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Braneworld Gravity: Influence of the Moduli Fields
, 2000
"... We consider the case of a generic braneworld geometry in the presence of one or more moduli fields (e.g., the dilaton) that vary throughout the bulk spacetime. Working in an arbitrary conformal frame, using the generalized junction conditions of grqc/0008008 and the Gauss–Codazzi equations, we deri ..."
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We consider the case of a generic braneworld geometry in the presence of one or more moduli fields (e.g., the dilaton) that vary throughout the bulk spacetime. Working in an arbitrary conformal frame, using the generalized junction conditions of grqc/0008008 and the Gauss–Codazzi equations, we derive the effective “induced ” onbrane gravitational equations. As usual in braneworld scenarios, these equations do not form a closed system in that the bulk can exchange both information and stressenergy with the braneworld. We work with an arbitrary number of moduli fields described by an arbitrary sigma model, with arbitrary curvature couplings, arbitrary self interactions, and arbitrary dimension for the bulk. (The braneworld is always codimension one.) Among the novelties we encounter are modifications of the onbrane stressenergy conservation law, anomalous couplings between onbrane gravity and the trace of the onbrane stressenergy tensor, and additional possibilities for modifying the onbrane effective cosmological constant. After obtaining the general stressenergy “conservation ” law and the “induced Einstein equations ” we particularize the discussion to two particularly attractive cases: for a (n–2)brane in ([n–1]+1) dimensions we discuss both the effect of (1) generic variable moduli fields in the Einstein frame, and (2) the effect of a varying dilaton in the string frame.
BraneWorld charges
"... As opposed to usual Einstein gravity in four dimensions, the BraneWorld scenario allows the construction of a local density of gravitational energy (and also of momentum, of angular momentum, etc...). This is a direct consequence of the hypothesis that our universe is located at the boundary of a f ..."
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As opposed to usual Einstein gravity in four dimensions, the BraneWorld scenario allows the construction of a local density of gravitational energy (and also of momentum, of angular momentum, etc...). This is a direct consequence of the hypothesis that our universe is located at the boundary of a fivedimensional diffeomorphism invariant manifold. We compute these BraneWorld densities of charge using the LanczosIsrael boundary conditions. To proceed, we implement an explicitely covariant generalization of the Hamiltonian procedure of Regge and Teitelboim given in a previous work. We finally study two simple BraneWorld examples. 1 The idea that our fourdimensional universe could be the boundary of a fivedimensional spacetime has been recently revived as an alternative to KaluzaKlein compactification [1]. The classical theory in the bulk is nothing but
THE COSMOLOGICAL CONSTANT AND THE BRANE WORLD SCENARIO ∗
, 2001
"... Although the cosmological constant has primarily cosmological consequences, its smallness poses one of the basic problems in particle physics. Various attempts have been made to explain this mystery, but no satisfactory solution has been found yet. The appearance of extra dimensions in the framework ..."
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Although the cosmological constant has primarily cosmological consequences, its smallness poses one of the basic problems in particle physics. Various attempts have been made to explain this mystery, but no satisfactory solution has been found yet. The appearance of extra dimensions in the framework of brane world systems seems to provide some new ideas to address this problem form a different point of view. We shall discuss some of these new approaches and see whether or not they lead to an improvement of the situation. We shall conclude that we are still far from a solution of the problem. 1
Holographic Cosmic Quintessence on Dilatonic Brane
, 2001
"... Recently quintessence is proposed to explain the observation data of supernova indicating a timevarying cosmological constant and accelerating universe. Inspired by this and its mysterious origin, we look for the possibility of quintessence as the holographic dark matters dominated in the late time ..."
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Recently quintessence is proposed to explain the observation data of supernova indicating a timevarying cosmological constant and accelerating universe. Inspired by this and its mysterious origin, we look for the possibility of quintessence as the holographic dark matters dominated in the late time in the brane world scenarios. We consider both the cases of static and moving brane in a dilaton gravity background. For the static brane we use the HamiltonJacobi method to study the intrinsic FRW cosmology on the brane and find out the constraint on the bulk potential for the quintessence. We find the similar constraint for the moving brane cases and that the quintessence on it has the effect as a mildly timevarying Newton constant.
COSMIC ACCELERATION: PAST AND PRESENT
, 2011
"... Our Universe has an exciting history of accelerated expansion. Following its inception in an event known as the big bang, the Universe underwent a phase of exponential expansion called inflation. Although precise observations of the cosmic microwave background (CMB) radiation and largescale struc ..."
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Our Universe has an exciting history of accelerated expansion. Following its inception in an event known as the big bang, the Universe underwent a phase of exponential expansion called inflation. Although precise observations of the cosmic microwave background (CMB) radiation and largescale structure support the inflationary paradigm, the absence of a firm physical mechanism for inflation has led to a plethora of theoretical embarkments attempting to understand its genesis. Inflation lasted only for a fraction of a second, but observations suggest that thirteen billion years after inflation, the Universe began accelerating once again. This acceleration, which continues till date, is attributed to a mysterious component, dubbed dark energy, that fills up our Universe and accounts for almost 73 % of the total energy density in the Universe. In this thesis we study and develop models of inflation and dark energy, in the light of current observations. We begin, in Chapter 1, with a detailed introduction to cosmic acceleration, and discuss various models of inflation and dark energy that have been studied in the literature in the recent years. In Chapter 2, we discuss how a hierarchy of
Nonminimal
, 710
"... coupling as a mechanism for spontaneous symmetry breaking on the brane ..."
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Holographic Cosmic Quintessence on
, 2001
"... Recently quintessence is proposed to explain the observation data of supernova indicating a timevarying cosmological constant and accelerating universe. Inspired by this and its mysterious origin, we look for the possibility of quintessence as the holographic dark matters dominated in the late time ..."
Abstract
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Recently quintessence is proposed to explain the observation data of supernova indicating a timevarying cosmological constant and accelerating universe. Inspired by this and its mysterious origin, we look for the possibility of quintessence as the holographic dark matters dominated in the late time in the brane world scenarios. We consider both the cases of static and moving brane in a dilaton gravity background. For the static brane we use the HamiltonJacobi method motivated by holographic renormalization group to study the intrinsic FRW cosmology on the brane and find out the constraint on the bulk potential for the quintessence. This constraint requires a negative slowly varying bulk potential which implies an antide Sitterlike bulk geometry and could be possibly realized from the higher dimensional supergravities or string theory. We find the similar constraint for the moving brane cases and that the quintessence on it has the effect as a mildly timevarying Newton constant.
Dark Energy in Extra Dimensions and String Theory: Consistency Conditions
, 2000
"... The smallness of the cosmological constant is one of the basic problems in particle physics and cosmology. Various attempts have been made to explain this mystery, but no satisfactory solution has been found yet. The appearance of extra dimensions in the framework of brane world systems seems to pro ..."
Abstract
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The smallness of the cosmological constant is one of the basic problems in particle physics and cosmology. Various attempts have been made to explain this mystery, but no satisfactory solution has been found yet. The appearance of extra dimensions in the framework of brane world systems seems to provide some new ideas to address this problem form a different point of view. We shall discuss some of these new approaches and see whether or not they lead to an improvement of the situation. We shall conclude that we are still far from a solution of the problem.