1,721,195 research outputs found
Born–Infeld condensate as a possible origin of neutrino masses and dark energy
No full textAbstractWe discuss the possibility that a Born–Infeld condensate coupled to neutrinos can generate both neutrino masses and an effective cosmological constant. In particular, an effective field theory is provided capable of dynamically realizing the neutrino superfluid phase firstly suggested by Ginzburg and Zharkov. In such a case, neutrinos acquire a mass gap inside the Born–Infeld ether forming a long-range Cooper pair. Phenomenological implications of the approach are also discussed
Modified gravity: the game of theories?
No full textThis mini-review is devoted to the memory of Professor Vladislav Gavrilovich Bagrov, the outstanding Russian physicist, who was especially dedicated to mathematical physics. Amazingly, he heard the music of differential equations obtained from field equations. I belong to the school of theoretical physics created by Prof. Bagrov in Tomsk, where he was my first teacher in mathematical physics and PhD thesis director. In this review, I briefly discuss several popular models of modified gravity in relation with observational data. Note that reasonable modified gravities lead to extremely complicated field equations, which solution can be a real challenge for Prof. Bagrov and his pupils. This is an attempt to look over the horizon in order to understand which final theory may better describe the universe evolution history so that to be the best candidate for understanding gravitational physics and the universe history.This work was financially supported by the Program Unidad de Excelencia Maria de Maeztu CEX2020-001058-M.With funding from the Spanish government through the "María de Maeztu Unit of Excellence" accreditation (CEX2020-001058-M).Peer reviewe
ACT inflation and its influence on reheating era in Einstein-Gauss-Bonnet gravity
No full textWe investigate the observational viability of non-minimally coupled scalar-Einstein-Gauss-Bonnet (GB) gravity, during inflation and post-inflationary reheating dynamics, from the perspective of the latest ACT-DR6 combined with the Planck 2018 and BAO data. It turns out that the ACT result considerably affects the inflationary e-fold number compared to the case where only Planck 2018 data is taken into account. The viable parameter spaces corresponding to the inflationary ACT-DR6+Planck18+BAO substantially influence the reheating phenomenology via the reheating equation of state ( w eff ) and the reheating temperature. In particular, the ACT-DR6+Planck18+BAO data seems to disfavor w eff < 1 / 3 during the reheating stage, which is unlike to that of only Planck 2018 case. These reveal how the ACT-DR6 data hits the early universe phenomenology from inflation to reheating in the context of higher curvature like scalar-Einstein-GB theory of gravity.No fundingPeer reviewe
Mass-radius relation for neutron stars inf(R)gravity
Get PDFWe discuss the mass-radius diagram for static neutron star models obtained by the numerical solution of modified Tolman-Oppenheimer-Volkoff equations in f (R ) gravity where the Lagrangians f (R )=R +α R2(1 +γ R ) and f (R )=R1 +∊ are adopted. Unlike the case of the perturbative approach previously reported, the solutions are constrained by the presence of an extra degree of freedom, coming from the trace of the field equations. In particular, the stiffness of the equation of state determines an upper limit on the central density ρc above which the positivity condition of energy-matter tensor trace Tm=ρ -3 p holds. In the case of quadratic f (R ) gravity, we find higher masses and radii at lower central densities with an inversion of the behavior around a pivoting ρc which depends on the choice of the equation of state. When considering the cubic corrections, we find solutions converging to the required asymptotic behavior of the flat metric only for γ 1 +∊ considering ∊ as the leading parameter. We work strictly in the Jordan frame in order to consider matter minimally coupled with respect to geometry. This fact allows us to avoid ambiguities that could emerge in adopting the Einstein frame. <P /
Nonperturbative models of quark stars in f(R) gravity
No full textAbstractQuark star models with realistic equation of state in nonperturbative f(R) gravity are considered. The mass-radius relation for f(R)=R+αR2 model is obtained. Considering scalar curvature R as an independent function, one can find out, for each value of central density, the unique value of central curvature for which one has solutions with the required asymptotic R→0 for r→∞. In other words, one needs a fine-tuning for R to achieve quark stars in f(R) gravity. We consider also the analogue description in corresponding scalar-tensor gravity. The fine-tuning on R is equivalent to the fine-tuning on the scalar field ϕ in this description. For distant observers, the gravitational mass of the star increases with increasing α (α>0) but the interpretation of this fact depends on frame where we work. Considering directly f(R) gravity, one can say that increasing of mass occurs by the “gravitational sphere” outside the star with some “effective mass”. On the other hand, in conformal scalar-tensor theory, we also have a dilaton sphere (or “disphere”) outside the star but its contribution to gravitational mass for distant observer is negligible. We show that it is possible to discriminate modified theories of gravity from General Relativity due to the gravitational redshift of the thermal spectrum emerging from the surface of the star
Structural features of low-stable phase states of aqueous solutions at ultrahigh dilution
No full textA physical concept of thermodynamic structural-phase states of a physical system is proposed in application to ultrahigh diluted aqueous solutions low-stable to external impacts. The physical analogy between the states of these solutions and the condensed physical systems helps to understand physics of various effects observed in ultrahigh diluted aqueous solutions. In particular, this approach allows the role of shaking of the chemical solutions in the Epstein effect to be evaluated by mechanochemical methods. An analysis of the thermodynamic and structural-phase low-stable states of the physical system makes it possible to propose a possible mechanism for the system transition to a new phase state under a low-stable external impact on the example of an ordering alloy system. In this case, the small external impact (for example, shaking) can lead to significant phase changes of the system state in which the structural units are close thermodynamically, but can differ significantly in symmetry. It is discussed how the effect of the state of the suitable symmetric liquid solution of a substance under a small external impact (for example, in the form of shaking) can be experimentally realized.The authors did not receive support from any organization for the submitted work.Peer reviewe
Chaotic solutions and black hole shadow in f(R) gravity
No full textWe discuss the emergence of black hole shadow and photon-sphere in the context of f(R) gravity. It is shown that the shadow is exponentially sensitive to linear instabilities of metric coming from some f(R) solutions. Thus, the instabilities of photon circular trajectories, delimiting the black hole photon-sphere, are double exponentialized. Specifically we individuate two Lyapunov exponents, rather than only one, related to two different sources of chaos in geodesic orbits as a sort of butterfly effect. Such a result violates the black hole chaos bound proposed by Maldacena, Shenker and Stanford for General Relativity. We also explore the impact of the black hole metric instabilities in f(R) gravity on the quasi-normal modes. In the framework of Extended Theories of Gravity, our analysis suggests a new paradigm to deal with black hole shadow and gravitational waves observations coming from black hole merging in the ringdown phase.The work of A.A. is supported by the Talent Scientific Research Program of College of Physics, Sichuan University, Grant No. 1082204112427. S.C. acknowledge the support of Istituto Nazionale di Fisica Nucleare (INFN) (iniziative specifiche MOONLIGHT2 and QGSKY)
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