119062307
Comments on the renormalizability of the Broken Phase in Noncommutative Scalar Field Theory
We study the noncommutative 4 theory with spontaneously broken global O(2) symmetry in 4 dimensions. We demonstrate the renormalizability at one loop. This does not require any choice of ordering of the fields in the interaction terms. It involves regulating the ultraviolet and infrared divergences in a manner consistent with the Ward identities.
119237728
Strong Coupling BCS Superconductivity and Holography
Abstract We attempt to give a holographic description of the microscopic theory of a BCS superconductor. Exploiting the analogy with chiral symmetry breaking in QCD we use the Sakai–Sugimoto model of two D8 branes in a D4 brane background with finite baryon number. In this case there is a new tachyonic instability which is plausibly the bulk analog of the Cooper pairing instability. We analyze the Yang–Mills approximation to the non-Abelian Dirac–Born–Infeld action. We give some exact solutions of the non-linear Yang–Mills equations in flat space and also give a stability analysis, showing that the instability disappears in the presence of an electric field. The holographic picture also suggests a dependence of T c on the number density which is different from the usual (weak coupling) BCS. The flat space solutions are then generalized to curved space numerically and also, in an approximate way, analytically. This configuration should then correspond to the ground state of the boundary superconducting (superfluid) ground state. We also give some preliminary results on Green functions computations in the Sakai–Sugimoto model without any chemical potential.
624279
Phase Transitions in Higher Derivative Gravity
This paper deals with black holes, bubbles and orbifolds in Gauss–Bonnet theory in five dimensional anti de Sitter space. In particular, we study stable, unstable and metastable phases of black holes from thermodynamical perspective. By comparing bubble and orbifold geometries, we analyse associated instabilities. Assuming AdS/CFT correspondence, we discuss the effects of this higher derivative bulk coupling on a specific matrix model near the critical points of the boundary gauge theory at finite temperature. Finally, we propose another phenomenological model on the boundary which mimics various phases of the bulk space-time.
119340528
Aspects of open-closed duality in a background B-field
We study closed string exchanges in background B-field. By analysing the two point one loop amplitude in bosonic string theory, we show that tree-level exchange of lowest lying, tachyonic and massless closed string modes, have IR singularities similar to those of the nonplanar sector in noncommutative gauge theories. We further isolate the contributions from each of the massless modes. We interpret these results as the manifestation of open/closed string duality, where the IR behaviour of the boundary noncommutative gauge theory is reconstructed from the bulk theory of closed strings.
18164758
Closed string exchanges on C2/Z2 in a background B-field
In an earlier work it was shown that the IR singularities arising in the nonplanar one loop two point function of a noncommutative = 2 gauge theory can be reproduced exactly from the massless closed string exchanges. The noncommutative gauge theory is realised on a fractional D3 brane localised at the fixed point of the C2/Z2 orbifold. In this paper we identify the contributions from each of the closed string modes. The sum of these adds up to the nonplanar two-point function.
15306576
On the UV renormalizability of noncommutative field theories
UV/IR mixing is one of the most important features of noncommutative field theories. As a consequence of this coupling of the UV and IR sectors, the configuration of fields at the zero momentum limit in these theories is a very singular configuration. We show that the renormalization conditions set at a particular momentum configuration with a fixed number of zero momenta, renormalizes the Green's functions for any general momenta only when this configuration has same set of zero momenta. Therefore only when renormalization conditions are set at a point where all the external momenta are nonzero, the quantum theory is renormalizable for all values of nonzero momentum. This arises as a result of different scaling behaviors of Green's functions with respect to the UV cutoff (Λ) for configurations containing different set of zero momenta. We study this in the noncommutative 4 theory and analyse similar results for the Gross-Neveu model at one loop level. We next show this general feature using Wilsonian RG of Polchinski in the globally O(N) symmetric scalar theory and prove the renormalizability of the theory to all orders with an infrared cutoff. In the context of spontaneous symmetry breaking (SSB) in noncommutative scalar theory, it is essential to note the different scaling behaviors of Green's functions with respect to Λ for different set of zero momenta configurations. We show that in the broken phase of the theory the Ward identities are satisfied to all orders only when one keeps an infrared regulator by shifting to a nonconstant vacuum.
122930946
Holographic dark energy model with linearly varying deceleration parameter and generalised Chaplygin gas dark energy model in Bianchi type-I universe
The paper deals with a spatially homogeneous and anisotropic Bianchi type-I universe filled with two minimally interacting fluids; matter and holographic dark energy components. The nature of the holographic dark energy for Bianchi type-I space time is discussed. An exact solution to Einstein’s field equations in Bianchi type-I line element is obtained using the assumption of linearly varying deceleration parameter. Under the suitable condition, it is observed that the anisotropy parameter of the universe approaches to zero for large cosmic time and the coincidence parameter increases with increasing time. We established a correspondence between the holographic dark energy models with the generalised Chaplygin gas dark energy model. We also reconstructed the potential and dynamics of the scalar field which describes the Chaplygin cosmology. Solution of the field equations shows that a big rip type future singularity will occur for this model. It has been observed that the solutions are compatible with the results of recent observations.
119290419
Hawking radiation as tunneling for spherically symmetric black holes: A generalized treatment
Abstract We present a derivation of Hawking radiation through tunneling mechanism for a general class of asymptotically flat, spherically symmetric spacetimes. The tunneling rate Γ ∼ exp ( Δ S ) arises as a consequence of the first law of thermodynamics, T d S = d E + P d V . Therefore, this approach demonstrates how tunneling is intimately connected with the first law of thermodynamics through the principle of conservation of energy. The analysis is also generally applicable to any reasonable theory of gravity so long as the first law of thermodynamics for horizons holds in the form, T d S = d E + P d V .
119281634
Second Law Violations in Lovelock Gravity for Black Hole Mergers
We study the classical second law of black hole thermodynamics, for Lovelock theories (other than general relativity), in arbitrary dimensions. Using the standard formula for black hole entropy, we construct scenarios involving the merger of two black holes in which the entropy instantaneously decreases. Our construction involves a Kaluza-Klein compactification down to a dimension in which one of the Lovelock terms is topological. We discuss some open issues in the definition of the second law which might be used to remove this entropy decrease.
121595572
Dimensional regularisation and broken conformal Ward identities
Abstract Dimensional regularization is used to give a simple treatment of broken conformal Ward identities. The method reproduces the known answers for standard theories. In addition it permits a derivation of the relevant identities for non-Abelian gauge theories which have not been obtained by other means. For the latter class of theories asymptotic scale invariance is found not to imply asymptotic conformal invariance for gauge variant Green functions. This is due to two gauge dependent insertions occurring in the identities. One can be predicted classically, whereas the other contains a new term dependent on Faddeev-Popov ghosts.
61175398
VAX Q-bus to CAMAC systems crate interface for long CAMAC branches
The TRIUMF Central Control System (CCS) was to be upgraded to use Q-bus-based VAXs. The CCS consists of multiple computers interfaced to a CAMAC Executive Crate with long parallel branches containing multiple pairs of differential branch extenders (DBE). The Creative Electronics System SCI 2280 systems crate interface used for the Q-bus VAX requires the CAMAC operation to complete synchronously with the Q-bus cycle in less than the Q-bus timeout period. This translates to a maximum branch length of about 150 meters containing three pairs of DBEs, which was not adequate. A Q-bus-to-SCI 2280 interface was built to allow CAMAC cycles to be decoupled, when desired, from the Q-bus cycles. When cycles are decoupled, completion of the CAMAC part can be ascertained by testing flags in the interface. The interface design and operation are described and the results of tests using a VAX 3500 are given.<<ETX>>