Kumar Abhinav

Supersymmetry, PT-symmetry and spectral bifurcation

We demonstrate that large class of PT-symmetric complex potentials, which can have isospectral real partner potentials, possess two different superpotentials. In the parameter domain, where the superpotential is unique, the spectrum is real and shape-invariant, leading to translational shift in a suitable parameter by real units. The case of two different superpotentials, leading to same potential, yields broken PT-symmetry, the energy spectra in the two phases being separated by a bifurcation. Interestingly, these two superpotentials generate the two disjoint sectors of the Hilbert space. In the broken case, shape invariance produces complex parametric shifts.Abstract We demonstrate that large class of PT-symmetric complex potentials, which can have isospectral real partner potentials, possess two different superpotentials. In the parameter domain, where the superpotential is unique, the spectrum is real and shape-invariant, leading to translational shift in a suitable parameter by real units. The case of two different superpotentials, leading to same potential, yields broken PT-symmetry, the energy spectra in the two phases being separated by a bifurcation. Interestingly, these two superpotentials generate the two disjoint sectors of the Hilbert space. In the broken case, shape invariance produces complex parametric shifts.

Gapped solitons and periodic excitations in strongly coupled BECs

It is found that localized solitons in the strongly coupled cigar-shaped Bose–Einstein condensates (BECs), in the repulsive domain, form two distinct classes. The one without a background is an asymptotically vanishing, localized soliton, having a wave number, which has a lower bound in magnitude. Periodic soliton trains exist only in the presence of a background, where the localized soliton has a W-type density profile. This soliton is well suited for trapping of neutral atoms and is found to be stable under Vakhitov–Kolokolov criterion, as well as numerical evolution. We identify an insulating phase of this system in the presence of an optical lattice. It is demonstrated that the W-type density profile can be precisely controlled through trap dynamics.

Quasi-integrability in supersymmetric sine-Gordon models

The deformed supersymmetric sine-Gordon model, obtained through known deformation of the corresponding potential, is found to be quasi-integrable, like its non-supersymmetric counterpart, which was observed earlier. The system expectedly possesses finite number of conserved quantities, leaving-out an infinite number of non-conserved anomalous charges. The quasi-integrability of this supersymmetric model heavily rely on the boundary conditions of the potential, otherwise rendered to be completely non-integrable. Moreover, interesting additional algebraic structures appear, absent in the non-supersymmetric counterparts.

Novel symmetries in Weyl-invariant gravity with massive gauge field

The background field method is used to linearize the Weyl-invariant scalar–tensor gravity, coupled with a Stückelberg field. For a generic background metric, this action is found not to be invariant, under both a diffeomorphism and generalized Weyl symmetry, the latter being a combination of gauge and Weyl transformations. Interestingly, the quadratic Lagrangian, emerging from a background of Minkowski metric, respects both transformations independently. The Becchi–Rouet–Stora–Tyutin symmetry of scalar–tensor gravity coupled with a Stückelberg-like massive gauge particle, possessing a diffeomorphism and generalized Weyl symmetry, reveals that in both cases negative-norm states with unphysical degrees of freedom do exist. We then show that, by combining diffeomorphism and generalized Weyl symmetries, all the ghost states decouple, thereby removing the unphysical redundancies of the theory. During this process, the scalar field does not represent any dynamic mode, yet modifies the usual harmonic gauge condition through non-minimal coupling with gravity.

Conservation law for massive scale-invariant photons in Weyl-invariant gravity

It is demonstrated that a Stueckelberg-type gauge theory, coupled to the scalar-tensor theory of gravity, is invariant under both gauge and Weyl transformations. Unlike the pure Stueckelberg theory, this coupled Lagrangian has a genuine Weyl symmetry, with a non-vanishing current. The above is true in the Jordan frame, whereas in the Einstein frame, the same theory manifests as Proca theory in presence of pure gravity. It is found that broken scale invariance leads to simultaneous spontaneous breaking of the gauge symmetry.

Quantum and thermal fluctuations and pair-breaking in planar QED

A bstractPlanar quantum electrodynamics, in presence of tree-level Chern-Simons term, is shown to support bound state excitations, with a threshold, not present for the pure Chern-Simons theory. In the present case, the bound state gets destabilized by vacuum fluctuations. The bound state itself finds justification in the duality of the theory with massive topological vector field. Thermal fluctuations further destabilize this state, leading to smooth dissociation at high temperatures. Physical systems are suggested for observing such a bound state.

Heisenberg symmetry and collective modes of one dimensional unitary correlated fermions

Abstract The correlated fermionic many-particle system, near infinite scattering length, reveals an underlying Heisenberg symmetry in one dimension, as compared to an S O ( 2 , 1 ) symmetry in two dimensions. This facilitates an exact map from the interacting to the non-interacting system, both with and without a harmonic trap, and explains the short-distance scaling behavior of the wave-function. Taking advantage of the phenomenological Calogero–Sutherland-type interaction, motivated by the density functional approach, we connect the ground-state energy shift, to many-body correlation effect. For the excited states, modes at integral values of the harmonic frequency ω are predicted in one dimension, in contrast to the breathing modes with frequency 2ω in two dimensions.

Solitons and spin transport in graphene boundary

It is shown that in (2 + 1)-dimensional condensed matter systems, induced gravitational Chern–Simons (CS) action can play a crucial role for coherent spin transport in a finite geometry, provided zero-curvature condition is satisfied on the boundary. The role of the resultant KdV solitons is explicated. The fact that KdV solitons can pass through each other without interference, represent ‘resistanceless’ spin transport.