arXiv subjects

Nabamita Banerjee

Publications and source records attributed to Nabamita Banerjee.

At least 37 records · Page 2Linked to original sources

arXiv2020

Classical Soft Theorem in the AdS-Schwarzschild spacetime in small cosmological constant limit

We have studied scattering of a probe particle by a four dimensional AdS-Schwarzschild black hole at large impact factor. Our analysis is consistent perturbatively to leading order in the AdS radius and black hole mass parameter. Next we define a proper "soft limit" of the radiation and extract out the "soft factor" from it. We find the correction to the well known flat space Classical Soft graviton theorem due to the presence of an AdS background.

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arXiv2020

Bhargava's Cube and Black Hole Charges

Black holes in a class of string compactifications, known as STU models, carry four electric and four magnetic charges. Furthermore a duality group, given by the product of three congruence subgroups of $SL(2,\mathbb{Z})$, acts on these integer valued charges. By placing these eight charges at the eight corners of a Bhargava cube, we provide a classification of the duality orbits in these theories.

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arXiv2019

New N=2 SuperBMS$_3$ algebra and Invariant Dual Theory for 3D Supergravity

We have constructed a two dimensional theory dual to 3D asymptotically flat Supergravity in presence of two supercharges with(out) internal $R-$symmetry. The duals in both the cases are identified with chiral Wess-Zumino-Witten models. Further gauging the theories, we show that the dual of the one without $R-$symmetry is invariant under the well known ${\cal{N}}=2$ SuperBMS$_3$ introduced in Banerjee et.al. 1609.09210 , while for the one with $R-$symmetry, the dual is invariant under the most generic, so far unknown, quantum ${\cal{N}}=2$ SuperBMS$_3$ symmetry. We have also commented on the phase space description of the duals.

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arXiv2019

Equivalent Dual Theories for 3D N=2 Supergravity

N=2 three dimensional Supergravity with internal $R-$symmetry generators can be understood as a two dimensional chiral Wess-Zumino-Witten model. In this paper, we present the reduced phase space description of the theory, which turns out to be flat limit of a generalised Liouville theory, up to zero modes. The reduced phase space description can also be explained as a gauged chiral Wess-Zumino-Witten model. We show that both these descriptions possess identical gauge and global (quantum N=2 superBMS$_3$) symmetries.

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arXiv2019

Maximally $\cal{N}$-extended super-BMS$_3$ algebras and Generalized 3D Gravity Solutions

We consider the maximal $\cal{N}-$extended supergravity theory in 3 dimensions with fermionic generators transforming under real but non necessarily irreducible representations of the internal algebra. We obtain the symmetry algebra at null infinity preserving boundary conditions of asymptotically flat solutions, i.e. the maximal $\cal{N}-$extended super-BMS$_3$ algebra, which possesses non-linear correction in the anti-commutators of supercharges. We present the supersymmetric energy bound and derive the explicit form of the asymptotic Killing spinors. We also find the most generic circular symmetric ground state of the theory, which corresponds to a non-supersymmetric cosmological solutions and derive their entropy.

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arXiv2018

Conformal Structure of Massless Scalar Amplitudes Beyond Tree level

We show that the one-loop on-shell four-point scattering amplitude of massless $ϕ^4$ scalar field theory in 4D Minkowski space time, when Mellin transformed to the Celestial sphere at infinity, transforms covariantly under the global conformal group ($SL(2,C)$) on the sphere. The unitarity of the four-point scalar amplitudes is recast into this Mellin basis. We show that the same conformal structure also appears for the two-loop Mellin amplitude. Finally we comment on some universal structure for all loop four-point Mellin amplitudes specific to this theory.

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arXiv2018

N=4 Supersymmetric BMS3 algebras from asymptotic symmetry analysis

We consider three dimensional $N=4$ flat supergravity, with an abelian R-symmetry enhancing the gravitational phase space. We obtain the field configuration whose asymptotic symmetries at null infinity coincide with the centrally extended $N=4$ super Bondi-Metzner-Sachs (BMS) algebra .The killing spinors for this generic configuration are obtained together with the energy bounds imposed by supersymmetry. It is explicitly shown that the same algebra can be obtained as a flat (AdS radius $\rightarrow \infty$ ) limit of the combined $(2,0)$ and $(0,2)$ sectors of AdS supergravity.

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arXiv2017

Second order Galilean fluids & Stokes' law

We study the second derivative effects on the constitutive relations of an uncharged parity-even Galilean fluid using the null fluid framework. Null fluids are an equivalent representation of Galilean fluids in terms of a higher dimensional relativistic fluid, which makes the Galilean symmetries manifest and tractable. The analysis is based on the offshell formalism of hydrodynamics. We use this formalism to work out a generic algorithm to obtain the constitutive relations of a Galilean fluid up to arbitrarily high derivative orders, and later specialise to second order. Finally, we study the Stokes' law which determines the drag force on an object moving through a fluid, in presence of certain second order terms. We identify the second order transport coefficients which leave the drag force invariant.

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arXiv2016

First Order Galilean Superfluid Dynamics

We study dynamics of (anomalous) Galilean superfluid up to first order in derivative expansion, both in parity-even and parity-odd sectors. We construct a relativistic system -- null superfluid, which is a null fluid (introduced in [arXiv:1509.04718]) with a spontaneously broken global $U(1)$ symmetry. A null superfluid is in one to one correspondence with Galilean superfluid in one lower dimension, i.e. they have same symmetries, thermodynamics, constitutive relations and are related to each other by a mere choice of basis. The correspondence is based on null reduction, which is known to reduce the Poincaré symmetry of a theory to Galilean symmetry in one lower dimension. To perform this analysis, we use offshell formalism of (super)fluid dynamics, adopting it appropriately to null (super)fluids.

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arXiv2016

Extended Supersymmetric BMS$_3$ algebras and Their Free Field Realisations

We study $N=(2,4,8)$ supersymmetric extensions of the three dimensional BMS algebra (BMS$_3$) with most generic possible central extensions. We find that $N$-extended supersymmetric BMS$_3$ algebras can be derived by a suitable contraction of two copies of the extended superconformal algebras. Extended algebras from all the consistent contractions are obtained by scaling left-moving and right-moving supersymmetry generators symmetrically, while Virasoro and R-symmetry generators are scaled asymmetrically. On the way, we find that the BMS/GCA correspondence does not in general hold for supersymmetric systems. Using the $β$-$γ$ and the ${\mathfrak b}$-${\mathfrak c}$ systems, we construct free field realisations of all the extended super-BMS$_3$ algebras.

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arXiv2016

Free-field realisations of the BMS$_3$ algebra and its extensions

We construct an explicit realisation of the BMS$_3$ algebra with nonzero central charges using holomorphic free fields. This can be extended by the addition of chiral matter to a realisation having arbitrary values for the two independent central charges. Via the introduction of additional free fields, we extend our construction to the minimally supersymmetric BMS$_3$ algebra and to the nonlinear higher-spin BMS$_3$-W$_3$ algebra. We also describe an extended system that realises both the SU(2) current algebra as well as BMS$_3$ via the Wakimoto representation, though in this case introducing a central extension also brings in new non-central operators.

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arXiv2016

The Resolution of an Entropy Puzzle for 4D non-BPS Black Holes

We show the equality between macroscopic and microscopic black hole entropy for a class of four dimensional non-supersymmetric black holes in ${\cal N}=2$ supergravity theory, up to the first subleading order in their charges. This solves a long standing entropy puzzle for this class of black holes. The macroscopic entropy has been computed in the presence of a newly derived higher-derivative supersymmetric invariant of \cite{Butter:2013lta}, connected to the five dimensional supersymmetric Weyl squared Lagrangian. Microscopically, the crucial role in obtaining the equivalence is played by the anomalous gauge gravitational Chern-Simons term.

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arXiv2016

The off-shell c-map

The off-shell version of the c-map is presented, based on a systematic off-shell reduction from four to three space-time dimensions for supergravity theories with eight supercharges. In the reduction, the R-symmetry group is enhanced to local [SU(2) x SU(2)]/Z2 =SO(4) and the c-map is effected by a parity transformation in the internal space that interchanges the two SU(2) factors. Vector and tensor supermultiplets are each others conjugate under the c-map and both can be dualized in three dimensions to (on-shell) hypermultiplets. As shown in this paper the off-shell formulation indeed leads to a clarification of many of the intricate issues that play a role in the c-map. The results for off-shell Lagrangians quadratic in space-time derivatives are analyzed in detail and compared to the literature. The underlying reasons are identified why not all of the four-dimensional tensor multiplet Lagrangians can be in the image of the c-map. The advantage of the off-shell approach is, that it also enables a systematic analysis of theories with higher-derivative couplings. This is demonstrated for a particular subclass of such theories, which, under certain conditions, are consistent under the c-map. In principle, explicit results for realistic four-dimensional type-II string compactifications can be explored in this way.

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arXiv2015

Equilibrium partition function for nonrelativistic fluids

We construct an equilibrium partition function for a non-relativistic fluid and use it to constrain the dynamics of the system. The construction is based on light cone reduction, which is known to reduce the Poincare symmetry to Galilean in one lower dimension. We modify the constitutive relations of a relativistic fluid, and find that its symmetry broken phase - `null fluid' is equivalent to the non-relativistic fluid. In particular, their symmetries, thermodynamics, constitutive relations, and equilibrium partition function match exactly to all orders in derivative expansion.

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arXiv2015

Null Fluids - A New Viewpoint of Galilean Fluids

This article is a detailed version of our short letter `On equilibrium partition function for non-relativistic fluid' [arXiv:1505.05677] extended to include an anomalous $U(1)$ symmetry. We construct a relativistic system, which we call null fluid and show that it is in one-to-one correspondence with a Galilean fluid living in one lower dimension. The correspondence is based on light cone reduction, which is known to reduce the Poincare symmetry of a theory to Galilean in one lower dimension. We show that the proposed null fluid and the corresponding Galilean fluid have exactly same symmetries, thermodynamics, constitutive relations, and equilibrium partition to all orders in derivative expansion. We also devise a mechanism to introduce $U(1)$ anomaly in even dimensional Galilean theories using light cone reduction, and study its effect on the constitutive relations of a Galilean Fluid.

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arXiv2015

Higher Derivative Corrections to Charged Fluids in 2n Dimensions

We study anomalous charged fluid in $2n$-dimensions ($n\geq 2$) up to sub-leading derivative order. Only the effect of gauge anomaly is important at this order. Using the Euclidean partition function formalism, we find the constraints on different sub-leading order transport coefficients appearing in parity-even and odd sectors of the fluid. We introduce a new mechanism to count different fluid data at arbitrary derivative order. We show that only the knowledge of independent scalar-data is sufficient to find the constraints. In appendix we further extend this analysis to obtain fluid data at sub-sub-leading order (where both gauge and gravitational anomaly contribute) for parity-odd fluid.

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arXiv2014

Entropy current for non-relativistic fluid

We study transport properties of a parity-odd, non-relativistic charged fluid in presence of background electric and magnetic fields. To obtain stress tensor and charged current for the non-relativistic system we start with the most generic relativistic fluid, living in one higher dimension and reduce the constituent equations along the light-cone direction. We also reduce the equation satisfied by the entropy current of the relativistic theory and obtain a consistent entropy current for the non-relativistic system (we call it "canonical form" of the entropy current). Demanding that the non-relativistic fluid satisfies the second law of thermodynamics we impose constraints on various first order transport coefficients. For parity even fluid, this is straight forward; it tells us positive definiteness of different transport coefficients like viscosity, thermal conductivity, electric conductivity etc. However for parity-odd fluid, canonical form of the entropy current fails to confirm the second law of thermodynamics. Therefore, we need to add two parity-odd vectors to the entropy current with arbitrary coefficients. Upon demanding the validity of second law, we see that one can fix these two coefficients exactly.

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arXiv2013

Chern-Simons Superconductor

We study the effect of a bulk Chern-Simons (CS) term on 3+1 dimensional type II superconductor in the context of the AdS/CFT correspondence. We holographically compute the super-current and find that it is non-local in nature. It receives non trivial corrections due to presence of the CS term. Considering a large limit of a parameter "lambda" (we call this limit as long wave length limit), which is effectively the high temperature limit of the theory, we find that this non-local super-current boils down to a local quantity. The leading term (without the CS term) of this current matches with the result of Ginzburg-Landau (GL) theory. We compute the effect of the CS term on GL current and find that the effect is highly suppressed at large temperature (~1/T^4). Finally, free energy of the vortex configuration has been calculated. The free energy also receives non trivial correction at the order of 1/lambda^2 in the long wave length approximation.

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