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R. Parthasarathy

Publications and source records attributed to R. Parthasarathy.

At least 37 records · Page 2Linked to original sources

Optical Activity From Extra Dimension

Optical activity, like Faraday effect, is a rotation of the plane of polarization of propagating light in a medium and can be attributed to different sources with distinct signatures. In this note we discuss the effect of optical activity {\it{in vacuum}} due to Kaluza-Klein scalar field $ϕ$, in the presence of an external electro-magnetic field. The astrophysical implication of this effect is indicated. We also point out the possibility of observing the same in laboratory conditions.

astro-ph↗

Coherent Spin Oscillations in a Disordered Magnet

Most materials freeze when cooled to sufficiently low temperature. We find that magnetic dipoles randomly distributed in a solid matrix condense into a spin liquid with spectral properties on cooling that are the diametric opposite of those for conventional glasses. Measurements of the non-linear magnetic dynamics in the low temperature liquid reveal the presence of coherent spin oscillations composed of hundreds of spins with lifetimes up to ten seconds. These excitations can be labeled by frequency, manipulated by the magnetic fields from a loop of wire, and permit the encoding of information at multiple frequencies simultaneously.

cond-mat↗

NS5 Brane and Little String Duality in the pp-wave Limit

We study NSR strings in the Nappi-Witten background, which is the Penrose limit of a certain NS5-brane supergravity solution. We solve the theory in the light-cone gauge, obtaining the spectrum, which is space-time supersymmetric. In light of the LST/NS5-brane duality, this spectrum should be in correspondence with the states of little string theory in the appropriate limit. A semiclassical analysis verifies that the relationship between energy and angular momentum, after a field redefinition, matches the known result for a flat background.

hep-th↗

Non-Linear Sigma Model on Conifolds

Explicit solutions to the conifold equations with complex dimension $n=3,4$ in terms of {\it{complex coordinates (fields)}} are employed to construct the Ricci-flat Kähler metrics on these manifolds. The Kähler 2-forms are found to be closed. The complex realization of these conifold metrics are used in the construction of 2-dimensional non-linear sigma model with the conifolds as target spaces. The action for the sigma model is shown to be bounded from below. By a suitable choice of the 'integration constants', arising in the solution of Ricci flatness requirement, the metric and the equations of motion are found to be {\it{non-singular}}. As the target space is Ricci flat, the perturbative 1-loop counter terms being absent, the model becomes topological. The inherent U(1) fibre over the base of the conifolds is shown to correspond to a gauge connection in the sigma model. The same procedure is employed to construct the metric for the resolved conifold, in terms of complex coordinates and the action for a non-linear sigma model with resolved conifold as target space, is found to have a minimum value, which is topological. The metric is expressed in terms of the six real coordinates and compared with earlier works. The harmonic function, which is the warp factor in Type II-B string theory, is obtained and the ten-dimensional warped metric has the $AdS_{5}\times X_{5}$ geometry.

hep-th↗

Confining Configurations in QCD and Relation to Rigid Strings

The gauge field configurations of QCD gauge fields in the infrared regime are obtained by magnetic symmetry condition. The effective dual action exhibits dual Meissner effect with quarks included. A string representation of this action corresponds to rigid string.

hep-lat↗

Geometric Properties of QCD String From Willmore Functional

The extremum of the Willmore-like functional for $m$-dimensional Riemannian surface immersed in $d$-dimensional Riemannian manifold under normal variations is studied and various cases of interest are examined. This study is used to relate the parameters of QCD string action, including the Polyakov-Kleinert extrinsic curvature action, with the geometric properties of the world sheet. The world sheet has been shown to have {\it{negative stiffness}} on the basis of geometric considerations.

hep-th↗

Supersymmetry in Thermo Field Dynamics

By considering the enlarged thermal system including the heat bath, it is shown that this system has supersymmetry which is not broken at finite temperature. The super algebra is constructed and the Hamiltonian is expressed as the anti-commutator of two kinds of super charges. With this Hamiltonian and the thermal vacuum $\mid 0(β)>$, this supersymmetry is found to be preserved.

cond-mat↗

Spontaneous Time Asymmetry due to Horizon

We show that quantized matter fields in the presence of background metrics with Horizon exhibit spontaneous time asymmetry. All quantized matter fields have to vanish at the horizon. Some phenemenological applications of this in the context of black holes and early universe are considered.

hep-th↗

Infrared region of QCD and confining strings

Gauge field configurations appropriate for the infrared region of QCD are proposed in a submanifold of $su(3)$. Some properties of the submanifold are presented. Using the usual action for QCD, in the absense of quarks, confinement of these configurations is realized as in the London theory of Meissner effect. Choosing a representation for the monopole field strength, a string action corresponding to the effective gauge theory action in the infrared region, is obtained. This confining string action contains the Nambu-Goto term, extrinsic curvature action and the Euler characteristic of the string world sheet.

hep-th↗

Special properties of a submanifold of su(3)

The finite gauge transformation, in the submanifold of su(3) introduced in hep-th/9902027, is found to be linear in the gauge functions $ω^a$'s. In this manner, a parameterization of SU(3) in terms of a single real octet vector $ω^a$ is achieved. Under this finite transformation, those gauge fields satisfying $D^{ab}_μω^b = 0$, remain unchanged. A geometric meaning to the submanifold in terms of rotations in E8 is presented.

hep-th↗

Infrared region of QCD and confinement

Gauge field configurations appropriate for the infrared region of QCD are proposed. Using the usual QCD action, confinement is realized as in the London theory of Meissner effect.

hep-th↗

Induced Rigid String Action From Fermions

From the Dirac action on the world sheet, an effective action is obtained by integrating over the 4-dimensional fermion fields pulled back to the world sheet. This action consists of the Nambu-Goto area term with right dimensionful constant in front, extrinsic curvature action and the topological Euler characteristic term.

hep-th↗

Current flow past an etched barrier: field emission from a two-dimensional electron gas

We find that, under appropriate conditions, electrons can pass a barrier etched across a two dimensional electron gas (2DEG) by field emission from the GaAs/AlGaAs heterojunction into a second, low-density 2DEG formed deep in the substrate. The current-voltage characteristics exhibit a rapid increase in the current at the field emission threshold and intrinsic bistability above this threshold, consistent with a heating instability occurring in the second 2DEG. These results may explain similar behaviour recently seen in a number of front-gated devices by several groups.

cond-mat.mes-hall↗

Modification of black-hole entropy by strings

A generalized action for strings which is a sum of the Nambu-Goto and the extrinsic curvature (the energy integral of the surface) terms, is used to couple strings to gravity. It is shown that the conical singularity has deficit angle that has contributions from both the above terms. It is found that the effect of extrinsic curvature is to oppose that of the N-G action for the temperature of the black-hole and to modify the entropy-area relation.

hep-th↗

String Theory In Curved Space-Time

Intrinsic and extrinsic geometric properties of string world sheets in curved space-time background are explored. In our formulation, the only dynamical degrees of freedom of the string are its immersion coordinates. Classical equation of motion and the space-time energy-momentum tensor of the string are obtained. The equations of motion for the extrinsic curvature action are second order for the scalar mean curvature of the world sheet. 1-loop divergent terms are calculated using the background field method. Asymptotic freedom of the extrinsic curvature coupling is established.

hep-th↗

Planckian Scattering From Kerr Black Holes: Eikonal and Beyond

Planckian scattering of particles with angular momenta is studied by describing them as sources of Kerr metric. In the shock wave formalism, it is found that the angular momenta do not contribute to the scattering amplitude in the eikonal limit. This is confirmed by using the wave equation of the test particle in the Kerr background.

hep-th↗