scalar–tensor theory of gravity, the possibility that a viscous dark fluid can be described in a unified manner by a single scalar field. Thus we developed a model in which both the metric tensor and the scalar field have geometrical origin. The scalar field is characterized by a non-canonical kinetic term

    更新日期:2020-08-14
  • Galactic center constraints on self-interacting sterile neutrinos from fermionic dark matter (“ino”) models
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-08-10
    R. Yunis, C.R. Argüelles, N.E. Mavromatos, A. Moliné, A. Krut, M. Carinci, J.A. Rueda, R. Ruffini

    The neutrino minimal standard model (νMSM) has been tightly constrained in the recent years, either from dark matter (DM) production or from X-ray and small-scale observations. However, current bounds on sterile neutrino DM can be significantly modified when considering a νMSM extension, in which the DM candidates interact via a massive (axial) vector field. In particular, standard production mechanisms

    更新日期:2020-08-10
  • Stability of thin shell wormhole in f(R) theory of gravity
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-08-07
    A. Eid

    Dynamics of thin-shell wormholes within the context of f(R)gravity by joining two identical copies of Reissner–Nordstrom–de Sitter manifold using the cut and paste approach is discussed. The stability of wormholes is analyzed through the radial perturbation about the static solution and the modified generalized Chaplygin gas equation of state (EoS). This formalism gives rise two specific different

    更新日期:2020-08-07
  • (In)stability of black holes in the 4D Einstein–Gauss–Bonnet and Einstein–Lovelock gravities
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-08-07
    R.A. Konoplya, A. Zhidenko

    A (3+1)-dimensional Einstein–Gauss–Bonnet effective description of gravity has been recently formulated as the D→4 limit of the higher dimensional field equations after the rescaling of the coupling constant. This approach has been recently extended to the four-dimensional Einstein–Lovelock gravity. Although validity of the regularization procedure has not been shown for the general case, but only

    更新日期:2020-08-07
  • Space–time waves from a collapsing universe with a gravitational attractor
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-08-06
    Jaime Mendoza Hernández, Mauricio Bellini, Claudia Moreno

    We study a collapsing system attracted by a spherically symmetric gravitational source, with an increasing mass, that generates back-reaction effects that are the source of space–time waves. As an example, we consider an exponential collapse and the space–time waves emitted during this collapse due to the back-reaction effects, originated by geometrical deformation driven by the increment of the gravitational

    更新日期:2020-08-06
  • Asymptotic non-flatness of an effective black hole model based on loop quantum gravity
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-08-02
    Mariam Bouhmadi-López, Suddhasattwa Brahma, Che-Yu Chen, Pisin Chen, Dong-han Yeom

    For any non-rotating effective quantum (uncharged) black hole model to be viable, its asymptotic structure of spacetime should reduce to that of a Schwarzschild black hole. After examining the asymptotic structure of quantum black holes proposed in Ashtekar et al., (2018), we find that the solution is actually not asymptotically flat. Departure from asymptotically flat spacetime is a direct consequence

    更新日期:2020-08-02
  • Quantum magnetic monopoles at the Planck era from unified spinor fields
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-07-29
    Mauricio Bellini

    I use Unified Spinor Fields (USF), to discuss the creation of magnetic monopoles during preinflation, as excitations of the quantum vacuum coming from a condensate of massive charged vector bosons. For a primordial universe with total energy Mp, and for magnetic monopoles created with a total Planck magnetic charge qM=qP=±e∕α and a total mass mM, it is obtained after quantisation of the action that

    更新日期:2020-07-29
  • The dark universe future and singularities: The account of thermal and quantum effects
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-07-28
    Shin’ichi Nojiri, Sergei D. Odintsov

    The knowledge of the universe future is of fundamental importance for any advanced civilization. We study the future of the singular dark universe where thermal effects due to the Hawking radiation on the apparent horizon of the FRW universe are taken in the consideration. It is shown that the dark universe which ends up as finite-time Type I and Type III singularity or the infinite-time Little Rip

    更新日期:2020-07-28
  • Radiating black holes in the novel 4D Einstein–Gauss–Bonnet gravity
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-07-21
    Sushant G. Ghosh, Sunil D. Maharaj

    Recently Glavan and Lin (2020) formulated a novel Einstein–Gauss–Bonnet gravity in which the Gauss–Bonnet coupling has been rescaled as α∕(D−4) and the 4D theory is defined as the limit D→4, which preserves the number degrees of freedom thereby free from the Ostrogradsky instability. We present exact spherically symmetric nonstatic null dust solutions in the novel 4D Einstein–Gauss–Bonnet gravity that

    更新日期:2020-07-21
  • Growth of non-linear structures and spherical collapse in the Galileon Ghost Condensate model
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-07-18
    Noemi Frusciante, Francesco Pace

    We present a detailed study of the collapse of a spherical matter overdensity and the non-linear growth of large scale structures in the Galileon ghost condensate (GGC) model. This model is an extension of the cubic covariant Galileon (G3) which includes a field derivative of type (∇μϕ∇μϕ)2 in the Lagrangian. We find that the cubic term activates the modifications in the main physical quantities whose

    更新日期:2020-07-18
  • Formalizing slow-roll inflation in scalar–tensor theories of gravitation
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-07-18
    Kemal Akın, A. Savaş Arapoǧlu, A. Emrah Yükselci

    The viability of slow-roll approximation is examined by considering the structure of phase spaces in scalar–tensor theories of gravitation and the analysis is exemplified with a nonminimally coupled scalar field to the spacetime curvature. The slow-roll field equations are obtained in the Jordan frame in two ways: first using the direct generalization of the slow-roll conditions in the minimal coupling

    更新日期:2020-07-18
  • Dark matter annihilation in ω Centauri: Astrophysical implications derived from the MWA radio data
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-07-16
    Arpan Kar, Biswarup Mukhopadhyaya, Steven Tingay, Ben McKinley, Marijke Haverkorn, Sam McSweeney, Natasha Hurley-Walker, Sourav Mitra, Tirthankar Roy Choudhury

    We present an analysis of Murchison Widefield Array radio telescope data from ω Cen, possibly a stripped dwarf spheroidal galaxy core captured by our Galaxy. Recent interpretations of Fermi-LAT γ-ray data by Brown et al. (2019) and Reynoso-Cordova et al. (2019) suggest that ω Cen may contain significant Dark Matter. We utilize their best-fit Dark Matter annihilation models, and an estimate of the magnetic

    更新日期:2020-07-16
  • On (non-)dynamical dark energy
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-07-15
    Winfried Zimdahl, Júlio C. Fabris, Hermano Velten, Ramón Herrera

    The current Universe is composed by a mixture of relativistic species, baryonic matter, dark matter and dark energy which evolve in a non-trivial way at perturbative level. An advanced description of the cosmological dynamics should include non-standard features beyond the simplistic approach idealized by the standard cosmology in which cosmic components do not interact, are adiabatic and dissipationless

    更新日期:2020-07-15
  • Cosmology in theories with derivative matter coupling
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-07-14
    Zahra Haghani, Shahab Shahidi

    A class of modified gravity theories with higher order derivative terms of a function of the matter Lagrangian f(Lm) is considered. We will consider the Newtonian limit of the theory and show that the model predicts the standard Poisson equation for a massive test particle due to the higher order nature of the derivative matter coupling. Generally the energy–momentum tensor is not conserved, leading

    更新日期:2020-07-14
  • The central cusps in dark matter halos: Fact or fiction?
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-07-12
    A.N. Baushev, S.V. Pilipenko

    We investigate the reliability of standard N-body simulations by modeling of the well-known Hernquist halo with the help of GADGET-2 code (which uses the tree algorithm to calculate the gravitational force) and ph4 code (which uses the direct summation). Comparing the results, we find that the core formation in the halo center (which is conventionally considered as the first sign of numerical effects

    更新日期:2020-07-12
  • A solution to the initial condition problems of inflation: NATON
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-07-09
    Seokcheon Lee

    The recent astonishing realization of the negative absolute temperature (NAT) for motional degrees of freedom (Braun et al., 2013) inspires its possible application to the early universe. The existence of the upper bound on the energy of the system is the sufficient requirement for a NAT and this might correspond to the Planck scale at the Big Bang model. It has been argued that standard inflation

    更新日期:2020-07-09
  • Can massive neutrinos be responsible for late time phase transition aˆ la deceleration to acceleration in our Universe?
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-07-06
    M. Sami, Shynaray Myrzakul, Mudhahir Al Ajmi

    We attempt a novel mechanism to understand the underlying cause of late-time cosmic acceleration using a distinguished physical process taking place in the late Universe. In our opinion, the turning of massive neutrinos from relativistic to non-relativistic might cause a phase transition at late times. We implement this idea using massless λϕ4 theory coupled to massive neutrino matter such that the

    更新日期:2020-07-06
  • On bubble collisions in strongly supercooled phase transitions
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-07-04
    Marek Lewicki, Ville Vaskonen

    We study strongly supercooled cosmological phase transitions. We perform numerical lattice simulations of two-bubble collisions and demonstrate that, depending on the scalar potential, in the collision the field can either bounce to a false vacuum or remain oscillating around the true vacuum. We study if these cases can be distinguished from their gravitational wave signals and discuss the possibility

    更新日期:2020-07-04
  • Interacting dark energy in the early 2020s: A promising solution to the H0 and cosmic shear tensions
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-07-04
    Eleonora Di Valentino, Alessandro Melchiorri, Olga Mena, Sunny Vagnozzi

    We examine interactions between dark matter and dark energy in light of the latest cosmological observations, focusing on a specific model with coupling proportional to the dark energy density. Our data includes Cosmic Microwave Background (CMB) measurements from the Planck 2018 legacy data release, late-time measurements of the expansion history from Baryon Acoustic Oscillations (BAO) and Supernovae

    更新日期:2020-07-04
  • Effects of dark energy anisotropic stress on the matter power spectrum
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-07-03
    Gabriela Garcia-Arroyo, Jorge L. Cervantes-Cota, Ulises Nucamendi, Alejandro Aviles

    We study the effects of dark energy (DE) anisotropic stress on features of the matter power spectrum (PS). We employ the Parametrized Post-Friedmannian (PPF) formalism to emulate an effective DE, and model its anisotropic stress properties through a two-parameter equation that governs its overall amplitude (g0) and transition scale (cg). For the background cosmology, we consider different equations

    更新日期:2020-07-03
  • Large scales space–time waves from inflation with time dependent cosmological parameter
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-07-03
    Juan Ignacio Musmarra, Mauricio Bellini

    We study the emission of large-scales wavelength space–time waves during the inflationary expansion of the universe, produced by back-reaction effects. As an example, we study an inflationary model with variable time scale, where the scale factor of the universe grows as a power of time. The coarse-grained field to describe space–time waves is defined by using the Levy distribution, on the wavenumber

    更新日期:2020-07-03
  • Response to a comment on Dessert et al. “The dark matter interpretation of the 3.5 keV line is inconsistent with blank-sky observations”
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-07-03
    Christopher Dessert, Nicholas L. Rodd, Benjamin R. Safdi

    The dark matter explanation of the 3.5 keV line is strongly disfavored by our work in Dessert et al. (2020). Boyarsky et al. (2004) questions that conclusion: modeling additional background lines is claimed to weaken the limit sufficiently to re-allow a dark matter interpretation. We respond as follows. (1) A more conservative limit is obtained by modeling additional lines; this point appeared in its

    更新日期:2020-07-03
  • The spin tensor of dark matter and the Hubble parameter tension
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-07-02
    Fernando Izaurieta, Samuel Lepe, Omar Valdivia

    Allowing for a nonvanishing spin tensor for cold dark matter (ωDM=0) has the consequence of giving rise to an effective FLRW dynamics with a small negative barotropic constant for an effective dark matter density (−1∕3<ωeff≤0). This turns out to solve the Hubble parameter tension in a straightforward way.

    更新日期:2020-07-02
  • Anti-de Sitter Hayward black holes in Einstein–Gauss–Bonnet gravity
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-07-02
    Sushant G. Ghosh, Arun Kumar, Dharm Veer Singh

    Lovelock gravitation theory is a natural extension of the General Relativity to higher dimensions with the inclusion of only second-order terms correspond to the Einstein–Gauss–Bonnet gravity. In this paper, we find an exact Hayward black hole solution of D≥5-dimensional spacetime for Einstein–Gauss–Bonnet (EGB) gravity with negative cosmological constant (Λ) minimally coupled to non-linear electrodynamics

    更新日期:2020-07-02
  • f(Q,T) gravity models with observational constraints
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-07-02
    Simran Arora, S.K.J. Pacif, Snehasish Bhattacharjee, P.K. Sahoo

    The paper presents late time cosmology in f(Q,T) gravity where the dark energy is purely geometric in nature. We start by employing a well motivated f(Q,T) gravity model, f(Q,T)=mQn+bT where m,n and b are model parameters. Additionally we also assume the universe to be dominated by pressure-less matter which yields a power law type scale factor of the form a(t)=c2(At+c1)1A, where A=3(8π+b)n(16π+3b)

    更新日期:2020-07-02
  • Limits on stellar structures in Lovelock theories of gravity
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-07-01
    Sumanta Chakraborty, Naresh Dadhich

    We study the bound on the compactness of a stellar object in pure Lovelock theories of arbitrary order in arbitrary spacetime dimensions, involving electromagnetic field. The bound we derive for a generic pure Lovelock theory, reproduces the known results in four dimensional Einstein gravity. Both the case of a charged shell and that of a charge sphere demonstrates that for a given spacetime dimension

    更新日期:2020-07-01
  • Charged particle and epicyclic motions around 4D Einstein–Gauss–Bonnet black hole immersed in an external magnetic field
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-06-27
    Sanjar Shaymatov, Jaroslav Vrba, Daniele Malafarina, Bobomurat Ahmedov, Zdeněk Stuchlík

    We investigate particle motion in the vicinity of a 4D Einstein–Gauss–Bonnet (EGB) black hole immersed in external asymptotically uniform magnetic field. It is well known that magnetic fields can strongly affect charged particle motion in the black hole vicinity due to the Lorenz force. We find that the presence of the Gauss–Bonnet (GB) coupling gives rise to a similar effect, reducing the radius of

    更新日期:2020-06-27
  • Bardeen stellar structures with Karmarkar condition
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-06-27
    G. Mustafa, M. Farasat Shamir, Mushtaq Ahmad

    This current study is focussed to discuss the existence of a new family of compact star solutions by adopting the Karmarkar condition in the background of Bardeen black hole geometry. For this purpose, we consider static spherically symmetric spacetime with anisotropic fluid distribution in the presence of electric charge. We consider a specific model of grr metric function, to describe a new family

    更新日期:2020-06-27
  • Semiclassical analysis of the Starobinsky inflationary model
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-06-27
    Truman Tapia, Muhammad Zahid Mughal, Clara Rojas

    In this work we study the scalar power spectrum and the spectral index for the Starobinsky inflationary model using the phase integral method up-to third-order of approximation. We show that the semiclassical methods reproduce the scalar power spectrum for the Starobinsky model with a good accuracy, and the value of the spectral index compares favourably with observations. Also, we compare the results

    更新日期:2020-06-27
  • The general relativistic double polytrope for anisotropic matter
    Phys. Dark Universe (IF 4.473) Pub Date : 2020-06-27
    G. Abellán, E. Fuenmayor, E. Contreras, L. Herrera

    A general formalism recently proposed to study Newtonian polytropes for anisotropic fluids (Abellán et al., 2020) is here extended to the relativistic regime. Thus, it is assumed that a polytropic equation of state is satisfied by, both, the radial and the trangential pressures of the fluid. Doing so the generalized Lane–Emden equations are obtained and solved. Some specific models are obtained, and

    更新日期:2020-06-27
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