Supergravity, D-brane Probes and thermal super Yang-Mills: a comparison

A D3-brane probe in the context of AdS/CFT correspondence at finite temperature is considered. The supergravity predictions for the physical effective couplings of the world-volume gauge theory of the probe brane are compared to those calculated in one-loop perturbation theory in the thermal gauge theory. It is argued that when the Higgs expectation value is much larger than the temperature, the supergravity result must agree with perturbative thermal Yang-Mills. This provides a perturbative test of the Maldacena conjecture. Predictions for the running electric and magnetic effective couplings, beyond perturbation theory are also obtained. Phenomenological applications for universe-branes are discussed. In particular mechanisms are suggested for reducing the induced cosmological constant and naturally obtaining a varying speed of light and a consequent inflation on the universe brane.Comment: LaTeX, 23 pages, 4 eps figures; v2: Comparison with Tseytlin-Yankielowicz ammended. Extra discussion on reduced supersymmetry on branes added; v3: A few minor changes to improve presentation. Version published in JHEP10(1999)1

Duality Symmetries and Topology Change in String Theory

Duality symmetries for strings moving in non-trivial spacetime backgrounds are analysed. It is shown that for backgrounds generated from WZW and coset CFT models such duality symmetries are exact to all orders in string perturbation theory. Their implications for string dynamics in non-trivial/singular spacetimes are discussed. (Talk given at the EPS 93 Conference, held at Marseille, July 22-27. To appear in the Proceedings.)Comment: lateX file, 6pp. CERN-TH.7003/9

4D gravity on a brane from bulk higher-curvature terms

We study a gravity model where a tensionful codimension-one three-brane is embedded on a bulk with infinite transverse length. We find that 4D gravity is induced on the brane already at the classical level if we include higher-curvature (Gauss-Bonnet) terms in the bulk. Consistency conditions appear to require a negative brane tension as well as a negative coupling for the higher-curvature terms.Comment: 10 pages, no figures; a minor change in wording (to appear in MPLA

Perturbative and Non-Perturbative Partial Supersymmetry Breaking; N=4 -> N=2 -> N=1

We show the existence of a supersymmetry breaking mechanism in string theory, where N=4 supersymmetry is broken spontaneously to N=2 and N=1 with moduli dependent gravitino masses. The spectrum of the spontaneously broken theory with lower supersymmetry is in one-to-one correspondence with the spectrum of the heterotic N=4 string. The mass splitting of the N=4 spectrum depends on the compactification moduli as well as the three R-symmetry charges. We also show that, in string theory, chiral theories can be obtained after spontaneous breaking of extended supersymmetry. This was impossible at the level of field theory. In the large moduli limit a restoration of the N=4 supersymmetry is obtained. As expected the graviphotons and some of the gauge bosons become massive in N=1 vacua. At some special points of the moduli space some of the N=4 states with non-zero winding numbers and with spin 0 and {1/2} become massless chiral superfields of the unbroken N=1 supersymmetry. Such vaccua have a dual type II description, in which there are magnetically charged states with spin 0 and {1/2} that become massless. The heterotic-type II duality suggests some novel non-perturbative transitions on the type II side. Such transitions do not seem to have a geometric interpretation, since they relate type II vaccua with symmetric worlsheet structure to assymetric ones. The heteroric interpretation of such a transition is an ordinary Higgsing of an SU(2) factor. In the case of N=4 --> N=2, the perturbative N=2 prepotential is determined by the perturbative N=4 BPS states. This observation let us to suggest a method which determines the exact non-perturbative prepotential of the effective N=2 supergravity using the shifted spectrum of the non-perturbative BPS states of the underlying N=4 theory.Comment: 36 pages, Latex. An important part is added. We point out that there are string theory groundstates with spontaneously broken extended supersymmetry and chiral spectru

Mirage Cosmology

A brane universe moving in a curved higher dimensional bulk space is considered. The motion induces a cosmological evolution on the universe brane that is indistiguishable from a similar one induced by matter density on the brane. The phenomenological implications of such an idea are discussed. Various mirage energy densities are found, corresponding to dilute matter driving the cosmological expansion, many having superluminal properties $|w|>1$ or violating the positive energy condition. It is shown that energy density due to the world-volume fields is nicely incorporated into the picture. It is also pointed out that the initial singularity problem is naturally resolved in this context.Comment: JHEP LateX, 20 pages, no figures;v2 references added and a few minor changes; (v3) Corrected an inconsequential error in eq. 6.2, 6.3. We thank D. Kutasov for bringing this to our attention (v4) Corrected inconsequential errors in (4.4)-(4.7) and (5.11). We thank A. Psinas for bringing them to our attentio

U-duality and D-brane Combinatorics

We investigate D-brane instanton contributions to R^4 couplings in any toroidal compactification of type II theories. Starting from the 11D supergravity one-loop four-graviton amplitude computed by Green, Gutperle and Vanhove, we derive the non-perturbative O(e^{-1/\lambda}) corrections to R^4 couplings by a sequence of T-dualities, and interpret them as precise configurations of bound states of D-branes wrapping cycles of the compactification torus. Dp-branes explicitely appear as fluxes on D(p+2)-branes, and as gauge instantons on D(p+4)-branes. Specific rules for weighting these contributions are obtained, which should carry over to more general situations. Furthermore, it is shown that U-duality in D<=6 relates these D-brane configurations to O(e^{-1/\lambda^2}) instantons for which a geometric interpretation is still lacking.Comment: 17 pages, LaTeX2e, intro. shortened and minor typos corrected, final versio

Thermodynamics of D-brane Probes

We discuss the dynamics and thermodynamics of particle and D-brane probes moving in non-extremal black hole/brane backgrounds. When a probe falls from asymptotic infinity to the horizon, it transforms its potential energy into heat, $TdS$, which is absorbed by the black hole in a way consistent with the first law of thermodynamics. We show that the same remains true in the near-horizon limit, for BPS probes only, with the BPS probe moving from AdS infinity to the horizon. This is a quantitative indication that the brane-probe reaching the horizon corresponds to thermalization in gauge theory. It is shown that this relation provides a way to reliably compute the entropy away from the extremal limit (towards the Schwarzschild limit).Comment: 12 pages; Based on talks presented at the midterm meeting of the TMR network "Physics beyond the standard model," held in Trieste in March 1999, and at the 1998 Corfu Summer Institute on Elementary Particle Physic

Heterotic/Type-I Duality in D<10 Dimensions, Threshold Corrections and D-Instantons

We continue our study of heterotic/type-I duality in D<10 dimensions. We consider the heterotic and type-I theories compactified on tori to lower dimensions. We calculate the special (``BPS saturated'') F^4 and R^4 terms in the effective one-loop heterotic action. These terms are expected to be non-perturbatively exact for D>4. The heterotic result is compared with the associated type-I result. In D<9 dimensions, the type-I theory has instanton corrections due to D1 instantons. In D=8 we use heterotic-type I duality to give a simple prescription of the D-instanton calculation on the type I side. We allow arbitrary Wilson lines and show that the D1-instanton determinant is the affine character-valued elliptic genus evaluated at the induced complex structure of the D1-brane world-volume. The instanton result has an expansion in terms of Hecke operators that suggest an interpretation in terms of an SO(N) matrix model of the D1-brane. The total result can be written in terms of generalized prepotentials revealing an underlying holomorphic structure. In D<8 we calculate again the heterotic perturbative thresholds and show that they agree with the D1-instanton calculation using the rules derived in D=8.Comment: Latex, 67 pages, 1 figur

A Large Class of New Gravitational and Axionic Backgrounds for Four-Dimensional Superstrings

A large class of new 4-D superstring vacua with non-trivial/singular geometries, spacetime supersymmetry and other background fields (axion, dilaton) are found. Killing symmetries are generic and are associated with non-trivial dilaton and antisymmetric tensor fields. Duality symmetries preserving N=2 superconformal invariance are employed to generate a large class of explicit metrics for non-compact 4-D Calabi-Yau manifolds with Killing symmetries.Comment: LateX file, 34pp., (v5) Some misprints corrected in sections 3.1, 3.2 as pointed out in the paper of Hori and Kapustin (hep-th/0203147). Some comsetic changes also made in the same section