arXiv subjects
Publications and source records attributed to Shahrokh Parvizi.
In this note, we propose the free energy of general \emph{non-supersymmetric} black hole attractors arising in type IIA(B) superstrings on 3-fold Calabi-Yau, in the supergravity limit. This, by definition, differs from its counterpart BPS free energy by a factor of $4 $. Correspondingly, a mixed ensemble for these black holes is proposed.
In the interesting conjecture, Z_{BH} = |Z_{top}|^2, proposed by Ooguri, Strominger and Vafa (OSV), the black hole ensemble is a mixed ensemble and the resulting degeneracy of states, as obtained from the ensemble inverse-Laplace integration, suffers from prefactors which do not respect the electric-magnetic duality. One idea to overcome this deficiency, as claimed recently, is imposing nontrivial measures for the ensemble sum. We address this problem and upon a redefinition of the OSV ensemble whose variables are as numerous as the electric potentials, show that for restoring the symmetry no non-Euclidean measure is needful. In detail, we rewrite the OSV free energy as a function of new variables which are combinations of the electric-potentials and the black hole charges. Subsequently the Legendre transformation which bridges between the entropy and the black hole free energy in terms of these variables, points to a generalized ensemble. In this context, we will consider all the cases of relevance: small and large black holes, with or without D_6-brane charge. For the case of vanishing D_6-brane charge, the new ensemble is pure canonical and the electric-magnetic duality is restored exactly, leading to proper results for the black hole degeneracy of states. For more general cases, the construction still works well as far as the violation of the duality by the corresponding OSV result is restricted to a prefactor. In a concrete example we shall show that for black holes with non-vanishing D_6-brane charge, there are cases where the duality violation goes beyond this restriction, thus imposing non-trivial measures is incapable of restoring the duality. This observation signals for a deeper modification in the OSV proposal.
We study D-branes in the background of Euclidean AdS2xS2 with a graviphoton field turned on. As the background is not Ricci flat, the graviphoton field must have both self-dual and antiself-dual parts. This, in general, will break all the supersymmetries on the brane. However, we show that there exists a limit for which one can restore half of the supersymmetries. Further, we show that in this limit, the N=1/2 SYM Lagrangian on flat space can be lifted on to the Euclidean AdS2xS2 preserving the same amount of supersymmetries as in the flat case. We observe that without the C-dependent terms present in the action this lift is not possible.
We study {\cal N}=2 SO(2N+1) SYM theory in the context of matrix model. By adding a superpotential of the scalar multiplet, W(Φ), of degree 2N+2, we reduce the theory to {\cal N}=1. The 2N+1 distinct critical points of W(Φ) allow us to choose a vacuum in such a way to break the gauge group to its maximal abelian subgroup. We compute the free energy of the corresponding matrix model in the planar limit and up to two vertices. This result is then used to work out the effective superpotential of {\cal N}=1 theory up to one-instanton correction. At the final step, by scaling the superpotential to zero, the effective U(1) couplings and the prepotential of the {\cal N}=2 theory are calculated which agree with the previous results.
We study supergravity solutions of Dp-branes in the time-dependent orbifold background. We show that worldvolume theories decouple from the bulk gravity for p less than six. Along AdS/CFT correspondence, these solutions could provide the gravity description of noncommutative field theory with time-dependent noncommutative parameter. Type II NS5-brane (M5-brane) in the presence of RR n-form for n=0,..., 4 (C field) in this time-dependent background have also been studied.
We study type IIA superstring theory on a PP-wave background with 24 supercharges. This model can exactly be solved and then quantized. The open string in this PP-wave background is also studied. We observe that the theory has supersymmetric Dp-branes for p=2,4,6,8.
Dirichlet p-branes in the background of pp waves are constructed using the massive Green-Schwarz worldsheet action for open strings. These branes are localized at the origin and only for $p=7, 5, 3$ preserve half the supersymmetries. The spectrum of the brane theory is analyzed and is found to be in agreement with the spectrum of the small fluctuations of the world-volume super Yang-Mills theory in this background. These branes are expected to correspond to objects that are nonperturbative in $N$ in the dual gauge theory.
By using the so-called Information Metric on the moduli space of an anti-selfdual (ASD) Instanton in a Self-Dual (SD) Non-Commutative background, we investigate the geometry of moduli space. The metric is evaluated perturbatively in non-commutativity parameter and we show that by putting a cut-off in the location of instanton in the definition of Information Metric we can recover the five dimensional space time in the presence of a B-field. This result shows that the non-commutative YM-Instanton Moduli corresponds to D-Instanton Moduli in the gravity side where the radial and transverse location of D-Instanton are corresponding to YM-Instanton size and location, respectively. The match is shown in the first order of non-commutativity parameter.
Dynamics of D-branes on $SU(2)/U(1)$ gauged WZW model are investigated. We find the effective action for infinite $k$, where $k$ is the level of WZW model. We also consider finite $k$ correction to the effective action which is compatible with Fedosov's deformation quantization of the background.
We investigate the Kac-Moody algebra of noncommutative Wess-Zumino-Witten model and find its structure to be the same as the commutative case. Various kinds of gauged noncommutative WZW models are constructed. In particular, noncommutative $U(2)/U(1)$ WZW model is studied and by integrating out the gauge fields, we obtain a noncommutative non-linear $σ$-model.
By adding gauge fields to the D-string classical solution, which have non-zero contribution to commutators in continuum limit (extreme large $N$), we introduced $(m,n)$-strings in IIB matrix model. It is found that the size of matrices depends on the value of the electric field. The tension of these strings appears in $SL(2,Z)$ invariant form. The interaction for parallel and angled strings are found in agreement with the string theory for small electric fields.
It is argued that quantum traveling of D-particles presents the ``joining-splitting'' processes of field theory Feynman graphs. The amplitudes in $d$ dimensions can be corresponded with those of a $d+2$ dimensional theory in the Light-Cone frame. It is shown that this Light-Cone formulation enables to study processes with arbitrary longitudinal momentum transfers. It is discussed that a massless sector exists which can be taken as the low energy limit. By taking the constant relative distance in the bound-states we find a spectrum for the intermediatory fields.
Different BPS M-brane configurations including single and two parallel M$p$-branes ($p$= even) and M5-branes are introduced as the classical solutions of the recently proposed Static Matrix Model. Also the long range interactions of two relatively rotated M$p$-branes (one and two angles) and M$p$-brane--anti-M$p$-brane are calculated. The results are in agreement with 11 dimensional supergravity results.