The stringy nature of the 2d type-0A black hole

We investigate the thermodynamics of the RR charged two-dimensional type-0A black hole background at finite temperature, and compare with known 0A matrix model results. It has been claimed that there is a disagreement for the free energy between the spacetime and the dual matrix model. Here we find that this discrepancy is sensitive to how the cutoff is implemented on the spacetime side. In particular, the disagreement is resolved once we put the cutoff at a fixed distance away from the horizon, as opposed to a fixed position in space. Furthermore, the mass and the entropy of the black hole itself add up to an analytic contribution to the free energy, which is precisely reproduced by the 0A matrix model. We also use results from the 0A matrix model to predict the next to leading order contribution to the entropy of the black hole. Finally, we note that the black hole is characterized by a Hagedorn growth in its density of states below the Hagedorn temperature. This, together with other results, suggests there is a phase transition at this temperature.Comment: 1+21 pages; v2: Substantial changes in the body of the paper, main results the same. Clarified discussion on the thermodynamics, added section on a phase transition, references added. v3: Typos corrected. v4: Final version, to appear in JHE

On the string interpretation of M(atrix) theory

It has been proposed recently that, in the framework of M(atrix) theory, N=8 supersymmetric U(N) Yang-Mills theory in 1+1 dimensions gives rise to type IIA long string configurations. We point out that the quantum moduli space of $SYM_{1+1}$ gives rise to two quantum numbers, which fit very well into the M(atrix) theory. The two quantum numbers become familiar if one switches to a IIB picture, where they represent configurations of D-strings and fundamental strings. We argue that, due to the SL(2,Z) symmetry, of the IIB theory, such quantum numbers must represent configurations that are present also in the IIA framework.Comment: 13 pages, Latex, more comment

Ramond-Ramond (boundary) states

The description of D-branes as boundary states for type II string theories (in the covariant formulation) requires particular care in the R-R sector. Also the vertices for R-R potentials that can couple to D-branes need a careful handling. As an illustration of this, the example of the D0-D8 system is reviewed, where a ``microscopic'' description of the interaction via exchange of R-R potentials becomes possible.Comment: 8 pages, LaTeX, no figures. Talk presented at the 2nd Conference on Quantum aspects of Gauge Theories, Supersymmetry and Unification, Corfu, Greece, 21-26 September 199

String Junction Transitions in the Moduli Space of N=2 SYM

The string theory description of BPS states in D-brane world-volume field theories may undergo transitions from open strings to string webs, as well as between different string webs, as one moves in the field theory moduli space. These transitions are driven by the string creation phenomenon. We demonstrate such transitions in the D3-brane realization of N=2 SU(2) Super-Yang-Mills theory.Comment: 15 pages LaTex, 10 eps figure

P-P' Strings in M(atrix) Theory

We study the off-diagonal blocks in the M(atrix) model that are supposed to correspond to open strings stretched between a Dp-brane and a Dp'-brane. It is shown that the spectrum, including the quantum numbers, of the zero modes in the off-diagonal blocks can be determined from the index theorem and unbroken supersymmetry, and indeed reproduces string theory predictions for p-p' strings. Previously the matrix description of a longitudinal fivebrane needed to introduce extra degrees of freedom corresponding to 0-4 strings by hand. We show that they are naturally associated with the off-diagonal zero modes, and the supersymmetry transformation laws and low energy effective action postulated for them are now derivable from the M(atrix) theory.Comment: minor modification, references added. 21 pages, Latex, minor modification mad

Matrix Compactification On Orientifolds

Generalizing previous results for orbifolds, in this paper we describe the compactification of Matrix model on an orientifold which is a quotient space as a Yang-Mills theory living on a quantum space. The information of the compactification is encoded in the action of the discrete symmetry group G on Euclidean space and a projective representation U of G. The choice of Hilbert space on which the algebra of U is realized as an operator algebra corresponds to the choice of a physical background for the compactification. All these data are summarized in the spectral triple of the quantum space.Comment: 28 pages, late

Quiver Mechanics for Deconstructed Matrix String

In this paper we propose a quiver model of matrix quantum mechanics with 8 supercharges which, on a Higgs branch, deconstructs the worldsheet of Matrix String Theory. This discrete model evades the fermion doubling problem and, in the continuum limit, enhances the number of supersymmetries to sixteen. Our model is motivated by orbifolding the Matrix Model, and the deconstruction {\it ansatz} exhibits a duality between target space compactification and worldsheet deconstruction.Comment: LaTex2e, 16 pages, no figure; v2: More details on fermions added in Appendix. References added; v3: more references added, submitted version; v4: reference adde

Power Spectra in Spacetime Noncommutative Inflation

String/M theory inspires an uncertainty relation between space and time which deviates from general relativity. It is possible to explore this deviation from cosmological observations, in particular from the CMB fluctuation spectrum. This paper extends some previous observations to more general inflation schemes, we find that the noncommutative spacetime effects always suppress the power spectrum, of both the scalar and tensor perturbations, and may provide a large enough running of the spectral index to fit the WMAP data in the inflation model.Comment: 19 pages, 6 figures, harvmac; 2 references added; only references added; Accepted for publication in Nucl. Phys.

Proposal for the Open String Tachyon Effective Action in the Linear Dilaton Background

In this paper we propose tachyon effective actions for unstable D-branes in superstring and bosonic string theories in the presence of the linear dilaton background.Comment: 18 page

Effects of quantum gravity on the inflationary parameters and thermodynamics of the early universe

The effects of generalized uncertainty principle (GUP) on the inflationary dynamics and the thermodynamics of the early universe are studied. Using the GUP approach, the tensorial and scalar density fluctuations in the inflation era are evaluated and compared with the standard case. We find a good agreement with the Wilkinson Microwave Anisotropy Probe data. Assuming that a quantum gas of scalar particles is confined within a thin layer near the apparent horizon of the Friedmann-Lemaitre-Robertson-Walker universe which satisfies the boundary condition, the number and entropy densities and the free energy arising form the quantum states are calculated using the GUP approach. A qualitative estimation for effects of the quantum gravity on all these thermodynamic quantities is introduced.Comment: 15 graghes, 7 figures with 17 eps graph