Cosmological Constant Research Papers - Academia.edu (original) (raw)

It is extraordinary that a number of observations indicate that we live in a spatially flat, low matter density Universe, which is currently undergoing a period of accelerating expansion. The effort to explain this current state has focused attention on cosmological models in which the dominant component of the cosmic energy density has negative pressure, with an equation of state w ≥ −1. Remarking that most observations are consistent with models right up to the w = −1 or cosmological constant (Λ) limit, it is natural to ask what lies on the other side, at w < −1. In this regard, we construct a toy model of a "phantom" energy component which possesses an equation of state w < −1. Such a component is found to be compatible with most classical tests of cosmology based on current data, including the recent type 1a SNe data as well as the cosmic microwave background anisotropy and mass power spectrum. If the future observations continue to allow w < −1, then barring unanticipated systematic effects, the dominant component of the cosmic energy density may be stranger than anything expected.

- by V. Pleitez
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- Quantum Gravity, Cosmological Constant, Spontaneous symmetry breaking

It is likely that the holographic principle will be a consequence of the would be theory of quantum gravity. Thus, it is interesting to try to go in the opposite direction: can the holographic principle fix the gravitational interaction? It is shown that the classical gravitational interaction is well inside the set of potentials allowed by the holographic principle. Computations clarify which role such a principle could have in lowering the value of the cosmological constant computed in QFT to the observed one.

- by G. Vilasi
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- Physics, Quantum Gravity, Gravity, Key words

We consider an 8-dimensional gravitational theory, which possesses a principle fiber bundle structure, with Lorentz-scalar fields coupled to the metric. One of them plays the role of a Higgs field and the other one that of a dilaton field. The effective cosmological constant is interpreted as a Higgs potential. The Yukawa couplings are introduce by hand. The extra dimensions constitute a SU (2) L × U (1) Y × SU (2) R group manifold. Dirac fields are coupled to the potentials derived from the metric. As result, we obtain an effective four-dimensional theory which contains all couplings of a Weinberg-Salam-Glashow theory in a curved space-time. The masses of the gauge bosons and of the first two fermion families are given by the theory.

- by Alfredo Macias
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- Physics, Space Time, Cosmological Constant

We discuss how to extract information about the cosmological constant from the Wheeler-DeWitt equation, considered as an eigenvalue of a Sturm-Liouville problem. The equation is approximated to one loop with the help of a variational approach with Gaussian trial wave functionals. A canonical decomposition of modes is used to separate transverse-traceless tensors (graviton) from ghosts and scalar. We show that no ghosts appear in the final evaluation of the cosmological constant. A zeta function regularization is used to handle with divergences. A renormalization procedure is introduced to remove the infinities together with a renormalization group equation. A brief discussion on the extension to a f(R) theory is considered.

In this work we study a Newtonian cosmological model in the context of a Noncommutative space. We show that the trajectories of test particles undergo modifications by considering a simplectic structure with a noncommutative parameter, \Theta, in the coordinates. In the case of a positive cosmological constant, we obtain trajectories which develop spirals and we also find a correction to the Hubble constant. We finally show that in the strong \Theta limit, there is a relation with a Godel-type metric.

We present an exact solution of Einstein's field equations in toroidal coordinates. The solution has three regions: an interior with a string equation of state; an Israel boundary layer; and an exterior with constant isotropic pressure and constant density, locally isometric to anti-de Sitter space-time. The exterior can be a cosmological vacuum with negative cosmological constant. The size and mass of the toroidal loop depend on the size of Lambda.

- by Jean Krisch
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- Mathematical Physics, Field Theory, Quantum Field Theory, Mathematical Sciences

I proposed a new expansion force to explain the flat rotation curves of plane galaxies, in a Newtonian approach in 2016. This force is validated here in General Relativity for an inhomogeneous radially symmetrical universe. It can be deduced from the solution of Einstein's equation with a cosmological constant. A pseudo-Schwarzschild "twin-potential" metric is considered, with two different potentials for the space and time dimensions. The expansion force results as a repulsive dual gravity. Negative masses are needed. The necessary mass repartitions are computed, in connection with the radial dynamics and the expansion rate's evolution. A linear model and a quadratic model are studied, connected with the observation representations of a universe in accelerated expansion. It is a first step towards a better representation of an inhomogeneous universe. The framework can be applied to deduce the universe mass repartition form the measured values of the expansion rate variation. Résumé J'ai proposé en 2016 une nouvelle force d'expansion pour expliquer les courbes de rotation plates des galaxies spirales dans une approche Newtonienne. Cette force est validée ici dans le cadre de la Relativité Générale pour un univers inhomogène à symétrie radiale. On peut la déduire comme solution de l'équation d'Einstein avec Constante Cosmologique. On considère une métrique à « potentiels jumelés », avec deux potentiels différents pour les dimensions spatiales et temporelles. Il en résulte une force d'expansion agissant comme une gravité duale répulsive. Il faut des masses négatives. On calcule les répartitions de masses nécessaires, en liaison avec la dynamique radiale et l'évolution du taux d'expansion. On étudie un modèle linéaire et un modèle quadratique, en lien avec les représentations d'un univers observé en expansion accélérée. Il s'agit là d'une première étape vers une meilleure représentation d'un univers inhomogène. Ce cadre peut être appliqué pour déduire la répartition de masses de l'univers à partir des valeurs mesurées du taux d'expansion.

- by Jacques Fleuret
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- Universe expansion, Gravity, Gravity Model, Solutions of Einstein Field Equations

We discuss the influence of the cosmological constant on the gravitomagnetic clock effect and the gravitational time delay of electromagnetic rays. Moreover, we consider the relative motion of a binary system to linear order in the cosmological constant Λ. The general expression for the effect of Λ on pericenter precession is given for arbitrary orbital eccentricity.

- by Bahram Mashhoon
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- Mathematical Sciences, Physical sciences, Linear Order, Cosmological Constant

It will be argued here that the cosmological constant problem exists because of the way the vacuum is defined in quantum field theory. It has been known for some time that for QFT to be gauge invariant certain terms--such as part of the vacuum polarization tensor--must be eliminated either explicitly or by some form of regularization followed by renormalization. It has recently been shown that lack of gauge invariance is a result of the way the vacuum is defined, and redefining the vacuum so that the theory is gauge invariant may also offer a solution to the cosmological constant problem.

- by Gerald Marsh
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- Physics, Quantum Cosmology, Quantum Field Theory, Cosmological Constant

We derive quantization relations in the case when torsion effects are added in a De Sitter spacetime metric with or without a black hole at the Planck mass and Planck length limit. To this end we use Zeldovich's definition of the... more

- by Dr. Ioannis Haranas
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- Black Hole, Cosmological Constant, De Sitter

In this paper (part II), we analyze some Measure Theory equations and Ramanujan formulas with the developments of the MRB Constant. We obtain new possible mathematical connections with some Cosmological parameters and sectors of String... more

- by Michele Nardelli
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- Number Theory, Measure Theory, String Theory, Supersymmetry breaking

In this paper we consider the implications of a cosmological constant for the evolution of the universe, under a set of assumptions motivated by the holographic and horizon complementarity principles. We discuss the "causal patch" description of spacetime required by this framework, and present some simple examples of cosmologies described this way. We argue that these assumptions inevitably lead to very deep paradoxes, which seem to require major revisions of our usual assumptions.

- by Matthew Kleban
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- High Energy Physics, Cosmological Constant

We present a class of simple scalar-tensor models of gravity with one scalar field (dilaton Phi\PhiPhi) and only one unknown function (cosmological potential U(Phi)U(\Phi)U(Phi)). These models might be considered as a stringy inspired ones with broken SUSY. They have the following basic properties: 1) Positive dilaton mass, mPhim_\PhimPhi, and positive cosmological constant Lambda\LambdaLambda, define two extremely different scales. The models under consideration are consistent with the known experimental facts if mPhi>10−3eVm_\Phi > 10^{-3} eVmPhi>10−3eV and Lambda=Lambdaobssim10−56cm−2\Lambda=\Lambda^{obs}\sim 10^{-56} cm^{-2}Lambda=Lambdaobssim10−56cm−2. 2) Einstein week equivalence principle is strictly satisfied and extended to scalar-tensor theories of gravity using a novel form of principle of "constancy of fundamental constants". 3) The dilaton plays simultaneously role of inflation field and quintessence field and yields a sequential hyper-inflation with graceful exit to asymptotic de Sitter space-time which is an attractor, and is approached as exp(−sqrt3Lambdaobsct/2)\exp(-\sqrt{3\Lambda^{obs}} ct/2)exp(−sqrt3Lambdaobsct/2). The time duration of inflation is DeltatinflsimmPhi−1\Delta t_{infl} \sim m_\Phi^{-1}DeltatinflsimmPhi−1. 4) Ultra-high frequency ($\omega_\Phi \sim m_\Phi$) dilatonic oscillations take place in asymptotic regime. 5) No fine tuning. (The Robertson-Walker solutions of general type have the above properties.) 6) A novel adjustment mechanism for cosmological constant problem seems to be possible: the huge value of cosmological constant in the stringy frame is re-scaled to its observed value by dilaton after transition to phenomenological frame.

- by Plamen Fiziev
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- Quantum Cosmology, High Energy Physics, Astrophysics, Oscillations

We study candidate vacuum configurations in ten-dimensional 0(32) and E 8 X E 8 supergravity and superstring theory that have unbroken N = 1 supersymmetry in four dimensions. This condition permits only a few possibilities, all of which have vanishing cosmological constant. In the E 8 × E 8 case, one of these possibilities leads to a model that in four dimensions has an E 6 gauge group with four standard generations of fermions.

- by Gary Horowitz and +1
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- Mathematical Physics, Quantum Physics, Bibliography, Supersymmetry

Over the last decade, there has been a respectable level of scientific interest regarding the concept of a ‘warp drive’. This is a hypothetical propulsion device that could theoretically circumvent the traditional limitations of special relativity which restricts spacecraft to sub-light velocities. Any breakthrough in this field would revolutionize space exploration and open the doorway to interstellar travel. This article discusses a novel approach to generating the ‘warp bubble’ necessary for such propulsion; the mathematical details of this theory are discussed in an article published in the Journal of the British Interpanetary Society [1]. The theory is based on some of the exciting predictions coming out of string theory and it is the aim of this article to introduce the warp drive idea from a non-mathematical perspective that should be accessible to a wide range of readers.

- by Gerald B Cleaver
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- String Theory, Warp Drive, Space Travel, Cosmological Constant

Rising to Mach, the problem of establishing the unity of the physical essence of the Universe on all space-time scales of its evolution is, apparently, one of the main problems in contemporary epistemology. The issues are primarily related to the problems of the dynamics of the Universe, namely, the need to postulate hypothetical entities - dark energy and dark matter, whose nature is unknown, but whose contribution to the energy content of the Universe is about 95%. A "severe trial for the entire fundamental theory" turned out to be a discrepancy of 120 orders of magnitude between the experimentally established value of the cosmological constant and the calculated value of the energy density of the physical vacuum. Sharp questions arise also regarding the physical essence of gravitation and the nature of its unique smallness as compared with other interactions - nuclear ones, strong and weak, as well as electromagnetic ones. Sufficiently acute problems in the perception of the Universe as a single holistic system arise also at the level of microscales. First of all, we mean here the so called low-energy nuclear reactions, which are realized in the conditions of nonequilibrium low temperature plasma. The fundamental problems of such processes are usually not widely discussed, and many physicists are very critical of the very possibility of implementing such processes. Our main hypothesis for understanding the key problems of contemporary fundamental physics, including the indicated cosmological problems as well as a new class of electron-initiated nuclear chemical processes, is to introduce the basic reference system associated with the electromagnetic component of physical vacuum - EM vacuum of the expanding Universe, with a selection of global time t, being common for all points of the expanding Universe and measured starting from the time of t = 0, which corresponds to the Big Bang.

- by Serge Timashev
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- Quantum Electrodynamics, Dark Matter, Dark Energy, Big Bang

The discovery that the cosmic expansion is accelerating has been followed by an intense theoretical and experimental response in physics and astronomy. The discovery implies that our most basic notions about how gravity work are violated... more

- by Robert Caldwell
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- General Relativity, Dark Energy, Cosmology, Cosmological Constant
- by Blaise TCHAPNDA
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- Mathematics, Mathematical Physics, Physics, Quantum Physics

We dedicate this paper to Andrzej Kossakowski on the occasion of his 70 th birthday.

- by A. Kamenshchik
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- General Relativity, Special Relativity, Mathematical Sciences, Physical sciences

In this thesis, we explore three phenomenological alternatives to the current paradigm of the standard inflationary big bang scenario. The three alternative themes are spin torsion (or Einstein-Cartan-Kibble-Sciama) theories, extra dimensions (braneworld cosmology) and changing global symmetry. In the spin torsion theories, we found new cosmological solutions with a cosmological constant as alternative to the standard scalar field driven inflationary

- by Bernard Leong
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- Big Bang, Phase transition, Cosmological Constant, De Sitter

We construct the Extended Relativity Theory in Born-Clifford-Phase spaces with an upper R and lower length λ scales (infrared/ultraviolet cutoff ). The invariance symmetry leads naturally to the real Clifford algebra Cl(2, 6, R) and complexified Clifford Cl C (4) algebra related to Twistors. A unified theory of all Noncommutative branes in Clifford-spaces is developed based on the Moyal-Yang star product deformation quantization whose deformation parameter involves the lower/upper scale (hλ/R). Previous work led us to show from first principles why the observed value of the vacuum energy density (cosmological constant ) is given by a geometric mean relationship ρ ∼ L −2 P lanck R −2 = L −4 P (L P lanck /R) 2 ∼ 10 −122 M 4 P lanck , and can be obtained when the infrared scale R is set to be of the order of the present value of the Hubble radius. We proceed with an extensive review of Smith's 8D model based on the Clifford algebra Cl(1, 7) that reproduces at low energies the physics of the Standard Model and Gravity, including the derivation of all the coupling constants, particle masses, mixing angles, ....with high precision. Geometric actions are presented like the Clifford-Space extension of Maxwell's Electrodynamics, and Brandt's action related to the 8D spacetime tangentbundle involving coordinates and velocities ( Finsler geometries ). Finally we outline the reasons why a Clifford-Space Geometric Unification of all forces is a very reasonable avenue to consider and propose an Einstein-Hilbert type action in Clifford-Phase spaces (associated with the 8D Phase space) as a Unified Field theory action candidate that should reproduce the physics of the Standard Model plus Gravity in the low energy limit.

This is a review of the physics and cosmology of the cosmological constant. Focusing on recent developments, I present a pedagogical overview of cosmology in the presence of a cosmological constant, observational constraints on its... more

- by Sean Carroll
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- Science, Multidisciplinary, Cosmological Constant

In this paper we review in detail a number of approaches that have been adopted to try and explain the remarkable observation of our accelerating Universe. In particular we discuss the arguments for and recent progress made towards understanding the nature of dark energy. We review the observational evidence for the current accelerated expansion of the universe and present a number of dark energy models in addition to the conventional cosmological constant, paying particular attention to scalar field models such as quintessence, K-essence, tachyon, phantom and dilatonic models. The importance of cosmological scaling solutions is emphasized when studying the dynamical system of scalar fields including coupled dark energy. We study the evolution of cosmological perturbations allowing us to confront them with the observation of the Cosmic Microwave Background and Large Scale Structure and demonstrate how it is possible in principle to reconstruct the equation of state of dark energy by also using Supernovae Ia observational data. We also discuss in detail the nature of tracking solutions in cosmology, particle physics and braneworld models of dark energy, the nature of possible future singularities, the effect of higher order curvature terms to avoid a Big Rip singularity, and approaches to modifying gravity which leads to a late-time accelerated expansion without recourse to a new form of dark energy.

- by Muhammad Sami
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- Mathematical Physics, Quantum Physics, Particle Physics, Dark Energy

In 'The Hitchhiker's Guide to the Galaxy', by Douglas Adams, the Answer to the Ultimate Question of Life, the Universe, and Everything is found to be 42 { but
the meaning of this is left open to interpretation. We take it to mean that there are 42
fundamental questions which must be answered on the road to full enlightenment, and we attempt a first draft (or personal selection) of these ultimate questions, on topics ranging from the cosmological constant and origin of the universe to the origin of life and consciousness.

- by Suzy Lidström
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- Quantum Gravity, Quantum Chromodynamics, Consciousness, Cosmic Inflation

We review the paradigm of quintom cosmology. This scenario is motivated by the observational indications that the equation of state of dark energy across the cosmological constant boundary is mildly favored, although the data are still far from being conclusive. As a theoretical setup we introduce a no-go theorem existing in quintom cosmology, and based on it we discuss the conditions for the equation of state of dark energy realizing the quintom scenario. The simplest quintom model can be achieved by introducing two scalar fields with one being quintessence and the other phantom. Based on the double-field quintom model we perform a detailed analysis of dark energy perturbations and we discuss their effects on current observations. This type of scenarios usually suffer from a manifest problem due to the existence of a ghost degree of freedom, and thus we review various alternative realizations of the quintom paradigm. The developments in particle physics and string theory provide potential clues indicating that a quintom scenario may be obtained from scalar systems with higher derivative terms, as well as from nonscalar systems. Additionally, we construct a quintom realization in the framework of braneworld cosmology, where the cosmic acceleration and the phantom divide crossing result from the combined effects of the field evolution on the brane and the competition between four and five dimensional gravity. Finally, we study the outsets and fates of a universe in quintom cosmology. In a scenario with null energy condition violation one may obtain a bouncing solution at early times and therefore avoid the Big Bang singularity. Furthermore, if this occurs periodically, we obtain a realization of an oscillating universe. Lastly, we comment on several open issues in quintom cosmology and their connection to future investigations.

- by S. Simonucci
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- Particle Physics, String Theory, Dark Energy, Big Bang

We discuss the theory of knots, and describe how knot invariants arise naturally in gravitational physics. The focus of this review is to delineate the relationship between knot theory and the loop representation of non-perturbative canonical quantum general relativity (loop quantum gravity). This leads naturally to a discussion of the Kodama wavefunction, a state which is conjectured to be the ground state of the gravitational field with positive cosmological constant. This review can serve as a self-contained introduction to loop quantum gravity and related areas. Our intent is to make the paper accessible to a wider audience that may include topologists, knot-theorists, and other persons innocent of the physical background to this approach to quantum gravity.

- by Louis H Kauffman
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- Quantum Gravity, General Relativity, Knot Theory, Loop Quantum Gravity

First, the ideas introduced in the wormhole research field since the work of Morris and Thorne are reviewed, namely, the issues of energy conditions, wormhole construction, stability, time machines and astrophysical signatures. Then, spherically symmetric and static traversable Morris -Thorne wormholes in the presence of a generic cosmological constant Λ are analyzed. A matching of an interior solution to the unique exterior vacuum solution is done using directly the Einstein equations. The structure as well as several physical properties and characteristics of traversable wormholes due to the effects of the cosmological term are studied. Interesting equations appear in the process of matching. For instance, one finds that for asymptotically flat and anti-de Sitter spacetimes the surface tangential pressure P of the thin shell, at the boundary of the interior and exterior solutions, is always strictly positive, whereas for de Sitter spacetime it can take either sign as one could expect, being negative (tension) for relatively high Λ and high wormhole radius, positive for relatively high mass and small wormhole radius, and zero in-between. Finally, some specific solutions with Λ, based on the Morris -Thorne solutions, are provided.

- by Francisco Lobo
- •
- Quantum Physics, Cosmological Constant, Physical Properties

Recent observations of Type 1a supernovae indicating an accelerating universe have once more drawn attention to the possible existence, at the present epoch, of a small positive Λ-term (cosmological constant). In this paper we review both observational and theoretical aspects of a small cosmological Λ-term. We discuss the current observational situation focusing on cosmological tests of Λ including the age of the universe, high redshift supernovae, gravitational lensing, galaxy clustering and the cosmic microwave background. We also review the theoretical debate surrounding Λ: the generation of Λ in models with spontaneous symmetry breaking and through quantum vacuum polarization effects -mechanisms which are known to give rise to a large value of Λ hence leading to the 'cosmological constant problem'. More recent attempts to generate a small cosmological constant at the present epoch using either field theoretic techniques, or by modeling a dynamical Λ-term by scalar fields are also extensively discussed. Anthropic arguments favouring a small Λ-term are briefly reviewed. A comprehensive bibliography of recent work on Λ is provided.

- by A. Starobinsky
- •
- Mathematical Physics, Quantum Physics, Quantum Vacuum, Cosmic Microwave Background

Theoretical approaches to explaining the observed acceleration of the universe are reviewed. We briefly discuss the evidence for cosmic acceleration, and the implications for standard General Relativity coupled to conventional sources of energy-momentum. We then address three broad methods of addressing an accelerating universe: the introduction of a cosmological constant, its problems and origins; the possibility of dark energy, and the associated challenges for fundamental physics; and the option that an infrared modification of general relativity may be responsible for the large-scale behavior of the universe.

- by Mark Trodden
- •
- General Relativity, Dark Energy, Mathematical Sciences, Physical sciences

A proposal is made for a cosmological D3/D7 model with a constant magnetic flux along the D7 world-volume. It describes an N = 2 gauge model with Fayet-Iliopoulos terms and the potential of the hybrid P-term inflation. The motion of the D3-brane towards D7 in a phase with spontaneously broken supersymmetry provides a period of slow-roll inflation in the de Sitter valley, the role of the inflaton being played by the distance between D3 and D7-branes. After tachyon condensation a supersymmetric ground state is formed: a D3/D7 bound state corresponding to an Abelian non-linear (non-commutative) instanton. In this model the existence of a non-vanishing cosmological constant is associated with the resolution of the instanton singularity. We discuss a possible embedding of this model into a compactified M-theory setup. 1

- by Carlos Herdeiro
- •
- Field Theory, Quantum Physics, Early Universe, Non-commutative Geometry

We present a reformulation of loop quantum gravity with a cosmological constant and no matter as a Fermi-liquid theory. When the topological sector is deformed and large gauge symmetry is broken, we show that the Chern-Simons state reduces to Jacobson's degenerate sector describing 1 + 1 dimensional propagating fermions with nonlocal interactions. The Hamiltonian admits a dual description which we realize in the simple BCS model of superconductivity. On one hand, Cooper pairs are interpreted as wormhole correlations at the de Sitter horizon; their number yields the de Sitter entropy. On the other hand, BCS is mapped into a deformed conformal field theory reproducing the structure of quantum spin networks. When area measurements are performed, Cooper-pair insertions are activated on those edges of the spin network intersecting the given area, thus providing a description of quantum measurements in terms of excitations of a Fermi sea to superconducting levels. The cosmological constant problem is naturally addressed as a nonperturbative mass-gap effect of the true Fermi-liquid vacuum. (Gianluca Calcagni). arXiv:0807.0225 [hep-th] Found. Phys. 3 This means that [Ĉ i ,Ĉ j ] =Ô k ijĈ k , whereĈ i are the Hamiltonian, Gauss, and vector constraints andÔ is an operator defining the structure coefficients of the algebra. 4 See in particular Exercise 3.7 in [17], p. 258.

In this work we address the study of null geodesics in the background of Reissner-Nordstr\"om Anti de Sitter black holes. We compute the exact trajectories in terms of elliptic functions of Weierstrass, obtaining a detailed description of the orbits in terms of charge, mass and the cosmological constant. The trajectories of the photon are classified using the impact parameter.

- by Norman Cruz
- •
- Quantum Cosmology, High Energy Physics, Black Hole, Cosmological Constant

We use a series of ray-tracing experiments to determine the magnification distribution of high-redshift sources by gravitational lensing. We determine empirically the relation between magnification and redshift, for various cosmological models. We then use this relation to estimate the effect of lensing on the determination of the cosmological parameters from observations of high-z supernovae. We found that, for supernovae at redshifts z < 1.8, the effect of lensing is negligible compared to the intrinsic uncertainty in the measurements. Using mock data in the range 1.8 < z < 8, we show that the effect of lensing can become significant. Hence, if a population of very-high-z supernovae was ever discovered, it would be crucial to fully understand the effect of lensing, before these SNe could be used to constrain cosmological models. We show that the distance moduli m−M for an open CDM universe and a ΛCDM universe are comparable at z > 2. Therefore if supernovae up to these redshifts were ever discovered, it is still the ones in the range 0.3 < z < 1 that would distinguish these two models.

Several kinds of astronomical observations, interpreted in the framework of the standard Friedmann-Robertson-Walker cosmology, have indicated that our universe is dominated by a Cosmological Constant. The dimming of distant Type Ia supernovae suggests that the expansion rate is accelerating, as if driven by vacuum energy, and this has been indirectly substantiated through studies of angular anisotropies in the cosmic microwave background (CMB) and of spatial correlations in the large-scale structure (LSS) of galaxies. However there is no compelling direct evidence yet for (the dynamical effects of) dark energy. The precision CMB data can be equally well fitted without dark energy if the spectrum of primordial density fluctuations is not quite scale-free and if the Hubble constant is lower globally than its locally measured value. The LSS data can also be satisfactorily fitted if there is a small component of hot dark matter, as would be provided by neutrinos of mass ∼ 0.5 eV. Although such an Einstein-de Sitter model cannot explain the SNe Ia Hubble diagram or the position of the 'baryon acoustic oscillation' peak in the autocorrelation function of galaxies, it may be possible to do so e.g. in an inhomogeneous Lemaitre-Tolman-Bondi cosmology where we are located in a void which is expanding faster than the average. Such alternatives may seem contrived but this must be weighed against our lack of any fundamental understanding of the inferred tiny energy scale of the dark energy. It may well be an artifact of an oversimplified cosmological model, rather than having physical reality.

- by Subir Sarkar
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- Mathematical Physics, Quantum Physics, Dark Energy, Cosmic Microwave Background

- by Muhammad Sami
- •
- Mathematical Physics, Quantum Physics, Particle Physics, Dark Energy

We construct static codimension-two branes in any odd dimension D, with negative cosmological constant, and show that they are exact solutions of Chern-Simons (super)gravity theory for (super)AdS D coupled to external sources. The stability of these solutions is analyzed by counting the number of preserved supersymmetries. It is shown that static massive (D − 3)-branes are unstable unless some suitable gauge fields are added and the brane is extremal. In particular, in three dimensions, a 0-brane is recognized as the negative mass counterpart of the BTZ black hole. For these 0-branes, we write explicitly magnetically charged BPS states with various number of preserved supersymmetries within the OSp(p|2) × OSp(q|2) supergroups. In five dimensions, we prove that stable 2-branes with magnetic charge always exist for the generic supergroup SU (2, 4|N ), where N = 4. For the special case N = 4, in which the CS supergravity requires the addition of a nontrivial gauge field configuration in order to preserve maximal number of degrees of freedom, we show for two different static 2-branes that they are BPS states (one of which is the ground state), and from the corresponding algebra of charges we show that the energy is bounded from below. In higher dimensions, our results admit a straightforward generalization, although there are presumably more solutions corresponding to different intersections of the elementary objects.

- by Olivera Mišković and +1
- •
- Quantum Physics, Black Hole, Cosmological Constant, Chern Simons Theory

In this work we construct and analyze exact solutions describing Ricci flows and nonholonomic deformations of four dimensional (4D) Taub-NUT spacetimes. It is outlined a new geometric techniques of constructing Ricci flow solutions. Some conceptual issues on spacetimes provided with generic off-diagonal metrics and associated nonlinear connection structures are analyzed. The limit from gravity/Ricci flow models with nontrivial torsion to configurations with the Levi-Civita connection is allowed in some specific physical circumstances by constraining the class of integral varieties for the Einstein and Ricci flow equations.

- by Sergiu Vacaru
- •
- Quantum Cosmology, High Energy Physics, Differential Geometry, Unified Field Theory

We consider the Universe deep inside the cell of uniformity. At these scales, the Universe is filled with inhomogeneously distributed discrete structures (galaxies, groups and clusters of galaxies), which perturb the background Friedmann model. Here, the mechanical approach (Eingorn & Zhuk, 2012) is the most appropriate to describe the dynamics of the inhomogeneities which is defined, on the one hand, by gravitational potentials of inhomogeneities and, on the other hand, by the cosmological expansion of the Universe. In this paper, we present additional arguments in favor of this approach. First, we estimate the size of the cell of uniformity. With the help of the standard methods of statistical physics and for the galaxies of the type of the Milky Way and Andromeda, we get that it is of the order of 190 Mpc which is rather close to observations. Then, we show that the nonrelativistic approximation (with respect to the peculiar velocities) is valid for zlesssim10z \lesssim 10zlesssim10, i.e. approximately for 13 billion years from the present moment. We consider scalar perturbations and, within the Lambda\LambdaLambdaCDM model, justify the main equations. Moreover, we demonstrate that radiation can be naturally incorporated into our scheme. This emphasizes the viability of our approach. This approach gives a possibility to analyze different cosmological models and compare them with the observable Universe. For example, we indicate some problematic aspects of the spatially flat models. Such models require a rather specific distribution of the inhomogeneities to get a finite potential at any points outside gravitating masses. We also criticize the application of the Schwarzschild-de Sitter solution to the description of the motion of test bodies on the cosmological background.

- by Maxim Eingorn
- •
- Mathematical Physics, Geometry And Topology, Physics, Theoretical Physics

The theory of massive gravity in three dimensions recently proposed by Bergshoeff, Hohm and Townsend (BHT) is considered. At the special case when the theory admits a unique maximally symmetric solution, a conformally flat space that contains black holes and gravitational solitons for any value of the cosmological constant is found. For negative cosmological constant, the black hole is characterized in terms of the mass and the "gravitational hair" parameter, providing a lower bound for the mass. For negative mass parameter, the black hole acquires an inner horizon, and the entropy vanishes at the extremal case. Gravitational solitons and kinks, being regular everywhere, are obtained from a double Wick rotation of the black hole. A wormhole solution in vacuum that interpolates between two static universes of negative spatial curvature is obtained as a limiting case of the gravitational soliton with a suitable identification. The black hole and the gravitational soliton fit within a set of relaxed asymptotically AdS conditions as compared with the ones of Brown and Henneaux. In the case of positive cosmological constant the black hole possesses an event and a cosmological horizon, whose mass is bounded from above. Remarkably, the temperatures of the event and the cosmological horizons coincide, and at the extremal case one obtains the analogue of the Nariai solution, dS2timesS1dS_{2}\times S^{1}dS2timesS1. A gravitational soliton is also obtained through a double Wick rotation of the black hole. The Euclidean continuation of these solutions describes instantons with vanishing Euclidean action. For vanishing cosmological constant the black hole and the gravitational soliton are asymptotically locally flat spacetimes. The rotating solutions can be obtained by boosting the previous ones in the t−phit-\phit−phi plane.

- by Julio Oliva
- •
- High Energy Physics, Mathematical Sciences, Physical sciences, Black Hole

In this paper, (part VI) we analyze further equations of Manuscript Book 2 of Srinivasa Ramanujan. We describe the new possible mathematical connections with the MRB (Marvin Ray Burns) Constant and several equations concerning some... more

- by Michele Nardelli
- •
- Number Theory, String Theory, Black Hole Physics, Supersymmetry breaking
- by Øyvind Grøn
- •
- Quantum Cosmology, Magnetic field, Cosmological Constant, Lorentz Invariance