arXiv subjects

Rakibur Rahman

Publications and source records attributed to Rakibur Rahman.

27 records · Page 2Linked to original sources

arXiv2012

Higher-Spin Fermionic Gauge Fields and Their Electromagnetic Coupling

We study the electromagnetic coupling of massless higher-spin fermions in flat space. Under the assumptions of locality and Poincare invariance, we employ the BRST-BV cohomological methods to construct consistent parity-preserving off-shell cubic 1-s-s vertices. Consistency and non-triviality of the deformations not only rule out minimal coupling, but also restrict the possible number of derivatives. Our findings are in complete agreement with, but derived in a manner independent from, the light-cone-formulation results of Metsaev and the string-theory-inspired results of Sagnotti-Taronna. We prove that any gauge-algebra-preserving vertex cannot deform the gauge transformations. We also show that in a local theory, without additional dynamical higher-spin gauge fields, the non-abelian vertices are eliminated by the lack of consistent second-order deformations.

hep-th↗

arXiv2011

Notes on a Cure for Higher-Spin Acausality

We present a Lagrangian describing a massive charged spin-2 field and a scalar in a constant electromagnetic background, and we provide a consistent description of the system. The Lagrangian, derived from string field theory through a suitable dimensional reduction, propagates the correct number of degrees of freedom within the light cone in any space-time dimension less than 26. We briefly discuss the higher-spin generalization of this construction, that cures the pathologies of a massive charged particle of arbitrary integer spin by introducing only finitely many new massive degrees of freedom.

hep-th↗

arXiv2011

String Theory and The Velo-Zwanziger Problem

We examine the behavior of the leading Regge trajectory of the open bosonic string in a uniform electromagnetic background and present a consistent set of Fierz-Pauli conditions for these symmetric tensors that generalizes the Argyres-Nappi spin-2 result. These equations indicate that String Theory does bypass the Velo-Zwanziger problem, i.e. the loss of causality experienced by a massive high-spin field minimally coupled to electromagnetism. Moreover, we provide some evidence that only the first Regge trajectory can be described in isolation and show that the open-string spectrum is free of ghosts in weak constant backgrounds. Finally, we comment on the roles of the critical dimension and of the gyromagnetic ratio.

hep-th↗

arXiv2010

Gauge gravity duality for d-wave superconductors: prospects and challenges

We write down an action for a charged, massive spin two field in a fixed Einstein background. Despite some technical problems, we argue that in an effective field theory framework and in the context of the AdS/CFT correspondence, this action can be used to study the properties of a superfluid phase transition with a d-wave order parameter in a dual strongly interacting field theory. We investigate the phase diagram and the charge conductivity of the superfluid phase. We also explain how possible couplings between the spin two field and bulk fermions affect the fermion spectral function.

hep-th↗

arXiv2010

Consequences of Gravity-Induced Couplings in Theories with Many Particle Species

In theories with many copies of the Standard Model virtual black hole exchange may produce effective higher dimensional operators that can be treated below the cutoff scale as fundamental vertices of interspecies non-gravitational interaction. We consider the vertex that couples fermions of one species through magnetic moment to photons of other species, and study the quantum corrections it generates. In particular, we find kinetic mixing between photons of different species produced via fermion loops. Diagonalization of gauge kinetic terms then renders the fermions millicharged under other species' electromagnetism. We explore some phenomenological consequences of such effects by considering possible observable signatures in collider experiments and constraining the interaction strength. The derived bounds are in agreement with non-democratic nature of micro black hole coupling.

hep-ph↗

arXiv2009

Causal Propagation of a Charged Spin 3/2 Field in an External Electromagnetic Background

We present a Lagrangian for a massive, charged spin 3/2 field in a constant external electromagnetic background, which correctly propagates only physical degrees of freedom inside the light cone. The Velo-Zwanziger acausality and other pathologies such as loss of hyperbolicity or the appearance of unphysical degrees of freedom are avoided by a judicious choice of non-minimal couplings. No additional fields or equations besides the spin 3/2 ones are needed to solve the problem.

hep-th↗

arXiv2009

A Model Independent Ultraviolet Cutoff for Theories with Charged Massive Higher Spin Fields

We argue that the theory of a massive higher spin field coupled to electromagnetism in flat space possesses an intrinsic, model independent, finite upper bound on its UV cutoff. By employing the Stueckelberg formalism we do a systematic study to quantify the degree of singularity of the massless limit in the cases of spin 2, 3, 3/2, and 5/2. We then generalize the results for arbitrary spin to find an expression for the maximum cutoff of the theory as a function of the particle's mass, spin, and electric charge. We also briefly explain the physical implications of the result and discuss how it could be sharpened by use of causality constraints.

hep-th↗

arXiv2008

Electromagnetically Interacting Massive Spin-2 Field: Intrinsic Cutoff and Pathologies in External Fields

By employing the Stueckelberg formalism, we argue that the theory of massive spin-2 field coupled to electromagnetism in flat space must have an intrinsic, model independent, finite UV cutoff. We show how the very existence of a cutoff has connection to other pathologies of the system, such as superluminal propagation. We comment on the generalization of the results to arbitrary spin, and to gravitational interaction.

hep-th↗

arXiv2006

Domain Walls As Probes Of Gravity

We show that domain walls are probes that enable one to distinguish large-distance modified gravity from general relativity (GR) at short distances. For example, low-tension domain walls are stealth in modified gravity, while they do produce global gravitational effects in GR. We demonstrate this by finding exact solutions for various domain walls in the DGP model. A wall with tension lower than the fundamental Planck scale does not inflate and has no gravitational effects on a 4D observer, since its 4D tension is completely screened by gravity itself. We argue that this feature remains valid in a generic class of models of infrared modified gravity. As a byproduct, we obtain exact solutions for super-massive codimension-2 branes.

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