**Stratospheric temperature anomalies as imprints from the dark Universe**

Publication date: Available online 14 February 2020Source: Physics of the Dark UniverseAuthor(s): K. Zioutas, A. Argiriou, H. Fischer, S. Hofmann, M. Maroudas, A. Pappa, Y.K. SemertzidisAbstractThe manifestation of the dark Universe begun with unexpected large-scale astronomical observations. Here we are investigating the possible origin of small-scale anomalies, like that of the annually observed temperature anomalies in the stratosphere (38.5 – 47.5 km). Unexpectedly within known physics, we observe a planetary relationship of the daily stratospheric temperature distribution. Interestingly, its spectral shape does ...

**Source: **Physics of the Dark Universe - February 16, 2020 **Category: **Physics **Source Type: **research

**Dynamical evidence of a dark solitonic core of 109M⊙ in the milky way**

Publication date: Available online 13 February 2020Source: Physics of the Dark UniverseAuthor(s): Ivan De Martino, Tom Broadhurst, S.-H. Henry Tye, Tzihong Chiueh, Hsi-Yu SchiveAbstractA wavelike solution for the non-relativistic universal dark matter (wave-DM) is rapidly gaining interest, following pioneering simulations of cosmic structure as an interference pattern of coherently oscillating bosons. A prominent solitonic standing wave is predicted at the center of every galaxy, representing the ground state solution of the coupled Schrödinger-Poisson equations, and it has been identified with the wide, kpc scale dar...

**Source: **Physics of the Dark Universe - February 14, 2020 **Category: **Physics **Source Type: **research

**Galaxy cluster hydrostatic masses using Tolman–Oppenheimer–Volkoff equation**

Publication date: Available online 13 February 2020Source: Physics of the Dark UniverseAuthor(s): Sajal Gupta, Shantanu DesaiAbstractMotivated by previous studies in literature about the potential importance of relativistic corrections to galaxy cluster hydrostatic masses, we calculate the masses of 12 relaxed clusters (with Chandra X-ray data) using the Tolman-Oppenheimer-Volkov (TOV) equation of hydrostatic equilibrium and the ideal gas equation of state. Analytical formulae for gas density and temperature profiles for these clusters, previously derived by Vikhlinin et al. (2006) were used to obtain these masses. We...

**Source: **Physics of the Dark Universe - February 14, 2020 **Category: **Physics **Source Type: **research

**Stability of self-gravitating anisotropic fluids in f(R,T) gravity**

Publication date: Available online 14 February 2020Source: Physics of the Dark UniverseAuthor(s): M.Z. Bhatti, Z. Yousaf, M. YousafAbstractThis manuscript aims to discuss the factors holding in/stability of axially symmetric compact system with anisotropic environment in the background of f(R,T) gravity, where R is invariant Ricci curvature and T stands for trace of energy momentum tensor. We constituted field and conservation equations in the background of f(R,T) gravity. To establish the collapse equation, we make use of perturbation for all the variables involving in conservation equations, field equations, extra curvat...

**Source: **Physics of the Dark Universe - February 14, 2020 **Category: **Physics **Source Type: **research

**Dark degeneracy I: Dynamical or interacting dark energy?**

Publication date: Available online 10 February 2020Source: Physics of the Dark UniverseAuthor(s): Rodrigo von Marttens, Lucas Lombriser, Martin Kunz, Valerio Marra, Luciano Casarini, Jailson AlcanizAbstractWe revisit the dark degeneracy that arises from the Einstein equations relating geometry to the total cosmic substratum but not resolving its individual components separately. We establish the explicit conditions for the dark degeneracy in the fluid description of the dark sector. At the background level, this degeneracy can be formally understood in terms of a unified dark sector Equation of State (EoS) that depends bot...

**Source: **Physics of the Dark Universe - February 11, 2020 **Category: **Physics **Source Type: **research

**A neutron star with a strange quark star-like mass-radius relation**

Publication date: Available online 7 February 2020Source: Physics of the Dark UniverseAuthor(s): A. Savaş Arapoğlu, A. Emrah YükselciAbstractWe study the structure of spherically symmetric and static objects in the presence of a nonminimally coupled scalar field having a potential of the form V(ϕ)=−μ2ϕ2∕2+λϕ4∕4. We numerically solve equations of the system using two different realistic equations of state for neutron matter and give the mass–radius relations as well as the radial profiles of the scalar field, densities and the mass function for a sample configuration. We show that a speci...

**Source: **Physics of the Dark Universe - February 8, 2020 **Category: **Physics **Source Type: **research

**Fuzzy Euclidean wormholes in the inflationary universe**

Publication date: Available online 5 February 2020Source: Physics of the Dark UniverseAuthor(s): Pisin Chen, Daeho Ro, Dong-han YeomAbstractIn this paper, we investigate complex-valued Euclidean wormholes in the Starobinsky inflation. Due to the properties of the concave inflaton potential, the classicality condition at both ends of the wormhole can be satisfied, as long as the initial condition of the inflaton field is such that it is located sufficiently close to the hilltop. We compare the probabilities of classicalized wormholes with the Hartle-Hawking compact instantons and conclude that the Euclidean wormholes are pr...

**Source: **Physics of the Dark Universe - February 7, 2020 **Category: **Physics **Source Type: **research

**Analysis method for detecting topological defect dark matter with a global magnetometer network**

Publication date: Available online 6 February 2020Source: Physics of the Dark UniverseAuthor(s): Hector Masia-Roig, Joseph A. Smiga, Dmitry Budker, Vincent Dumont, Zoran Grujic, Dongok Kim, Derek F. Jackson Kimball, Victor Lebedev, Madeline Monroy, Szymon Pustelny, Theo Scholtes, Perrin C. Segura, Yannis K. Semertzidis, Yun Chang Shin, Jason E. Stalnaker, Ibrahim Sulai, Antoine Weis, Arne WickenbrockAbstractThe Global Network of Optical Magnetometers for Exotic physics searches (GNOME) is a network of time-synchronized, geographically separated, optically pumped atomic magnetometers that is being used to search for correla...

**Source: **Physics of the Dark Universe - February 7, 2020 **Category: **Physics **Source Type: **research

**Joint analysis of EDGES 21-cm line observations with standard candles and rulers in ΛCDM and non-adiabatic gCg models**

Publication date: Available online 4 February 2020Source: Physics of the Dark UniverseAuthor(s): C. Pigozzo, S. Carneiro, J.C. FabrisAbstractA decomposed generalised Chaplygin gas (gCg) with energy flux from dark energy to dark matter, represented by a negative value for the gas parameter α, is shown to alleviate the tension between EDGES data and the cosmological standard model. Using EDGES data and employing a Bayesian statistical analysis, the agreement with the standard model is only marginal. However, if α is negative enough the gCg fits remarkably well the data, even in combination with SNe Ia datasets. O...

**Source: **Physics of the Dark Universe - February 5, 2020 **Category: **Physics **Source Type: **research

**On the change of old neutron star masses with galactocentric distance**

Publication date: Available online 30 January 2020Source: Physics of the Dark UniverseAuthor(s): Antonino Del Popolo, Maksym Deliyergiyev, Morgan Le Delliou, Laura Tolos, Fiorella BurgioAbstractWe show that the pulsar mass depends on the environment, and that it decreases going towards the center of the Milky Way. This is due to two combined effects, the capture and accumulation of self-interacting, non-annihilating dark matter by pulsars, and the increase of the dark matter density going towards the galactic center. We show that mass decrease depends both on the density profile of dark matter, steeper profiles producing a...

**Source: **Physics of the Dark Universe - January 31, 2020 **Category: **Physics **Source Type: **research

**A tight correlation between the enclosed gravitational mass and hot gas mass in galaxy clusters at intermediate radii**

Publication date: Available online 28 January 2020Source: Physics of the Dark UniverseAuthor(s): Man Ho ChanAbstractMany studies point out that there exists some tight correlations between dark matter and baryonic matter at different radii in galaxies. However, similar tight correlations can only be found in galaxy clusters for large radii. Here we report extremely tight correlations between the gravitational mass Mgrav and hot gas mass Mgas in galaxy clusters at the hot gas core radius rc and at 2rc (i.e. Mgrav(rc) vs Mgas(rc) and Mgrav(2rc) vs Mgas(2rc)). By using the X-ray data of 64 large galaxy clusters with different...

**Source: **Physics of the Dark Universe - January 30, 2020 **Category: **Physics **Source Type: **research

**Electromagnetic effects on polytropes in f(R) gravity**

Publication date: Available online 27 January 2020Source: Physics of the Dark UniverseAuthor(s): M.Z. Bhatti, Z. TariqAbstractThe center of attention of this article is to examine the dynamics of conformally flat anisotropic spheres in the background of electromagnetic field satisfying the polytropic equations of state. We have resorted to the general framework developed in Herrera and Barreto (2013) that helps to inspect the rudimentary attributes of polytropic spheres in the framework of a particular f(R) gravity. We explored physical constraints for couple of families of relativistic polytropes in this scenario. By maki...

**Source: **Physics of the Dark Universe - January 29, 2020 **Category: **Physics **Source Type: **research

**Higgs inflation in complex geometrical scalar-tensor theory of gravity**

Publication date: Available online 24 January 2020Source: Physics of the Dark UniverseAuthor(s): José Edgar Madriz Aguilar, J. Zamarripa, M. Montes, C. RomeroAbstractWe derive a Higgs inflationary model in the context of a complex geometrical scalar-tensor theory of gravity. In this model the Higgs inflaton scalar field has geometrical origin playing the role of the Weyl scalar field in the original non-riemannian background geometry. The energy scale enough to generate inflation from the Higgs energy scale is achieved due to the compatibility of the theory with its background complex Weyl-integrable geometry. We fo...

**Source: **Physics of the Dark Universe - January 25, 2020 **Category: **Physics **Source Type: **research

**What is the amplitude of the gravitational waves background expected in the Starobinsky model?**

Publication date: January 2020Source: Physics of the Dark Universe, Volume 27Author(s): Fabrizio Renzi, Mehdi Shokri, Alessandro MelchiorriAbstractThe inflationary model proposed by Starobinsky in 1979 predicts an amplitude of the spectrum of primordial gravitational waves, parametrized by the tensor to scalar ratio, of r=0.0037 in case of a scalar spectral index of nS=0.965. This amplitude is currently used as a target value in the design of future CMB experiments with the ultimate goal of measuring it at more than five standard deviations. Here we evaluate how stable are the predictions of the Starobinsky model on r cons...

**Source: **Physics of the Dark Universe - January 22, 2020 **Category: **Physics **Source Type: **research

**Stellar structures in f(G) gravity with Tolman–Kuchowicz spacetime**

Publication date: January 2020Source: Physics of the Dark Universe, Volume 27Author(s): M. Farasat Shamir, Tayyaba NazAbstractThis paper is devoted to explore some relativistic configurations of stellar objects for static spherically symmetric structures in the context of modified f(G) gravity, by exploiting the Tolman–Kuchowicz spacetime (Tolman, 1939; Kuchowicz, 1968). We develop the equations of motion for spherically symmetric spacetime in the presence of anisotropic matter distribution by considering the physically valid expressions of the metric potentials, ν=Br2+2lnC and λ=ln(1+ar2+br4). To attain th...

**Source: **Physics of the Dark Universe - January 21, 2020 **Category: **Physics **Source Type: **research

**End of the constant-roll inflation, and the reheating temperature**

Publication date: Available online 20 January 2020Source: Physics of the Dark UniverseAuthor(s): H. Mohseni Sadjadi, V. AnariAbstractBy extending the potential, we propose a mechanism for the end of the constant-roll inflation and the subsequent reheating phase in the FLRW space–time. Based on astrophysical data, we estimate the Universe reheating temperature. (Source: Physics of the Dark Universe)

**Source: **Physics of the Dark Universe - January 21, 2020 **Category: **Physics **Source Type: **research

**Gravitational waves from binary black holes as probes of the structure formation history**

Publication date: Available online 20 January 2020Source: Physics of the Dark UniverseAuthor(s): Tomohiro NakamaAbstractGravitational-wave detectors on earth have detected gravitational waves from merging compact objects in the local Universe. In future we will detect gravitational waves from higher-redshift sources, which trace the high-redshift structure formation history. That is, by observing high-redshift gravitational-wave events we will be able to probe structure formation history. This will provide additional insight into the early Universe when primordial fluctuations are generated and also into the nature of dark...

**Source: **Physics of the Dark Universe - January 21, 2020 **Category: **Physics **Source Type: **research

**Effect of dark energy on Hawking–Page transition**

Publication date: January 2020Source: Physics of the Dark Universe, Volume 27Author(s): Yao Wu, Wei XuAbstractIt is well known that there exists a Hawking–Page (HP) transition between Schwarzschild-AdS (SAdS) black hole and the thermal AdS vacuum. In this paper, we study a similar phase transition under the effect of dark energy, namely HP transition of AdS black hole surrounded by quintessence dark energy. It is shown that there always exists a HP transition between the quintessence AdS (qAdS) black hole and the thermal AdS vacuum. In contrast to Einstein gravity, we find that the high temperature phase can be domin...

**Source: **Physics of the Dark Universe - January 18, 2020 **Category: **Physics **Source Type: **research

**Stellar structures in f(G) gravity with Tolman-Kuchowicz spacetime**

Publication date: Available online 17 January 2020Source: Physics of the Dark UniverseAuthor(s): M. Farasat Shamir, Tayyaba NazAbstractThis paper is devoted to explore some relativistic configurations of stellar objects for static spherically symmetric structures in the context of modified f(G) gravity, by exploiting the Tolman-Kuchowicz spacetime (Tolman, 1939; Kuchowicz, 1968) [1]. We develop the equations of motion for spherically symmetric spacetime in the presence of anisotropic matter distribution by considering the physically valid expressions of the metric potentials, ν=Br2+2lnC and λ=ln(1+ar2+br4). ...

**Source: **Physics of the Dark Universe - January 17, 2020 **Category: **Physics **Source Type: **research

**Effect of dark energy on Hawking-Page transition**

Publication date: Available online 15 January 2020Source: Physics of the Dark UniverseAuthor(s): Yao Wu, Wei XuAbstractIt is well known that there exists a Hawking-Page (HP) transition between Schwarzschild-AdS (SAdS) black hole and the thermal AdS vacuum. In this paper, we study a similar phase transition under the effect of dark energy, namely HP transition of AdS black hole surrounded by quintessence dark energy. It is shown that there always exists a HP transition between the quintessence AdS (qAdS) black hole and the thermal AdS vacuum. In contrast to Einstein gravity, we find that the high temperature phase can be do...

**Source: **Physics of the Dark Universe - January 17, 2020 **Category: **Physics **Source Type: **research

**Simulation of primordial black hole formation using pseudo-spectral methods**

Publication date: Available online 14 January 2020Source: Physics of the Dark UniverseAuthor(s): Albert EscrivàAbstractIn this work we have used for the first time pseudo-spectral methods to perform numerical simulations of spherically symmetric black hole formations on a Friedman-Robertson-Walker universe. With these methods, the differential equations describing the gravitational collapse are partially solved algebraically. With our publicly available code we then independently check, and confirm, previous numerical estimations of the thresholds to form primordial black holes. By using an excision technique and an...

**Source: **Physics of the Dark Universe - January 15, 2020 **Category: **Physics **Source Type: **research

**On the absence of a universal surface density, and a maximum Newtonian acceleration in dark matter haloes: Consequences for MOND**

Publication date: Available online 13 January 2020Source: Physics of the Dark UniverseAuthor(s): Yong Zhou, A. Del Popolo, Zhe ChangAbstractWe study the dark matter (DM) surface density using the SPARC sample and compare it to Donato et al. (2009) result. By means of MCMC method, we infer the best-fitting parameters for each galaxy. We reobtain the scaling relation between the surface density and luminosity, and several other scaling laws relating the dark matter halo properties to that of the galactic disc properties. We conclude, in contrast with Donato et al. (2009), that the dark matter surface density is not...

**Source: **Physics of the Dark Universe - January 14, 2020 **Category: **Physics **Source Type: **research

**Searching for axino-like particle at fixed target experiments**

Publication date: Available online 10 January 2020Source: Physics of the Dark UniverseAuthor(s): Ki-Young Choi, Takeo Inami, Kenji Kadota, Inwoo Park, Osamu SetoAbstractWe investigate the detectability of axino-like particle, which is defined as a supersymmetric partner of axion-like particle and can be a good candidate for dark matter in our Universe. Especially, we consider the fixed target experiments to search for the light axino-like particle with a neutralino as the next-to-lightest supersymmetric particle. We calculate the production and decay rate of neutralinos and the consequent number of events (such as photons ...

**Source: **Physics of the Dark Universe - January 11, 2020 **Category: **Physics **Source Type: **research

**Traversable wormhole solutions in Rastall teleparallel gravity**

Publication date: Available online 10 January 2020Source: Physics of the Dark UniverseAuthor(s): Kh. Saaidi, N. NazavariAbstractIn this manuscript we consider the traversable wormhole solutions in teleparallel gravity formalism with and without Rastall constraint on perfect fluid stress–energy tensor. We have studied the isotropic and non-isotropic form of stress–energy tensor of ideal fluid which the equation of state (EoS) between density and the radial components of pressure is used. This work is done for a diagonal tetrad and we have found some geometries which could describe a traversable wormhole, but the...

**Source: **Physics of the Dark Universe - January 11, 2020 **Category: **Physics **Source Type: **research

**A coupled generalized three-form dark energy model**

Publication date: Available online 10 January 2020Source: Physics of the Dark UniverseAuthor(s): Yan-Hong Yao, Xin-He MengAbstractA coupled dark energy model is considered, in which dark energy is represented by a generalized three-form field and dark matter by dust. By assuming the functions N and I in the model’s Lagrangian as two power-law functions of the three-form field, we obtain two fixed points of the autonomous system of evolution equations, consisting of a attractor and a tracking saddle point which can be used to alleviate the coincidence problem. After marginalizing the present three-form field κX0...

**Source: **Physics of the Dark Universe - January 11, 2020 **Category: **Physics **Source Type: **research

**Beautiful form of Geff in EiBI gravity via the Ward–Kodama entropy-area law**

Publication date: January 2020Source: Physics of the Dark Universe, Volume 27Author(s): Narakorn KaewkhaoAbstractAn elegant form of the effective gravitational constant, Geff=2GNU2+V2, has been evaluated under the scope of EiBI Universe via the Wald-Kodama entropy-area law. ĠeffGeff together with the modified FLRW metric are used to conduct the evolutionary phases of the Universe. EiBI parameter was limited in the range 8.60×1047m2≲b≲4.31×1049m2 with the Lunar Laser Ranging (LLB) constraint. The multiplication of EiBI parameter and the cosmological constant are significantly confined in the range 1.12&tim...

**Source: **Physics of the Dark Universe - January 10, 2020 **Category: **Physics **Source Type: **research

**Beautiful form of Geff in EiBI gravity via the Ward-Kodama entropy-area law**

Publication date: Available online 7 January 2020Source: Physics of the Dark UniverseAuthor(s): Narakorn KaewkhaoAbstractAn elegant form of the effective gravitational constant, Geff=2GNU2+V2, has been evaluated under the scope of EiBI Universe via the Wald-Kodama entropy-area law. ĠeffGeff together with the modified FLRW metric are used to conduct the evolutionary phases of the Universe. EiBI parameter was limited in the range 8.60×1047m2≲b≲4.31×1049m2 with the Lunar Laser Ranging (LLB) constraint. The multiplication of EiBI parameter and the cosmological constant are significantly confined in the range ...

**Source: **Physics of the Dark Universe - January 8, 2020 **Category: **Physics **Source Type: **research

**Discrimination of anisotropy in dark matter velocity distribution with directional detectors**

In this study, the possibility of discriminating between isotropic and anisotropic distributions is investigated through numerical simulations with a directional detector. The numerical simulation is performed for two cases. These cases are classified according to detectors as follows: one corresponds to an angular histogram distribution of the signals whereas the other corresponds to an energy-angular distribution of the signals. In order to discriminate the energy-angular distributions, a chi-squared test between ideal data set and experimental data and likelihood estimation are proposed. The anisotropy of the velocity d...

**Source: **Physics of the Dark Universe - January 5, 2020 **Category: **Physics **Source Type: **research

**Late time cosmic acceleration in modified Sáez–Ballester theory**

Publication date: January 2020Source: Physics of the Dark Universe, Volume 27Author(s): S.M.M. Rasouli, R. Pacheco, M. Sakellariadou, P.V. MonizAbstractWe establish an extended version of the modified Sáez–Ballester (SB) scalar–tensor theory in arbitrary dimensions whose energy momentum tensor as well as potential are pure geometrical quantities. This scenario emerges by means of two scalar fields (one is present in the SB theory and the other is associated with the extra dimension) which widens the scope of the induced-matter theory. Moreover, it bears a close resemblance to the standard Sáez&nda...

**Source: **Physics of the Dark Universe - January 4, 2020 **Category: **Physics **Source Type: **research

**SKA-Phase 1 sensitivity to synchrotron radio emission from multi-TeV Dark Matter candidates**

Publication date: Available online 30 December 2019Source: Physics of the Dark UniverseAuthor(s): Jose A.R. Cembranos, Álvaro de la Cruz-Dombriz, Viviana Gammaldi, Miguel Méndez-IslaAbstractIn the era of radio astronomy, the high sensitivity of the Square Kilometre Array (SKA) could play a decisive role in the detection of new radio sources. In this work, we study the SKA sensitivity to the synchrotron radio emission expected by the annihilation of TeV DM candidate in the Draco dwarf spheroidal galaxy. On the one hand, we consider model-independent DM candidates: we find out that with 1000 h of data-taki...

**Source: **Physics of the Dark Universe - January 1, 2020 **Category: **Physics **Source Type: **research

**Observational constraints on DBI constant-roll inflation**

Publication date: Available online 30 December 2019Source: Physics of the Dark UniverseAuthor(s): Tayeb Golanbari, Abolhassan Mohammadi, Khaled SaaidiAbstractUsing the constant-roll approach, DBI inflationary scenario will be studied and it is sought to compare the result with observational data. By considering the cosmological perturbations of the model, it is realized that some extra terms appear in the amplitude of scalar perturbations which indicates that there should be a modified version of the scalar spectral index and tensor-to-scalar ratio. To compare the model with observational data, some specific functions of t...

**Source: **Physics of the Dark Universe - January 1, 2020 **Category: **Physics **Source Type: **research

**Late time cosmic acceleration in modified Sáez-Ballester theory**

Publication date: Available online 28 December 2019Source: Physics of the Dark UniverseAuthor(s): S.M.M. Rasouli, R. Pacheco, M. Sakellariadou, P.V. MonizAbstractWe establish an extended version of the modified Sáez-Ballester (SB) scalar-tensor theory in arbitrary dimensions whose energy momentum tensor as well as potential are pure geometrical quantities. This scenario emerges by means of two scalar fields (one is present in the SB theory and the other is associated with the extra dimension) which widens the scope of the induced-matter theory. Moreover, it bears a close resemblance to the standard Sáez-Balle...

**Source: **Physics of the Dark Universe - December 29, 2019 **Category: **Physics **Source Type: **research

**Lorentz violation with an invariant minimum speed as foundation of the Gravitational Bose Einstein Condensate of a Dark Energy Star**

Publication date: Available online 27 December 2019Source: Physics of the Dark UniverseAuthor(s): Cláudio Nassif Cruz, Rodrigo Francisco dos Santos, A.C. Amaro de FariaAbstractWe aim to search for the connection between the spacetime with an invariant minimum speed so-called Symmetrical Special Relativity (SSR) with Lorentz violation and the Gravitational Bose Einstein Condensate (GBEC) as the central core of a star of gravitational vacuum (gravastar), where one normally introduces a cosmological constant for representing an anti-gravity. This usual model of gravastar with an equation of state (EOS) for vacuum energ...

**Source: **Physics of the Dark Universe - December 29, 2019 **Category: **Physics **Source Type: **research

**Black hole remnant in massive gravity**

Publication date: Available online 24 December 2019Source: Physics of the Dark UniverseAuthor(s): B. Eslam Panah, S.H. Hendi, Y.C. OngAbstractThe possibility of a nonzero graviton mass has been widely pursued in the literature. In this work we investigate a black hole solution in massive gravity with a degenerate fiducial metric often used in the literature. We find that the end state of Hawking evaporation leads to black hole remnant, which could help to ameliorate the information paradox. We prove that these remnants only exist in anti-de Sitter spacetime. Nevertheless, we speculate on their possible relevance to our Uni...

**Source: **Physics of the Dark Universe - December 25, 2019 **Category: **Physics **Source Type: **research

**What is the amplitude of the gravitational waves background expected in the Starobinski model?**

Publication date: Available online 24 December 2019Source: Physics of the Dark UniverseAuthor(s): Fabrizio Renzi, Mehdi Shokri, Alessandro MelchiorriAbstractThe inflationary model proposed by Starobinski in 1979 predicts an amplitude of the spectrum of primordial gravitational waves, parametrized by the tensor to scalar ratio, of r=0.0037 in case of a scalar spectral index of nS=0.965. This amplitude is currently used as a target value in the design of future CMB experiments with the ultimate goal of measuring it at more than five standard deviations. Here we evaluate how stable are the predictions of the Starobinski model...

**Source: **Physics of the Dark Universe - December 25, 2019 **Category: **Physics **Source Type: **research

**Charged anisotropic compact star in f(R,T) gravity: A minimal geometric deformation gravitational decoupling approach**

This article is devoted to the study of high dense charged anisotropic compact structures in the framework of f(R,T) gravity theory. The principal aims of this investigation, regard the extension of the isotropic Durgapal-Fuloria model within the context of charged isotropic f(R,T) solutions. The second main goal of this work is to apply the gravitational decoupling via a minimal geometric deformation (MGD) scheme in f(R,T) gravity. Finally, the third one is to derive an anisotropic version of the charged isotropic model previously obtained by applying gravitational decoupling technology. This MGD approach splits the syste...

**Source: **Physics of the Dark Universe - December 20, 2019 **Category: **Physics **Source Type: **research

**Noether symmetries in interacting quintessence cosmology**

Publication date: Available online 19 December 2019Source: Physics of the Dark UniverseAuthor(s): Ester Piedipalumbo, Mariafelicia De Laurentis, Salvatore CapozzielloAbstractThe Noether Symmetry Approach is applied to interacting quintessence cosmology with the aim to search for exact solutions and select scalar-field self-interaction potentials. It turns out that the solutions found are compatible with the accelerated expansion of the Universe and with observational dataset, as the SNeIa Pantheon data. (Source: Physics of the Dark Universe)

**Source: **Physics of the Dark Universe - December 19, 2019 **Category: **Physics **Source Type: **research

**Sublunar-mass primordial black holes from closed axion domain walls**

Publication date: Available online 17 December 2019Source: Physics of the Dark UniverseAuthor(s): Shuailiang GeAbstractWe study the formation of primordial black holes (PBHs) from the collapse of closed domain walls (DWs) which naturally arise in QCD axion models near the QCD scale together with the main string-wall network. The size distribution of the closed DWs is determined by percolation theory, from which we further obtain PBH mass distribution and abundance. Various observational constraints on PBH abundance in turn also constrain QCD axion parameter space. Our model prefers axion mass at the meV scale (fa∼109 G...

**Source: **Physics of the Dark Universe - December 19, 2019 **Category: **Physics **Source Type: **research

**Greybody factor for quintessential Kerr–Newman black hole**

Publication date: Available online 14 December 2019Source: Physics of the Dark UniverseAuthor(s): M. Sharif, Qanitah Ama-Tul-MughaniAbstractIn this paper, we formulate an analytic expression of the greybody factor for the Kerr–Newman black hole in the presence of the quintessential field. Primarily, we analyze the profile of effective potential by transforming the radial equation of motion into standard Schrödinger form through tortoise coordinate. The two asymptotic solutions, in the form of hypergeometric functions, are computed at distinct radial regions such as a black hole and cosmological horizons determin...

**Source: **Physics of the Dark Universe - December 16, 2019 **Category: **Physics **Source Type: **research

**Suppression of the long-wavelength CMB spectrum from the Hartle–Hawking wave function in the Starobinsky-type inflation model**

Publication date: January 2020Source: Physics of the Dark Universe, Volume 27Author(s): Pisin Chen, Hsiao-Heng Yeh, Dong-Han YeomAbstractThe lack of correlations on the large scale cosmic microwave background (CMB) anisotropy provides a potential window to probe beyond the standard inflationary scenario. In this paper, we investigate the primordial power spectrum based on the Hartle–Hawking (HH) no-boundary proposal for a homogeneous, isotropic, and spatially-closed universe that leads to Starobinsky-type inflation after the classicalization. While we found that there is no suppression at large scales in the standard...

**Source: **Physics of the Dark Universe - December 16, 2019 **Category: **Physics **Source Type: **research

**Buchdahl model in f(R,T) gravity: A comparative study with standard Einstein’s gravity**

Publication date: Available online 12 December 2019Source: Physics of the Dark UniverseAuthor(s): S.K. Maurya, Ayan Banerjee, Francisco Tello-OrtizAbstractThis 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 Ri...

**Source: **Physics of the Dark Universe - December 13, 2019 **Category: **Physics **Source Type: **research

**Distance, de Sitter and trans-Planckian censorship conjectures: The status quo of Warm inflation**

Publication date: Available online 12 December 2019Source: Physics of the Dark UniverseAuthor(s): Suratna DasAbstractIn this short note, we pointed out that Warm inflationary scenario remains to be favoured over its cold counterpart by the recently proposed conjectures, which aim to overrule de Sitter like constructions in String Landscapes. On the other hand, the canonical cold (single-field slow-roll) inflationary models, which were in tension with the previously proposed de Sitter conjecture, have now become even more unlikely to realise in String Landscapes as these scenarios fail to cope up with both the conjectures, ...

**Source: **Physics of the Dark Universe - December 13, 2019 **Category: **Physics **Source Type: **research

**Connecting particle physics and cosmology: measuring the dark matter relic density in compressed supersymmetry models at the LHC**

Publication date: Available online 12 December 2019Source: Physics of the Dark UniverseAuthor(s): Carlos Avila, Andrés Flórez, Alfredo Gurrola, Dale Julson, Savanna StarkoAbstractThe identity of Dark Matter (DM) is one of the relevant topics in particle physics today. The R-parity conserving Minimal Supersymmetric Standard Model (MSSM), which naturally provides a DM candidate in the form of the lightest neutralino (χ̃10), is used as a benchmark scenario to show that a measurement of the DM relic density, Ωχ̃10h2, can be achieved from measurements at the CERN Large Hadron Collider. Focus is pla...

**Source: **Physics of the Dark Universe - December 13, 2019 **Category: **Physics **Source Type: **research

**Suppression of the long-wavelength CMB spectrum from the Hartle-Hawking wave function in the Starobinsky-type inflation model**

Publication date: Available online 12 December 2019Source: Physics of the Dark UniverseAuthor(s): Pisin Chen, Hsiao-Heng Yeh, Dong-Han YeomAbstractThe lack of correlations on the large scale cosmic microwave background (CMB) anisotropy provides a potential window to probe beyond the standard inflationary scenario. In this paper, we investigate the primordial power spectrum based on the Hartle-Hawking (HH) no-boundary proposal for a homogeneous, isotropic, and spatially-closed universe that leads to Starobinsky-type inflation after the classicalization. While we found that there is no suppression at large scales in the stan...

**Source: **Physics of the Dark Universe - December 13, 2019 **Category: **Physics **Source Type: **research

**No chiral light bending by clumps of axion-like particles**

Publication date: January 2020Source: Physics of the Dark Universe, Volume 27Author(s): Diego Blas, Andrea Caputo, Mikhail M. Ivanov, Laura SbernaAbstractWe study the propagation of light in the presence of a parity-violating coupling between photons and axion-like particles (ALPs). Naively, this interaction could lead to a split of light rays into two separate beams of different polarization chirality and with different refraction angles. However, by using the eikonal method we explicitly show that this is not the case and that ALP clumps do not produce any spatial birefringence. This happens due to non-trivial variations...

**Source: **Physics of the Dark Universe - December 13, 2019 **Category: **Physics **Source Type: **research

**Waves of space–time from a collapsing compact object**

Publication date: Available online 10 December 2019Source: Physics of the Dark UniverseAuthor(s): Jaime Mendoza Hernández, Juan Ignacio Musmarra, Mauricio BelliniAbstractWe study the partial time dependent collapse of a spherically symmetric compact object with initial mass M1+M2 and final mass M2 and the waves of space–time emitted during the collapse via back-reaction effects. We obtain exact analytical solutions for the waves of space–time in an example in which M1=M2=(M1+M2)∕2. The wavelengths of the space–time emitted waves during the collapse have the cut (we use natural units c=ħ=1): λ

**Source: **Physics of the Dark Universe - December 11, 2019 **Category: **Physics **Source Type: **research

**Redshifted 21-cm emission signal from the halos in Dark Ages**

Publication date: Available online 23 November 2019Source: Physics of the Dark UniverseAuthor(s): Bohdan Novosyadlyj, Valerii Shulga, Yurii Kulinich, Han WeiAbstractThe emission in the hyperfine structure 21 cm line of atomic hydrogen arising in the halos with masses ∼106−1010 M⊙ from the Dark Ages in the models with Warm Dark Matter (WDM) is analysed. The halos are assumed to be formed from Gaussian density peaks of cosmological density perturbations at 10≲z≲50. Semi-analytical modelling of the formation of individual spherical halos in multi-component models shows that gas in them has the kinetic tem...

**Source: **Physics of the Dark Universe - November 24, 2019 **Category: **Physics **Source Type: **research

**Effects of neutron stars magnetic dipole on the generation of gravitational waves**

Publication date: Available online 21 November 2019Source: Physics of the Dark UniverseAuthor(s): Mattia VillaniAbstractIn this paper we shall consider the potential effect of the magnetic dipole moment of a neutron star (NS) in a binary NS-NS system.We shall derive the Lagrangian of the binary system and show how to find a Multipolar Post Minkowskian (MPM) solution to the linearized Einstein-Maxwell system and the energy flux of the electromagnetic waves; we shall calculate at the higher order the equations of motion and precession. At the end, we will provide calculations proving that the effect of the magnetic moment on...

**Source: **Physics of the Dark Universe - November 22, 2019 **Category: **Physics **Source Type: **research

**Quantization of the nonstandard propagating gravitational waves in the cosmological background**

Publication date: Available online 20 November 2019Source: Physics of the Dark UniverseAuthor(s): S.X. Tian, Zong-Hong ZhuAbstractDetections of gravitational wave (GW) stimulate the discussion of how GWs propagate in the expanding Universe. General relativity predicts that GWs are massless and propagate at the speed of light with no extra friction term, which relates to the attenuation of GWs, while some modified gravities may predict a different behavior. The mass and speed terms can be tightly constrained by the GW150914-like and GW170817/GRB 170817A events, respectively. However, the friction term remaining unconstraine...

**Source: **Physics of the Dark Universe - November 21, 2019 **Category: **Physics **Source Type: **research

**Low-redshift constraints on homogeneous and isotropic universes with torsion**

Publication date: Available online 19 November 2019Source: Physics of the Dark UniverseAuthor(s): C.M.J. Marques, C.J.A.P. MartinsAbstractOne of the possible extensions of Einstein’s General Theory of Relativity consists in allowing for the presence of spacetime torsion. The form of the underlying torsion tensor can be chosen such that the homogeneity and isotropy of Friedmann–Lemaitre–Robertson–Walker universes is preserved, and it has been recently suggested that such universes may undergo accelerating phases. We use recent low-redshift data, coming from Type Ia Supernova and Hubble parameter meas...

**Source: **Physics of the Dark Universe - November 19, 2019 **Category: **Physics **Source Type: **research