scholarly journals Phantom wormhole solutions in a generic cosmological constant background

2015 ◽  
Vol 93 (12) ◽  
pp. 1523-1531 ◽  
Author(s):  
Y. Heydarzade ◽  
N. Riazi ◽  
H. Moradpour
Keyword(s):  
Cosmological Constant ◽  
Energy Condition ◽  
State Parameter ◽  
Pressure Profile ◽  
Mass Function ◽  
Specific Class ◽  
Accelerating Expansion ◽  
Expansion Of The Universe ◽  
Metric Functions ◽  
Superstring Theories

There are a number of reasons to study wormholes with generic cosmological constant Λ. Recent observations indicate that the present accelerating expansion of the universe demands Λ > 0. On the other hand, some extended theories of gravitation, such as supergravity and superstring theories, possess vacuum states with Λ < 0. Even within the framework of general relativity, a negative cosmological constant permits black holes with horizons topologically different from the usual spherical ones. These solutions are convertible to wormhole solutions by adding some exotic matter. In this paper, the asymptotically flat wormhole solutions in a generic cosmological constant background are studied. By constructing a specific class of shape functions, a mass function, energy density, and pressure profile that support such a geometry are obtained. It is shown that for having such a geometry, the wormhole throat, r0, the cosmological constant, Λ, and the equation of state parameter, ω, should satisfy two specific conditions. The possibility of setting different values for the parameters of the model helps us to find exact solutions for the metric functions, mass functions, and energy–momentum profiles. At last, the volume integral quantifier, which provides useful information about the total amount of energy-condition violating matter, is discussed briefly.

scholarly journals PHANTOM COSMOLOGY WITH A NONLINEAR BORN–INFELD TYPE SCALAR FIELD

2005 ◽  
Vol 14 (02) ◽  
pp. 355-362 ◽  
Author(s):  
H. Q. LU
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Equation Of State ◽  
Energy Condition ◽  
State Parameter ◽  
Strong Energy Condition ◽  
Strong Energy ◽  
Accelerating Expansion ◽  
Equation Of State Parameter ◽  
The Universe

Recent many physicists suggest that the dark energy in the universe might result from the Born–Infeld (B–I) type scalar field of string theory. The universe of B–I type scalar field with potential can undergo a phase of accelerating expansion. The corresponding equation of state parameter lies in the range of -1<ω<-⅓. The equation of state parameter of B–I type scalar field without potential lies in the range of 0≤ω≤1. We find that weak energy condition and strong energy condition are violated for phantom B–I type scalar field. The equation of state parameter lies in the range of ω<-1.

scholarly journals THE EVOLUTION OF THE UNIVERSE WITH THE B–I TYPE PHANTOM SCALAR FIELD

2006 ◽  
Vol 15 (02) ◽  
pp. 199-214 ◽  
Author(s):  
WEI FANG ◽  
H. Q. LU ◽  
Z. G. HUANG ◽  
K. F. ZHANG
Keyword(s):  
Scalar Field ◽  
State Parameter ◽  
Phase Plane Analysis ◽  
Density Parameter ◽  
Late Time ◽  
Plane Analysis ◽  
Accelerating Expansion ◽  
Phantom Scalar ◽  
Expansion Of The Universe ◽  
The Universe

We consider the phantom cosmology with a Lagrangian [Formula: see text] originated from the nonlinear Born–Infeld type scalar field. This cosmological model can explain the accelerating expansion of the universe with the equation of state parameter w ≤ -1. We get a sufficient condition for an arbitrary potential that admits a late time attractor solution: the value of potential u(Xc) at the critical point (Xc, 0) should be maximum and greater than zero. We study a specific potential with the form of [Formula: see text] via phase plane analysis and compute the cosmological evolution by numerical analysis in detail. The results show that the phantom field survives till today (to account for the present observed accelerating expansion) without interfering with the nucleosynthesis of the standard model (the density parameter Ωϕ≃10-12 at the equipartition epoch), and also avoid the future collapse of the universe.

scholarly journals ADDRESSING THE CRISIS IN FUNDAMENTAL PHYSICS

2007 ◽  
Vol 16 (12a) ◽  
pp. 1947-1952
Author(s):  
CHRISTOPHER W. STUBBS
Keyword(s):  
Dark Energy ◽  
State Parameter ◽  
New Physics ◽  
Fundamental Physics ◽  
Accelerating Expansion ◽  
Cosmological Observations ◽  
Real Risk ◽  
Expansion Of The Universe ◽  
The One ◽  
The Universe

The observation that the expansion of the Universe is proceeding at an ever-increasing rate, i.e. the "dark energy" problem, constitutes a crisis in fundamental physics that is as profound as the one that preceded the advent of quantum mechanics. Cosmological observations currently favor a dark energy equation-of-state parameter w = P/ρ = -1. Awkwardly, this is the value that has the least ability to discriminate between alternatives for the physics that produces the observed accelerating expansion. If this result persists we therefore run a very real risk of stagnation in our attempt to better understand the nature of this new physics, unless we uncover another piece of the dark energy puzzle. I argue that precision fundamental measurements in space have an important role in addressing this crisis.

COSMOLOGY WITH NEGATIVE POTENTIALS WITH wϕ<-1

2004 ◽  
Vol 13 (09) ◽  
pp. 1939-1953 ◽  
Author(s):  
A. DE LA MACORRA ◽  
G. GERMÁN
Keyword(s):  
Equation Of State ◽  
Energy Density ◽  
Cosmological Constant ◽  
Particle Physics ◽  
Scalar Potential ◽  
Energy Condition ◽  
State Parameter ◽  
Scalar Fields ◽  
High Energy ◽  
Equation Of State Parameter

We study the cosmology of canonically normalized scalar fields that lead to an equation of state parameter of wϕ=pϕ/ρϕ<-1 without violating the weak energy condition: ρ=Σiρi≥0 and ρi+pi≥0. This kind of behavior requires a negative scalar potential V, widely predicted in particle physics. We show that the energy density ρϕ=Ek+V takes negative values with an equation of state with wϕ<-1. However, the net effect of the ϕ field on the scale factor is to decelerate it giving a total equation of state parameter w=p/ρ>wb=pb/ρb, where ρb stands for any kind of energy density with -1≤wb≤1, such as radiation, matter, cosmological constant or other scalar field with a potential V≥0. The fact that ρϕ<0 allows, at least in principle, to have a small cosmological constant or quintessence today as the cancellation of high energy scales such as the electroweak or susy breaking scale. While V is negative |ρϕ| is smaller than the sum of all other energy densities regardless of the functional form of the potential V. We show that the existence of a negative potential leads, inevitable, to a collapsing universe, i.e. to a would be "big crunch." In this picture we would still be living in the expanding universe.

scholarly journals Designer de Sitter spacetimes

2008 ◽  
Vol 86 (4) ◽  
pp. 591-595
Author(s):  
K Schleich ◽  
D M Witt
Keyword(s):  
Cosmological Constant ◽  
Infinite Family ◽  
Einstein Equations ◽  
Global Dynamics ◽  
De Sitter Spacetime ◽  
De Sitter ◽  
Isotropic Solution ◽  
Accelerating Expansion ◽  
Sitter Spacetime ◽  
Expansion Of The Universe

Recent observations in cosmology indicate an accelerating expansion of the Universe postulated to arise from some form of dark energy, the paradigm being positive cosmological constant. De Sitter spacetime is the well-known isotropic solution to the Einstein equations with cosmological constant. However, as discussed here, it is not the most general, locally isotropic solution. One can construct an infinite family of such solutions, designer de Sitter spacetimes, which are everywhere locally isometric to a region of de Sitter spacetime. However, the global dynamics of these designer cosmologies is very different than that of de Sitter spacetime itself. The construction and dynamics of these designer de Sitter spacetimes is detailed along with some comments about their implications for the structure of our Universe.PACS Nos.: 04.20.–q, 04.20.Ex, 04.20.Gz, 98.80.–k

scholarly journals Dimensional reduction and (Anti) de Sitter bounds

2021 ◽  
Vol 2021 (8) ◽  
Author(s):  
Tom Rudelius
Keyword(s):  
Scalar Field ◽  
Cosmological Constant ◽  
Dimensional Reduction ◽  
Energy Condition ◽  
Field Potential ◽  
Limited Range ◽  
Mass Scale ◽  
Accelerated Expansion ◽  
De Sitter ◽  
Expansion Of The Universe

Abstract Dimensional reduction has proven to be a surprisingly powerful tool for delineating the boundary between the string landscape and the swampland. Bounds from the Weak Gravity Conjecture and the Repulsive Force Conjecture, for instance, are exactly preserved under dimensional reduction. Motivated by its success in these cases, we apply a similar dimensional reduction analysis to bounds on the gradient of the scalar field potential V and the mass scale m of a tower of light particles in terms of the cosmological constant Λ, which ideally may pin down ambiguous O(1) constants appearing in the de Sitter Conjecture and the (Anti) de Sitter Distance Conjecture, respectively. We find that this analysis distinguishes the bounds $$ \left|\nabla V\right|/V\ge \sqrt{4/\left(d-2\right)} $$ ∇ V / V ≥ 4 / d − 2 , m ≲ |Λ|1/2, and m ≲ |Λ|1/d in d-dimensional Planck units. The first of these bounds is equivalent to the strong energy condition in Einstein-dilaton gravity and precludes accelerated expansion of the universe. It is almost certainly violated in our universe, though it may apply in asymptotic limits of scalar field space. The second bound cannot be satisfied in our universe, though it is saturated in supersymmetric AdS vacua with well-understood uplifts to 10d/11d supergravity. The third bound likely has a limited range of validity in quantum gravity as well, so it may or may not apply to our universe. However, if it does apply, it suggests a possible relation between the cosmological constant and the neutrino mass, which (by the see-saw mechanism) may further provide a relation between the cosmological constant problem and the hierarchy problem. We also work out the conditions for eternal inflation in general spacetime dimensions, and we comment on the behavior of these conditions under dimensional reduction.

scholarly journals Does holographic equipartition demand a pure cosmological constant?

2020 ◽  
pp. 2050334
Author(s):  
P. B. Krishna ◽  
Titus K. Mathew
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Dark Energy Model ◽  
State Parameter ◽  
De Sitter ◽  
Entropy Maximization ◽  
Expansion Of The Universe ◽  
The Law ◽  
De Sitter Universe ◽  
The Universe

The spacial expansion of the universe could be described as a tendency for satisfying holographic equipartition which inevitably demands the presence of dark energy. We explore whether this novel idea proposed by Padmanabhan gives any additional insights into the nature of dark energy. In particular, we obtain the constraints imposed by the law of emergence on the equation of state parameter, [Formula: see text]. We also present a thermodynamic motivation for the obtained constraints on [Formula: see text]. Further, we explicitly prove the feasibility of describing a dynamic dark energy model through the law of emergence. Interestingly, both holographic equipartition and the entropy maximization demand an asymptotically de Sitter universe with [Formula: see text], rather than a pure cosmological constant.

scholarly journals Vacuum energy and the cosmological constant

2015 ◽  
Vol 30 (22) ◽  
pp. 1540033 ◽  
Author(s):  
Steven D. Bass
Keyword(s):  
Energy Density ◽  
Large Hadron Collider ◽  
Cosmological Constant ◽  
Vacuum Energy ◽  
Hadron Collider ◽  
Planck Scale ◽  
Vacuum Energy Density ◽  
Accelerating Expansion ◽  
Expansion Of The Universe ◽  
The Universe

The accelerating expansion of the Universe points to a small positive value for the cosmological constant or vacuum energy density. We discuss recent ideas that the cosmological constant plus Large Hadron Collider (LHC) results might hint at critical phenomena near the Planck scale.

scholarly journals Accelerating universe in modified teleparallel gravity theory

2019 ◽  
Vol 15 (S356) ◽  
pp. 397-399
Author(s):  
Shambel Sahlu ◽  
Joseph Ntahompagaze ◽  
Amare Abebe ◽  
David F. Mota
Keyword(s):  
State Parameter ◽  
Teleparallel Gravity ◽  
Gravity Theory ◽  
Gravity Models ◽  
Accelerating Universe ◽  
Late Time ◽  
Numerical Result ◽  
Accelerating Expansion ◽  
Expansion Of The Universe ◽  
The Universe

AbstractThis paper studies the cosmology of accelerating expansion of the universe in modified teleparallel gravity theory. We discuss the cosmology of f(T, B) gravity theory and its implication to the new general form of the equation of state parameter wTB for explaining the late-time accelerating expansion of the universe without the need for the cosmological constant scenario. We examine the numerical value of wTB in different paradigmatic f(T, B) gravity models. In those models, the numerical result of wTB is favored with observations in the presence of the torsion scalar T associated with a boundary term B and shows the accelerating expansion of the universe.

scholarly journals EXPLAINING THE SUPERNOVA DATA WITHOUT ACCELERATING EXPANSION

2012 ◽  
Vol 21 (11) ◽  
pp. 1242021 ◽  
Author(s):  
W. M. STUCKEY ◽  
T. J. McDEVITT ◽  
M. SILBERSTEIN
Keyword(s):  
General Relativity ◽  
Quantum Gravity ◽  
Cosmological Constant ◽  
Nobel Prize ◽  
De Sitter ◽  
Accelerating Expansion ◽  
Type Ia ◽  
Expansion Of The Universe ◽  
Nobel Prize In Physics ◽  
The Universe

The 2011 Nobel Prize in Physics was awarded "for the discovery of the accelerating expansion of the universe through observations of distant supernovae." However, it is not the case that the type Ia supernova data necessitates accelerating expansion. Since we do not have a successful theory of quantum gravity, we should not assume general relativity (GR) will survive unification intact, especially on cosmological scales where tests are scarce. We provide a simple example of how GR cosmology may be modified to produce a decelerating Einstein-de Sitter cosmology (EdS) that accounts for the Union2 Compilation data as well as the accelerating ΛCDM (EdS plus a cosmological constant).

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