arXiv subjects

M. B. Paranjape

Publications and source records attributed to M. B. Paranjape.

71 records · Page 4Linked to original sources

arXiv1999

Topological symmetry breaking and confinement of anyons

We study the behaviour of Wilson and 't Hooft loop operators for the 2+1 dim. Abelian-Higgs model with Chern-Simons term. The phase of topological symmetry breaking where the vortex field condenses, found by Samuel for the model in the absence of the Chern-Simons term, persists in its presence. In this phase, the topological linking of instantons, which are configurations of closed vortex loops, with the Wilson loop on one hand and with the 't Hooft loop on the other hand gives rise to a long-range, logarithmic, confining potential between electric charges and magnetic flux tubes. This is surprising since the gauge field is short range due to the Chern-Simons term. Gauss' law forces the concomitance of charge and magnetic flux, hence the confinement is actually of anyons.

hep-th↗

arXiv1999

Causal Structure of Vacuum Solutions to Conformal(Weyl) Gravity

Using Penrose diagrams the causal structure of the static spherically symmetric vacuum solution to conformal (Weyl) gravity is investigated. A striking aspect of the solution is an unexpected physical singularity at $r=0$ caused by a linear term in the metric. We explain how to calculate the deflection of light in coordinates where the metric is manifestly conformal to flat i.e. in coordinates where light moves in straight lines.

astro-ph↗

arXiv1998

Recent mathematical developments in the Skyrme model

In this review we present a pedagogical introduction to recent, more mathematical developments in the Skyrme model. Our aim is to render these advances accessible to mainstream nuclear and particle physicists. We start with the static sector and elaborate on geometrical aspects of the definition of the model. Then we review the instanton method which yields an analytical approximation to the minimum energy configuration in any sector of fixed baryon number, as well as an approximation to the surfaces which join together all the low energy critical points. We present some explicit results for B=2. We then describe the work done on the multibaryon minima using rational maps, on the topology of the configuration space and the possible implications of Morse theory. Next we turn to recent work on the dynamics of Skyrmions. We focus exclusively on the low energy interaction, specifically the gradient flow method put forward by Manton. We illustrate the method with some expository toy models. We end this review with a presentation of our own work on the semi-classical quantization of nucleon states and low energy nucleon-nucleon scattering.

hep-th↗

arXiv1998

Classical tests for Weyl gravity: deflection of light and time delay

Weyl gravity has been advanced in the recent past as an alternative to General Relativity (GR). The theory has had some success in fitting galactic rotation curves without the need for copious amounts of dark matter. To check the viability of Weyl gravity, we propose two additional classical tests of the theory: the deflection of light and time delay in the exterior of a static spherically symmetric source. The result for the deflection of light is remarkably simple: besides the usual positive (attractive) Einstein deflection of $4GM/r_{0}$ we obtain an extra deflection term of $-γr_{0}$ where $γ$ is a constant and $r_0$ is the radius of closest approach. With a negative $γ$, the extra term can increase the deflection on large distance scales (galactic or greater) and therefore imitate the effect of dark matter. Notably, the negative sign required for $γ$ is opposite to the sign of $γ$ used to fit galactic rotation curves. The experimental constraints show explicitly that the magnitude of $γ$ is of the order of the inverse Hubble length something already noted by Mannheim and Kazanas as an interesting numerical coincidence in the fitting of galactic rotation curves.

astro-ph↗

arXiv1997

Localized Mass and Spin Sources in 2+1 Dimensional Topologically Massive Gravity

Stationary solutions to the full non-linear topologically massive gravity (TMG) are obtained for localized sources of mass $m$ and spin $σ$. Our results show that the topological term induces spin and that the total spin J (which is the spin observed by an asymptotic observer) ranges from 0 to $σ+ \frac{m}μ(\frac{4π+m}{4π+2m})$ depending on the structure of the spin source (here $μ$ is the topological mass). We find that it is inconsistent to consider actual delta function mass and spin sources. In the point-like limit, however, we find no condition constraining $m$ and $σ$ contrary to a previous analysis by Clement.

gr-qc↗

arXiv1997

Solitons in a Baby-Skyrme model with invariance under area preserving diffeomorphisms

We study the properties of soliton solutions in an analog of the Skyrme model in 2+1 dimensions whose Lagrangian contains the Skyrme term and the mass term, but no usual kinetic term. The model admits a symmetry under area preserving diffeomorphisms. We solve the dynamical equations of motion analytically for the case of spinning isolated baryon type solitons. We take fully into account the induced deformation of the spinning Skyrmions and the consequent modification of its moment of inertia to give an analytical example of related numerical behaviour found by Piette et al.. We solve the equations of motion also for the case of an infinite, open string, and a closed annular string. In each case, the solitons are of finite extent, so called "compactons", being exactly the vacuum outside a compact region. We end with indications on the scattering of baby-Skyrmions, as well as some considerations as the properties of solitons on a curved space.

hep-ph↗

arXiv1995

Baby Skyrmion Strings

We provide analytical and numerical evidence of the existence of classically stable, string-like configurations in a 2+1 dimensional analog of the Skyrme model. The model contains a conserved topological charge usually called the baryon number. Our strings are non-topological solitons which have a constant baryon number per unit length. The energy per length containing one baryon is, however, less than the energy of an isolated baryon (radially symmetric ``baby Skyrmion") in a region of the parameter space, which suggests a degree of stability for our configurations. In a limiting case, our configuration saturates a Bogomolnyi-type bound and is degenerate in energy per baryon with the baby Skyrmion. In another limiting case, the energies are still degenerate but do not saturate the corresponding Bogomolnyi-type bound. Nonetheless, we expect the string to be stable here. Both limiting cases are solvable analytically.

hep-ph↗

arXiv1995

Spontaneous Symmetry Breaking and the Renormalization of the Chern-Simons Term

We calculate the one-loop perturbative correction to the coefficient of the \cs term in non-abelian gauge theory in the presence of Higgs fields, with a variety of symmetry-breaking structures. In the case of a residual $U(1)$ symmetry, radiative corrections do not change the coefficient of the \cs term. In the case of an unbroken non-abelian subgroup, the coefficient of the relevant \cs term (suitably normalized) attains an integral correction, as required for consistency of the quantum theory. Interestingly, this coefficient arises purely from the unbroken non-abelian sector in question; the orthogonal sector makes no contribution. This implies that the coefficient of the \cs term is a discontinuous function over the phase diagram of the theory.

hep-th↗

arXiv1995

LOW ENERGY NUCLEON-NUCLEON SCATTERING IN THE SKYRME MODEL

We present the study of the influence of the leading contribution from the kinetic energy of the Skyrme Lagrangian on the scattering of low energy nucleons. This classical kinetic energy for the 2-body system is computed using the product ansatz and is correct for low energy, well separated Skyrmions. We quantize the rotational degrees of freedom of the Skyrmions in order to give them the right spin and isospin values. We are then able to compute analytically the scattering angles for some angular momenta polarizations.

hep-ph↗

arXiv1994

On the Coleman-Hill Theorem

The Coleman-Hill theorem prohibits the appearance of radiative corrections to the topological mass (more precisely, to the parity-odd part of the vacuum polarization tensor at zero momentum) in a wide class of abelian gauge theories in 2+1 dimensions. We re-express the theorem in terms of the effective action rather than in terms of the vacuum polarization tensor. The theorem so restated becomes somewhat stronger: a known exception to the theorem, spontaneously broken scalar Chern-Simons electrodynamics, obeys the new non-renormalization theorem. Whereas the vacuum polarization {\sl does} receive a one-loop, parity-odd correction, this does not translate to a radiative contribution to the Chern-Simons term in the effective action. We also point out a new situation, involving scalar fields and parity-odd couplings, which was overlooked in the original analysis, where the conditions of the theorem are satisfied and where the topological mass does, in fact, get a radiative correction.

hep-th↗

arXiv1994

Low Energy Skyrmion-Skyrmion Scattering

We study the scattering of Skyrmions at low energy and large separation using the method proposed by Manton of truncation to a finite number of degrees freedom. We calculate the induced metric on the manifold of the union of gradient flow curves, which for large separation, to first non-trivial order is parametrized by the variables of the product ansatz. (presented at the Lake Louise Winter Institute, 1994)

hep-ph↗

arXiv1994

Low Energy Nucleon-Nucleon Scattering with the Skyrme Model in the Geodetic Approximation

We calculate nucleon-nucleon scattering at low energies and large impact parameter in the Skyrme model within the framework for soliton scattering proposed by Manton. This corresponds to a truncation of the degrees of freedom to the twelve collective coordinates which essentially describe the rigid body motion of the pair of Skyrmions. We take to its logical conclusion the result that the induced kinetic energy for these collective coordinates in the product ansatz behaves as one over the separation and hence can dominate over the potential. This behaviour implies to leading order that we can drop the potential and the resulting motion reduces simply to geodesic motion on the manifold parametrized by the variables of the product ansatz. We formulate the semi-classical quantization of these variables to obtain the motion corresponding to the nucleonic states of the Skyrme model. This is the appropriate description for the nucleons in order to consider their scattering within Manton's framework in the semi-classical approximation. We investigate the implications for the scattering of nucleons with various initial polarizations using the approximation method of ``variation of constants''.

hep-ph↗

arXiv1994

Low Energy Skyrmion-Skyrmion Scattering

We study the scattering of two Skyrmions at low energy and large separation. We use the method proposed by Manton for truncating the degrees of freedom of the system from infinite to a manageable finite number. This corresponds to identifying the manifold consisting of the union of the low energy critical points of the potential along with the gradient flow curves joining these together and by positing that the dynamics is restricted here. The kinetic energy provides an induced metric on this manifold while restricting the full potential energy to the manifold defines a potential. The low energy dynamics is now constrained to these finite number of degrees of freedom. For large separation of the two Skyrmions the manifold is parametrised by the variables of the product ansatz. We find the interaction between two Skyrmions coming from the induced metric, which was independently found by Schroers. We find that the static potential is actually negligible in comparison to this interaction. Thus to lowest order, at large separation, the dynamics reduces to geodesic motion on the manifold. We consider the scattering to first order in the interaction using the perturbative method of Lagrange and find that the dynamics in the no spin or charge exchange sector reduces to the Kepler problem.

hep-th↗

arXiv1993

Skyrmion-Skyrmion Scattering

We study the scattering of Skyrmions at low energy and large separation using the method proposed by Manton of truncation to a finite number of degree freedom. We calculate the induced metric on the manifold of the union of gradient flow curves, which for large separation, to first non-trivial order is parametrised by the variables of the product ansatz.

hep-th↗

arXiv1993

Delicacies of the Mass Perturbation in the Schwinger Model on a Circle

The Hilbert bundle for the massless fermions of the Schwinger model on a circle, over the space of gauge field configurations, is topologically non-trivial (twisted). The corresponding bundle for massive fermions is topologically trivial (periodic). Since the structure of the fermionic Hilbert bundle changes discontinuously the possibility of perturbing in the mass is thrown into doubt. In this article, we show that a direct application of the anti-adiabatic theorem of Low, allows the structure of the massless theory to be dynamically preserved in the strong coupling limit, ${e\over m}>>1$. This justifies the use of perturbation theory in the bosonized version of the model, in this limit.

hep-th↗

arXiv1993

Violations of the String Hypothesis in the Solutions of the Bethe Ansatz Equations in the XXX-Heisenberg

We study the equations for the quasi-momenta which characterize the wave-functions in the Bethe ansatz for the XXX-Heisenberg model. We show in a simple analytical fashion, that the usual ``string hypothesis" incorrectly predicts the number of real solutions and the number of complex solutions for $N>21$ in the sector with two spins flipped, confirming the work of Essler et al. Two complex pair solutions drop out and form two additional real pair solutions. We also introduce a new set of variables which allows the equations to be written as a single polynomial equation in one variable. We consider in some detail the case of three spins flipped.

hep-th↗

arXiv1993

Instantons and the Ground State of the Massive Schwinger Model

We study the massive Schwinger model, quantum electrodynamics of massive, Dirac fermions, in 1+1 dimensions; with space compactified to a circle. In the limit that transitions to fermion--anti-fermion pairs can be neglected, we study the full ground state. We focus on the effect of instantons which mediate tunnelling transitions in the induced potential for the dynamical degree of freedom in the gauge field.

hep-th↗