scholarly journals ACCELERATION OF THE UNIVERSE IN TYPE-0 NONCRITICAL STRINGS

2002 ◽  
Vol 17 (30) ◽  
pp. 4567-4589 ◽  
Author(s):  
G. A. DIAMANDIS ◽  
B. C. GEORGALAS ◽  
N. E. MAVROMATOS ◽  
E. PAPANTONOPOULOS
Keyword(s):  
String Theory ◽  
Extra Dimensions ◽  
Scattering Matrix ◽  
Relative Magnitude ◽  
Observational Evidence ◽  
De Sitter ◽  
Brane Worlds ◽  
Acceleration Of The Universe ◽  
Noncritical Strings ◽  
The Universe

Presently there is preliminary observational evidence that the cosmological constant might be nonzero, and hence that our universe is eternally accelerating (de Sitter). This poses fundamental problems for string theory, since a scattering matrix is not well defined in such universes. In a previous paper we have presented a model, based on (nonequilibrium) noncritical strings, which is characterized by eventual "graceful" exit from a de Sitter phase. The model is based on a type-0 string theory, involving D3 brane worlds, whose initial quantum fluctuations induce the noncriticality. We argue in this paper that this model is compatible with the current observations. A crucial role for the correct "phenomenology" of the model is played by the relative magnitude of the flux of the five-form of the type 0 string to the size of five of the extra dimensions, transverse to the direction of the flux-field. We do not claim, at this stage at least, that this model is a realistic physical model for the universe, but we find it interesting that the model cannot be ruled out immediately, at least on phenomenological grounds.

DARK GEOMETRY

2004 ◽  
Vol 13 (10) ◽  
pp. 2275-2279 ◽  
Author(s):  
J. A. R. CEMBRANOS ◽  
A. DOBADO ◽  
A. L. MAROTO
Keyword(s):  
Dark Matter ◽  
Extra Dimensions ◽  
Degrees Of Freedom ◽  
Planck Scale ◽  
Point Of View ◽  
Missing Mass ◽  
Brane Worlds ◽  
Mass Problem ◽  
Extra Space ◽  
The Universe

Extra-dimensional theories contain additional degrees of freedom related to the geometry of the extra space which can be interpreted as new particles. Such theories allow to reformulate most of the fundamental problems of physics from a completely different point of view. In this essay, we concentrate on the brane fluctuations which are present in brane-worlds, and how such oscillations of the own space–time geometry along curved extra dimensions can help to resolve the Universe missing mass problem. The energy scales involved in these models are low compared to the Planck scale, and this means that some of the brane fluctuations distinctive signals could be detected in future colliders and in direct or indirect dark matter searches.

Cosmic acceleration with tachyon field

2018 ◽  
Vol 33 (34) ◽  
pp. 1850199 ◽  
Author(s):  
A. I. Keskin
Keyword(s):  
Scalar Field ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Cosmic Acceleration ◽  
Late Time ◽  
De Sitter ◽  
Tachyon Field ◽  
Minimal Coupling ◽  
Acceleration Of The Universe ◽  
The Universe

In this study, we examine two models of the scalar field, that is, a normal scalar field and a tachyon scalar field in [Formula: see text] gravity to describe cosmic acceleration of the universe, where [Formula: see text], [Formula: see text] and [Formula: see text] are Ricci curvature scalar, trace of energy–momentum tensor and kinetic energy of scalar field [Formula: see text], respectively. Using the minimal-coupling Lagrangian [Formula: see text], for both the scalar models we obtain a viable cosmological system, where [Formula: see text] and [Formula: see text] are real constants. While a normal scalar field gives a system describing expansion from the deceleration to the late-time acceleration, tachyon field together with [Formula: see text] in the system produces a quintessential expansion which is very close to de Sitter point, where we find a new condition [Formula: see text] for inflation.

scholarly journals Hybrid inflation and waterfall field in string theory from D7-branes

2022 ◽  
Vol 2022 (1) ◽  
Author(s):  
Ignatios Antoniadis ◽  
Osmin Lacombe ◽  
George K. Leontaris
Keyword(s):  
String Theory ◽  
Flux Compactifications ◽  
Saddle Point ◽  
Present State ◽  
Global Minimum ◽  
Vacuum Energy ◽  
De Sitter ◽  
Hybrid Inflation ◽  
De Sitter Vacuum ◽  
The Universe

Abstract We present an explicit string realisation of a cosmological inflationary scenario we proposed recently within the framework of type IIB flux compactifications in the presence of three magnetised D7-brane stacks. Inflation takes place around a metastable de Sitter vacuum. The inflaton is identified with the volume modulus and has a potential with a very shallow minimum near the maximum. Inflation ends due to the presence of “waterfall” fields that drive the evolution of the Universe from a nearby saddle point towards a global minimum with tuneable vacuum energy describing the present state of our Universe.

scholarly journals WE PROBABLY LIVE ON AN INFLATING BRANE-WORLD

2011 ◽  
Vol 20 (14) ◽  
pp. 2809-2816
Author(s):  
ISHWAREE P. NEUPANE
Keyword(s):  
Zero Mode ◽  
De Sitter Space ◽  
Brane World ◽  
Conformal Field Theories ◽  
De Sitter ◽  
Conformal Field ◽  
Sitter Spacetime ◽  
Acceleration Of The Universe ◽  
De Sitter Universe ◽  
The Universe

Brane-world models, where observers are trapped within the thickness of a 3-brane, offer novel perspectives on gravitation and cosmology. In this essay, it is argued that the problem of a late epoch acceleration of the universe is well explained in the framework of a 4-dimensional de Sitter universe embedded in a 5-dimensional de Sitter spacetime. While a 5-dimensional Anti-de Sitter space background is important for studying conformal field theories for its role in the AdS/CFT correspondence, the existence of a 5-dimensional de Sitter space is crucial for finding an effective 4-dimensional Newton constant that remains finite and a normalizable zero-mode graviton wave function.

scholarly journals GENERALIZED PARTICLE DYNAMICS IN ANTI-DE SITTER SPACES: A SOURCE FOR DARK ENERGY

2011 ◽  
Vol 20 (07) ◽  
pp. 1235-1249 ◽  
Author(s):  
SUDIPTA DAS ◽  
SUBIR GHOSH ◽  
JAN-WILLEM VAN HOLTEN ◽  
SUPRATIK PAL
Keyword(s):  
Dark Energy ◽  
Energy Equation ◽  
Cosmological Parameters ◽  
High Energy ◽  
Particle Dynamics ◽  
De Sitter ◽  
Acceleration Of The Universe ◽  
Sitter Background ◽  
Flrw Universe ◽  
The Universe

We consider the generalized particle dynamics, that we proposed [S. Das et al., J. High. Energy Phys.0904 (2009) 115] in braneworld formalisms for an asymptotically anti-de Sitter background. The present framework results in a new model that accounts for the late acceleration of the universe. An effective dark energy equation of state, exhibiting a phantom-like behavior, is generated. The model is derived by embedding the physical FLRW universe in a (4 + 1)-dimensional effective spacetime, induced by the generalized particle dynamics. We corroborate our results with present-day observed cosmological parameters.

scholarly journals The acceleration of the universe, a challenge for string theory

2001 ◽  
Vol 2001 (07) ◽  
pp. 003-003 ◽  
Author(s):  
Willy Fischler ◽  
Amir Kashani-Poor ◽  
Robert McNees ◽  
Sonia Paban
Keyword(s):  
String Theory ◽  
Acceleration Of The Universe ◽  
The Universe

scholarly journals Generalized holographic cosmology: low-redshift observational constraint

2021 ◽  
Vol 2021 (10) ◽  
Author(s):  
Sunly Khimphun ◽  
Bum-Hoon Lee ◽  
Gansukh Tumurtushaa
Keyword(s):  
Black Hole ◽  
Observational Data ◽  
Information Criterion ◽  
Current Data ◽  
Late Time ◽  
De Sitter ◽  
Λcdm Model ◽  
Acceleration Of The Universe ◽  
The Universe ◽  
Friedmann Robertson Walker

Abstract Four-dimensional cosmological models are studied on a boundary of a five-dimensional Anti-de Sitter (AdS5) black hole with AdS Reissner-Nordström and scalar charged Reissner-Nordström black hole solutions, where we call the former a “Hairless” black hole and the latter a “Hairy” black hole. To obtain the Friedmann-Robertson-Walker (FRW) spacetime metric on the boundary of the AdS5 black hole, we employ Eddington-Finkelstein (EF) coordinates to the bulk geometry. We then derive modified Friedmann equations on a boundary of the AdS5 black hole via AdS/CFT correspondence and discuss its cosmological implications. The late-time acceleration of the universe is investigated in our models. The contributions coming from the bulk side is treated as dark energy source, and we perform MCMC analyses using observational data. Compared to the ΛCDM model, our models contain additional free parameters; therefore, to make a fair comparison, we use the Akaike information criterion (AIC) and the Bayesian information criterion (BIC) to analyze our results. Our numerical analyses show that our models can explain the observational data as reliable as the ΛCDM model does for the current data.

scholarly journals Late transient acceleration of the universe in string theory onS1/Z2

2008 ◽  
Vol 2008 (09) ◽  
pp. 004 ◽  
Author(s):  
Qiang Wu ◽  
N O Santos ◽  
Pamela Vo ◽  
Anzhong Wang
Keyword(s):  
String Theory ◽  
Acceleration Of The Universe ◽  
The Universe

SELF-CREATING BRANE WORLDS

2004 ◽  
Vol 13 (01) ◽  
pp. 85-106 ◽  
Author(s):  
PEDRO F. GONZÁLEZ-DÍAZ ◽  
JUAN MARTÍN CARRIÓN
Keyword(s):  
Quantum Theory ◽  
Boundary Conditions ◽  
Quantum State ◽  
De Sitter Space ◽  
De Sitter ◽  
Brane Worlds ◽  
Multiply Connected ◽  
Spacetime Structure ◽  
Multiply Connected Region ◽  
The Universe

Several boundary conditions for the universe have been hitherto suggested, basing on different philosophical approaches. In particular, one may choose between the notions that the universe was created either from nothing or by itself. The quantum state of a universe created from nothing has been already formulated under distinct standpoints by Hartle, Hawking, Vilenkin and others. In this paper we have concentrated on deriving a quantum theory for a self-created universe. Thus, we have first considered the spacetime structure of a six-dimensional de Sitter space with a multiply connected region and, by using a cutting and pasting procedure, we have then been able to show that one can introduce a four-brane in such a spacetime whose evolution can also be considered within the context of ekpyrotic and cyclic universes, and quantized in terms of the sum-over-histories formulation, according to the rules of the generalized quantum theory developed by Hartle.

Sign in / Sign up

Export Citation Format

Share Document