Some Interesting Properties of Field theories with an Infinite Number of Fields

We give an indication that gravity coupled to an infinite number of fields might be a renormalizable theory. A toy model with an infinite number of interacting fermions in four-dimentional space-time is analyzed. The model is finite at any order in perturbation theory. However, perturbation theory is valid only for external momenta smaller than $\lambda ^{-\frac{1}{2}}$ , where $\lambda$ is the coupling constant.Comment: 12 pages, LaTe

Information Loss in Quantum Gravity Without Black Holes

We use the weak field approximation to show that information is lost in principle in quantum gravity.Comment: 14pp, Late

On the M-Theory Approach to (Compactified) 5D Field Theories

We construct M-theory curves associated with brane configurations of SU(N), SO(N) and $Sp(2N)$ 5d supersymmetric gauge theories compactified on a circle. From the curves we can account for all the existing different SU(N) field theories with $N_f \leq 2 N$. This is the correct bound for $N \geq 3$. We remark on the exceptional case SU(2). The bounds obtained for SO(N) and $Sp(2N)$ are $N_f\leq N-4$ and $N_f\leq 2N+4$, respectively.Comment: 18 pages, minor correction

Wilson Loops in the Large N Limit at Finite Temperature

Using a proposal of Maldacena we compute in the framework of the supergravity description of N coincident D3 branes the energy of a quark anti-quark pair in the large N limit of U(N) N=4 SYM in four dimensions at finite temperature.Comment: 7 pages, LaTeX2e, 5 eps figures; references added and corrected, typos correcte

Black Hole Horizon Fluctuations

It is generally admitted that gravitational interactions become large at an invariant distance of order $1$ from the black hole horizon. We show that due to the ``atmosphere'' of high angular particles near the horizon strong gravitational interactions already occur at an invariant distance of the order of $\sqrt[3]{M}$. The implications of these results for the origin of black hole radiation, the meaning of black hole entropy and the information puzzle are discussed.Comment: Latex, 22 pages (minor corrections and precisions added

Free Energies and Probe Actions for Near-horizon D-branes and D1 + D5 System

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-branesComment: 14 pages, LaTeX2e, no figure

Stringy effect of the holographic correspondence for Dp-brane backgrounds

Based on the holographic conjecture for superstrings on Dp-brane backgrounds and the dual (p+1)-dimensional gauge theory ($0\le p\le 4$) given in hep-th/0308024 and hep-th/0405203, we continue the study of superstring amplitudes including string higher modes ($n\ne 0$). We give a prediction to the two-point functions of operators with large R-charge J. The effect of stringy modes do not appear as the form of anomalous dimensions except for p=3. Instead, it gives non-trivial correction to the two-point functions for supergravity modes. For p=4, the scalar two-point functions for any n behave like free fields of the effective dimension d_{eff}=6 in the infra-red limit.Comment: 23 pages, typos correcte

Inflection Point Inflation and Time Dependent Potentials in String Theory

We consider models of inflection point inflation. The main drawback of such models is that they suffer from the overshoot problem. Namely the initial condition should be fine tuned to be near the inflection point for the universe to inflate. We show that stringy realizations of inflection point inflation are common and offer a natural resolution to the overshoot problem.Comment: 15 pages, 2 figures, refs. adde