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V. P. Nair

Publications and source records attributed to V. P. Nair.

At least 19 recordsLinked to original sources
arXiv2026

Higher dimensional quantum Hall effect and the analog of $W_\infty$-algebra

We show that Abelian and nonabelian gauge transformations are the analog of $W_\infty$ transformations for higher dimensional quantum Hall effect. The commutator anomaly and the extended algebra of such transformations on the edge modes of a droplet are obtained by purely topological arguments, basically utilizing the two-cocycle in the descent procedure for anomalies and using the fact that there is anomaly cancellation between the bulk and boundary actions. The method relies on the fact that bulk actions are easily constructed in general using the Dolbeault index theorem. The resulting algebras are shown to agree with explicit edge mode calculations for cases where they are available. We also comment on the similarities and differences in the nature of these transformations between two and higher dimensions.

hep-th↗
arXiv2026

A Note on Coadjoint Orbits for Multifermion Systems

The coadjoint orbit action for a multifermion system, as an exact description of its dynamics, is considered. A parametrization of the variables involved is given which facilitates the approximation of this by another coadjoint orbit action suitable for expansions around the Fermi surface, recovering various actions which have been used in previous literature. The presentation of this in terms of functions on phase space with star-products as well as further truncations are briefly considered.

hep-th↗
arXiv2026

Time-dependent Magnetic Fields and the Quantum Hall Effect

Ermakov has shown how the solution to the classical harmonic oscillator in one spatial dimension with general time-dependent frequency can be reduced to the time-independent case and an associated nonlinear ordinary differential equation, an analysis which has been applied to the Schrödinger equation as well. We extend this analysis to the Landau problem of a charged particle in a uniform magnetic field in two dimensions and construct the generalized Laughlin wave functions for the case when the magnetic field is time-dependent. We also work out the dynamics of density fluctuations (the Girvin, MacDonald, Platzman or GMP mode) and argue that it is possible to tune the frequency of the magnetic field to obtain a compressible droplet of fermions. We also analyze the dynamics of the edge modes of the droplet for the integer Hall effect.

cond-mat.mes-hall↗
arXiv2026

On Quantum Field Theory and Observers

A generalization of the coadjoint orbit action describes the dynamics of an observer (or instrument). We consider how this fits in with the view of observables in field theory being correlations of read-outs of instruments and show how one recovers the usual $S$-matrix formulae. A simple resolution of the Fermi paradox is also pointed out.

hep-th↗
arXiv2025

On Casimir effect in Yang-Mills theories in three and four dimensions

We calculate the Casimir energy for the configuration of two parallel plates coupled to nonabelian gauge fields with a Yang-Mills action. We consider both 2+1 and 3+1 dimensions in the manifestly gauge-invariant formalism we have pursued over the last several years which allows us to factor out the gauge degrees of freedom. A boundary action in the functional integral, equivalent to the insertion of operators representing the plates, is used to enforce the required boundary conditions for the gauge fields. The result is for a kinematic regime corresponding to the exchange of gluons with a dynamically generated mass. We find good agreement in 2+1 dimensions and reasonable agreement in 3+1 dimensions with lattice-based numerical evaluations.

hep-th↗
arXiv2025

A.P. Balachandran: Living in Physics

A.P. Balachandran was a theoretical physicist of extraordinary versatility and originality. In a career spanning over six decades, he made many significant contributions to quantum field theory and mathematical physics. His influence extends beyond the impact of his papers, with a large number of research students and collaborators. Here, in an attempt at a coherent scientific biography, I try to contextualize and evaluate his many contributions.

physics.hist-ph↗
arXiv2025

Spectral functions at nonzero temperature

We present a straightforward derivation of the spectral representation of a scalar field at nonzero temperature, assuming that the field is relativistically invariant in vacuum. This form was first derived by Bros and Buchholz.

hep-th↗
arXiv2025

Fractional quantum Hall effect in higher dimensions

Generalizing from previous work on the integer quantum Hall effect, we construct the effective action for the analog of Laughlin states for the fractional quantum Hall effect in higher dimensions. The formalism is a generalization of the parton picture used in two spatial dimensions, the crucial ingredient being the cancellation of anomalies for the gauge fields binding the partons together. Some subtleties which exist even in two dimensions are pointed out. The effective action is obtained from a combination of the Dolbeault and Dirac index theorems. We also present expressions for some transport coefficients such as Hall conductivity and Hall viscosity for the fractional states.

hep-th↗
arXiv2024

Entanglement and Interface Conditions on Fields

We consider the vacuum wave function of a free scalar field theory in space partitioned into two regions, with the field obeying Robin conditions (of parameter $κ$) on the interface. A direct integration over fields in a subregion is carried out to obtain the reduced density matrix. This leads to a constructive proof of the Reeh-Schlieder theorem. We analyze the entanglement entropy as a function of the Robin parameter $κ$. We also consider a specific conditional probability as another measure of entanglement which is more amenable to analysis of the dependence on interface conditions. Finally, we discuss a direct calculation of correlation functions and how it gives an alternate route to the reduced density matrix.

hep-th↗
arXiv2024

A Note on Coherent States for Virasoro Orbits

There are two sets of orbits of the Virasoro group which admit a Kähler structure. We consider the construction of coherent states for the orbit $\widehat{{\rm diff}\,S^1}$/$SL(2, {\mathbb R})$ which furnishes unitary representations of the group. The procedure is analogous to geometric quantization using a holomorphic polarization. We also give an explicit formula for the Kähler potential for this orbit and comment on normalization of the coherent states. We further explore some of the properties of these states, including the definition of symbols corresponding to operators and their star products. Some comments which touch upon the possibility of applying this to gravity in (2+1) dimensions are also given.

hep-th↗
arXiv2024

Topological fluids with boundaries and fractional quantum Hall edge dynamics: A fluid dynamics derivation of the chiral boson action

This paper investigates the bulk and boundary dynamics of Laughlin states, which are modeled using composite boson theory within a fluid dynamics framework. In this work, we adopt an alternative starting point based on a hydrodynamic action with topological terms, which fleshes out the fluid aspects of the Laughlin state manifestly. For a particular choice of the velocity field, the fluid equation for this action is akin to first-order hydrodynamic equations, supplemented with an additional constitutive equation known as the Hall constraint. When a hard wall boundary is present, one of the topological terms in the fluid action triggers anomaly inflow, indicating the presence of gauge anomaly at the edge. The first-order hydrodynamic equations require a second boundary condition which, in the absence of dissipation, can be either a no-slip or a no-stress condition. We find that the no-slip condition, where the fluid adheres to the wall is incompatible with the chiral edge dynamics. On the other hand, the no-stress condition, which allows the fluid to move along the wall without friction, is consistent with the expected chiral edge dynamics of the Laughlin state. Furthermore, our work derives this modified no-stress boundary condition within a variational principle. This is accomplished by incorporating a chiral boson action within the boundary action that is non-linearly coupled to the edge density, thus systematically extending the edge chiral Luttinger liquid theory.

cond-mat.mes-hall↗
arXiv2023

Fractional topological charge in $SU(N)$ gauge theories without dynamical quarks

In $SU(N)$ gauge theories without dynamical quarks, we discuss how configurations with fractional topological charge, $\sim 1/N$, can arise in the vacuum and dominate in the confining phase. They are not solutions of the classical equations of motion, but arise as quantum solutions of the effective Lagrangian. Their size is essentially fixed, on the order of the confinement scale. We give both a general mathematical analysis and illustrative solutions. Their presence can be measured through numerical simulations on the lattice using known methods. As they carry $\mathbb{Z}_N$ magnetic charge, the introduction of dynamical quarks significantly complicates their dynamics.

hep-th↗
arXiv2023

The Schrödinger Representation and 3d Gauge Theories

In this review we consider the Hamiltonian analysis of Yang-Mills theory and some variants of it in three spacetime dimensions using the Schrödinger representation. This representation, although technically more involved than the usual covariant formulation, may be better suited for some nonperturbative issues. Specifically for the Yang-Mills theory, we explain how to set up the Hamiltonian formulation in terms of manifestly gauge-invariant variables and set up an expansion scheme for solving the Schrödinger equation. We review the calculation of the string tension, the Casimir energy and the propagator mass and compare with the results from lattice simulations. The computation of the first set of corrections to the string tension, string breaking effects, extensions to the Yang-Mills-Chern-Simons theory and to the supersymmetric cases are also discussed. We also comment on how entanglement for the vacuum state can be formulated in terms of the BFK gluing formula. The review concludes with a discussion of the status and prospects of this approach.

hep-th↗
arXiv2023

Transport coefficients for higher dimensional quantum Hall effect

An effective action for the bulk dynamics of quantum Hall effect in arbitrary even spatial dimensions was obtained some time ago in terms of a Chern-Simons term associated with the Dolbeault index theorem. Here we explore further properties of this action, showing how electronic band structures can be incorporated, obtaining Hall currents and conductivity (for arbitrary dimensions) in terms of integrals of Chern classes for the bands. We also derive the expression for Hall viscosity from the effective action. Explicit formulae for the Hall viscosity are given for 2+1 and 4+1dimensions.

cond-mat.mes-hall↗
arXiv2022

Gauge and Scalar Fields on $\mathbb{CP}^2$: A Gauge-invariant Analysis I. The effective action from chiral scalars

A parametrization of gauge fields on complex projective spaces of arbitrary dimension is given as a generalization of the two-dimensional case. Gauge transformations act homogeneously on the fields, facilitating a manifestly gauge-invariant analysis. Specializing to four dimensions, we consider the nature of the effective action due to chiral scalars interacting with the gauge fields. The key qualitatively significant terms include a possible gauge-invariant mass term and a finite four-dimensional Wess-Zumino-Witten (WZW) action. We comment on relating the mass term to lattice simulations as well as Schwinger-Dyson analyses, and also on relating the WZW action to the instanton liquid picture of QCD.

hep-th↗
arXiv2022

Gauge and Scalar Fields on $\mathbb{CP}^2$: A Gauge-invariant Analysis II. The measure for gauge fields and a 4d WZW theory

We consider the volume of the gauge orbit space for gauge fields on four-dimensional complex projective space. The analysis uses a parametrization of gauge fields where gauge transformations act homogeneously on the fields, facilitating a manifestly gauge-invariant analysis. The volume element contains a four-dimensional Wess-Zumino-Witten (WZW) action for a hermitian matrix-valued field. There is also a mass-like term for certain components of the gauge field. We discuss how the mass term could be related to results from lattice simulations as well as Schwinger-Dyson equations. We argue for a kinematic regime where the Yang-Mills theory can be approximated by the 4d-WZW theory. The result is suggestive of the instanton liquid picture of QCD. Further it is also indicative of the mechanism for confinement being similar to what happens in two dimensions.

hep-th↗
arXiv2022

Eductions of Edge Mode Effects

Edge modes in gauge theories, whose raison d'etre is in the nature of the test functions used for imposing the Gauss law, have implications in many physical contexts. I discuss two such cases: 1) how edge modes are related to the interface term in the BFK formula and how they generate the so-called contact term for entanglement entropy in gauge theories, 2) how they describe the dynamics of particles in generalizing the Einstein-Infeld-Hoffmann approach to particle dynamics in theories of gravity.

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