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We extend the model of a 5D Brans–Dicke gravity theory reduced to 4D through the presence of a hypersurface-orthogonal space-like killing vector field in the underlying 5D spacetime by including a varying speed of light. The resulting model is characterized by the presence of two scalar fields. We focus on late-time power law solutions which emerge in general when scalar fields couple to spacetime curvature and do not contradict the SNIa astrophysical data. Analytic solutions in 4-dimensions are derived and late-time accelerated expansion was found. The universe is dominated by dark energy, free from phantom field and is characterized by a decaying energy matter density, decaying scalar fields, and a decreasing celerity of light. The model is confronted with astrophysical observations and is found to fit these data.

Recently, the quantum spectrum of black holes has been considered. We will show that this spectrum depends on the shape of manifolds that form black holes. For example, black holes with heptagonal shapes have more energy and less temperature with respect to the ones with pentagonal or hexagonal shapes.

Recently, some authors showed that a classical collapse scenario ignores this richness of information in the resulting spectrum and a consistent quantum treatment of the entire collapse process might allow us to retrieve much more information from the spectrum of the final radiation. We confirm these results and show that by considering the quantum entanglement between metrics, we can uncover information of black holes. In our model, a density matrix is defined for the spaces, both inside and outside of the event horizon. These inside and outside spaces of black holes are obtained by tracing from a bigger space. An observer that lives in this big space can recover total information regarding the inside and outside of black hole.

A Brans–Dicke brane cosmology with two scalar fields inspired from string theories and phenomenological effective cosmological constant is investigated and some features are described in some details, in particular the low and high energies limit.

We investigate the relation between large N duality applied to systems of D5's and [Formula: see text]'s wrapping vanishing cycles of local CY in type IIB and M-theory lifts of the NS5/D4/[Formula: see text] systems in type IIA to which they are related by T-duality. Through a simple example based on a local CY constructed using an A2 singularity, we review this well-known correspondence in the supersymmetric setting and describe the manner in which it generalizes when antibranes are added. Agreement between the IIB and IIA pictures, which supports the assertion that [Formula: see text] supersymmetry is spontaneously broken in these systems at string tree level, is demonstrated when gs ≪ 1. Novel nonholomorphic features can arise away from this regime and their physical origin is discussed. This note is based on talks given at KITP, Harvard University, TIFR, the University of Tokyo at Hongo, the 2007 Les Houches Summer School, and the 2007 Simons Workshop, is based on work done in collaboration with K. Papadodimas and M. Shigemori, and contains some previously unpublished results.

In ten dimensions, SO(8) triality encourages confusion between fermions ans bosons, but in eleven dimensions, SO(9) has no such features. Yet this is the domain of M — theory whose infrared limit is the divergent supergravity field theory. Curtright ascribes this divergence to an incomplete cancellation among the Dynkin indices between the supergravity representations. We speculate that an infinite number of the recently discovered Euler triplets, describing massless particles of higher spin, can cancel the divergences of eleven dimensional supergravity, perhaps providing a clue to M — theory.

The SO(2,10) covariant extension of M-theory superalgebra is considered, with the aim to construct a correspondingly generalized M-theory, or 11d supergravity. For the orbit, corresponding to the $11d$ supergravity multiplet, the simplest unitary representations of the bosonic part of this algebra, with sixth-rank tensor excluded, are constructed on a language of field theory in 66d space-time. The main peculiarities are the presence of more than one equation of motion and corresponding Lagrangians for a given field and that the gauge and SUSY invariances of the theory mean that the sum of variations of these Lagrangians (with different variations of the same field) is equal to zero., Latex 16 pages, minor correction, To appear in Mod. Phys. Lett. A

By working with the free energy for the type II supergravity near-horizon solution of N coincident non-extremal Dp-branes we study the transitions among the non-conformal Dp-brane system, the perturbative super Yang-Mills theory and a certain system associated with M theory. We derive a relation between this free energy and the action of a Dp-brane probe in the N Dp-brane background. Constructing the free energy for the five dimensional black hole labeled by the D1-brane and D5-brane charges we find the similar relation between it and the action of a D1 or D5 brane probe in the D1 + D5 brane background. These relations are explained by the massive open strings stretched between the relevant D-branes, Comment: 14 pages, LaTeX2e, no figures

We generalize the M-theoretic duality of Schmaltz and Sundrum to the product group SU(N) x SU(N') case. We show that the type IIA brane configurations for dual gauge theories are in fact two special limits of the same M-theory 5-brane, just as in the case of the simple SU(N) group., Latex, 15 pages, 4 figures. The title, abstract and contents are modified in order to give a more clear presentation. The misleading remark on S-duality transformation is removed. The version to appear in Mod. Phys. Lett. A

The infinite limit of Matrix Theory in 4 and 10 dimensions is described in terms of Moyal Brackets. In those dimensions there exists a Bogomol'nyi bound to the Euclideanized version of these equations, which guarantees that solutions of the first order equations also solve the second order Matrix Theory equations. A general construction of such solutions in terms of a representation of the target space co-ordinates as non-local spinor bilinears, which are generalisations of the standard Wigner functions on phase space, is given., Comment: 10 pages, Latex, no figures. References altered, typos corrected

We propose a supergravity model that contains elements recently shown to arise in the strongly-coupled limit of the $E_8\times E_8$ heterotic string (M-theory), including a no-scale--like K\"ahler potential, the identification of the string scale with the gauge coupling unification scale, and the onset of supersymmetry breaking at an intermediate scale determined by the size of the eleventh dimension of M-theory. We also study the phenomenological consequences of such scenario, which include a rather constrained sparticle spectrum within the reach of present-generation particle accelerators., Comment: 8 pages, LaTeX, 3 figures (included)

We discuss some properties of a supersymmetric matrix model that is the dimensional reduction of supersymmetric Yang-Mills theory in ten dimensions and which has been recently argued to represent the short-distance structure of M theory in the infinite momentum frame. We describe a reduced version of the matrix quantum mechanics and derive the Nicolai map of the simplified supersymmetric matrix model. We use this to argue that there are no phase transitions in the large-N limit, and hence that S-duality is preserved in the full eleven dimensional theory., 11 pages LaTeX; Clarifying comments and additional references added

Taking the (2,2) strings as a starting point, we discuss the equivalent integrable field theories and analyze their symmetry structure in 2+2 dimensions from the viewpoint of string/membrane unification. Requiring the Lorentz invariance and supersymmetry in the (2,2) string target space leads to an extension of the (2,2) string theory to a theory of 2+2 dimensional supermembranes (M-branes) propagating in a higher dimensional target space. The origin of the hidden target space dimensions of the M-brane is related to the maximally extended supersymmetry implied by the Lorentz covariance and dimensional reasons. The K"ahler-Chern-Simons-type action describing the self-dual gravity in 2+2 dimensions is proposed. Its maximal supersymmetric extension (of the Green-Schwarz-type) naturally leads to the 2+10 (or higher) dimensions for the M-brane target space. The proposed OSp(32|1) supersymmetric action gives the pre-geometrical description of M-branes, which may be useful for a fundamental formulation of F&M theory., 12 pages, LaTeX, misprints corrected, the final version to appear in the Modern Physics Letters A