Publications (141)396.48 Total impact
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ABSTRACT: We study generic twodimensional dilaton gravity with a Maxwell field and prove its triviality for constant dilaton boundary conditions, despite of the appearance of a Virasoro algebra with nonzero central charge. We do this by calculating the canonical boundary charges, which turn out to be trivial, and by calculating the quantum gravity partition function, which turns out to be unity. We show that none of the following modifications changes our conclusions: looser boundary conditions, nonlinear interactions of the Maxwell field with the dilaton, inclusion of higher spin fields, inclusion of generic gauge fields. Finally, we consider specifically the charged JackiwTeitelboim model, whose holographic study was pioneered by Hartman and Strominger, and show that it is nontrivial for certain linear dilaton boundary conditions. We calculate the entropy from the Euclidean path integral, using Wald's method and exploiting the chiral Cardy formula. The macroscopic and microscopic results for entropy agree with each other.  [Show abstract] [Hide abstract]
ABSTRACT: We analyze the Casimir interaction of doped graphene. To this end we derive a simple expression for the finite temperature polarization tensor with a chemical potential. It is found that doping leads to a strong enhancement of the Casimir force reaching almost $60\%$ in quite realistic situations. This result should be important for planning and interpreting the Casimir measurements, especially taking into account that the Casimir interaction of undoped graphene is rather weak. 
Article: Nonassociative Weyl star products
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ABSTRACT: Deformation quantization is a formal deformation of the algebra of smooth functions on some manifold. In the classical setting, the Poisson bracket serves as an initial conditions, while the associativity allows to proceed to higher orders. Some applications to string theory require deformation in the direction of a quasiPoisson bracket (that does not satisfy the Jacobi identity). This initial conditions is incompatible with associativity, it is quite unclear which restrictions can be imposed on the deformation. We show that for any quasiPoisson bracket the deformation quantization exists and is essentially unique if one requires (weak) hermiticity and the Weyl condition. We also propose an iterative procedure that allows to compute the star product up to any desired order.  [Show abstract] [Hide abstract]
ABSTRACT: We investigate whether inclusion of dimension six terms in the Standard Model lagrangean may cause the unification of the coupling constants at a scale comprised between 10^14 and 10^17 GeV. Particular choice of the dimension 6 couplings is motivated by the spectral action. Given the theoretical and phenomenological constraints, as well as recent data on the Higgs mass, we find that the unification is indeed possible, with a lower unification scale slightly favoured. 
Article: High energy bosons do not propagate
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ABSTRACT: We discuss the propagation of bosons (scalars, gauge fields and gravitons) at high energy in the context of the spectral action. Using heat kernel techniques, we find that in the highmomentum limit the quadratic part of the action does not contain positive powers of the derivatives. We interpret this as the fact that the twopoint Green functions vanish for nearby points, where the proximity scale is given by the inverse of the cutoff. (C) 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license  [Show abstract] [Hide abstract]
ABSTRACT: We provide a holographic description of twodimensional dilaton gravity with Antide Sitter boundary conditions. We find that the asymptotic symmetry algebra consists of a single copy of the Virasoro algebra with nonvanishing central charge and point out difficulties with the standard canonical treatment. We generalize our results to higher spin theories and thus provide the first examples of twodimensional higher spin gravity with holographic description. For spin3 gravity we find that the asymptotic symmetry algebra is a single copy of the W_3algebra.  [Show abstract] [Hide abstract]
ABSTRACT: We consider gated graphene nanoribbons subject to BerryMondragon boundary conditions in the presence of weak impurities. Using fieldtheoretical methods, we calculate the density of charge carriers (and, thus, the quantum capacitance) as well as the optical and DC conductivities at zero temperature. We discuss in detail their dependence on the gate (chemical) potential, and reveal a nonlinear behaviour induced by the quantization of the transversal momentum.  [Show abstract] [Hide abstract]
ABSTRACT: Poisson sigma models are a very rich class of twodimensional theories that includes, in particular, all 2D dilaton gravities. By using the Hamiltonian reduction method, we show that a Poisson sigma model (with a sufficiently wellbehaving Poisson tensor) on a finite cylinder is equivalent to a noncommutative quantum mechanics for the boundary data.  [Show abstract] [Hide abstract]
ABSTRACT: We propose Lobachevsky boundary conditions that lead to asymptotically H^2xR solutions. As an example we check their consistency in conformal ChernSimons gravity. The canonical charges are quadratic in the fields, but nonetheless integrable, conserved and finite. The asymptotic symmetry algebra consists of one copy of the Virasoro algebra with central charge c=24k, where k is the ChernSimons level, and an affine u(1). We find also regular nonperturbative states and show that none of them corresponds to black hole solutions. We attempt to calculate the oneloop partition function, find a remarkable separation between bulk and boundary modes, but conclude that the oneloop partition function is illdefined due to an infinite degeneracy. We comment on the most likely resolution of this degeneracy.  [Show abstract] [Hide abstract]
ABSTRACT: We compute the Casimir energy for a free scalar field on the spaces where is twodimensional deformed twosphere. 
Article: Faraday rotation in graphene
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ABSTRACT: We study magnetooptical properties of monolayer graphene by means of quantum field theory methods in the framework of the Dirac model. We reveal a good agreement between the Dirac model and a recent experiment on giant Faraday rotation in cyclotron resonance. We also predict other regimes when the effects are well pronounced. The general dependence of the Faraday rotation and absorption on various parameters of samples is revealed both for suspended and epitaxial graphene.  [Show abstract] [Hide abstract]
ABSTRACT: The principal object in noncommutatve geometry is the spectral triple consisting of an algebra A, a Hilbert space H, and a Dirac operator D. Field theories are incorporated in this approach by the spectral action principle, that sets the field theory action to Tr f(D^2/\Lambda^2), where f is a real function such that the trace exists, and \Lambda is a cutoff scale. In the lowenergy (weakfield) limit the spectral action reproduces reasonably well the known physics including the standard model. However, not much is known about the spectral action beyond the lowenergy approximation. In this paper, after an extensive introduction to spectral triples and spectral actions, we study various expansions of the spectral actions (exemplified by the heat kernel). We derive the convergence criteria. For a commutative spectral triple, we compute the heat kernel on the torus up the second order in gauge connection and consider limiting cases.  [Show abstract] [Hide abstract]
ABSTRACT: We compute a Chern–Simons term induced by the fermions on noncommutative torus interacting with two U(1) gauge fields. For rational noncommutativity θ∝P/Q we find a new mixed term in the action which involves only those fields which are (2π)/Q periodic, like the fields in a crystal with Q2 nodes. 
Article: Twist to close
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ABSTRACT: It has been proposed that the Poincaré and some other symmetries of noncommutative field theories should be twisted. Here we extend this idea to gauge transformations and find that twisted gauge symmetries close for arbitrary gauge group. We also analyse twistedinvariant actions in noncommutative theories. 
Article: Quantum Field Theory in Graphene
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ABSTRACT: This is a short nontechnical introduction to applications of the Quantum Field Theory methods to graphene. We derive the Dirac model from the tight binding model and describe calculations of the polarization operator (conductivity). Later on, we use this quantity to describe the Quantum Hall Effect, light absorption by graphene, the Faraday effect, and the Casimir interaction.  [Show abstract] [Hide abstract]
ABSTRACT: The spectral action for a noncompact commutative spectral triple is computed covariantly in a gauge perturbation up to order 2 in full generality. In the ultraviolet regime, $p\to\infty$, the action decays as $1/p^4$ in any even dimension.  [Show abstract] [Hide abstract]
ABSTRACT: In a $U(1)_{\star}$noncommutative (NC) gauge field theory we extend the SeibergWitten (SW) map to include the (gaugeinvarianceviolating) external current and formulate  to the first order in the NC parameter  gaugecovariant classical field equations. We find solutions to these equations in the vacuum and in an external magnetic field, when the 4current is a static electric charge of a finite size $a$, restricted from below by the elementary length. We impose extra boundary conditions, which we use to rule out all singularities, $1/r$ included, from the solutions. The static charge proves to be a magnetic dipole, with its magnetic moment being inversely proportional to its size $a$. The external magnetic field modifies the longrange Coulomb field and some electromagnetic formfactors. We also analyze the ambiguity in the SW map and show that at least to the order studied here it is equivalent to the ambiguity of adding a homogeneous solution to the currentconservation equation.  [Show abstract] [Hide abstract]
ABSTRACT: It has been argued, that in noncommutative field theories sizes of physical objects cannot be taken smaller than an elementary length related to noncommutativity parameters. By gaugecovariantly extending field equations of noncommutative U(1)_*theory to the presence of external sources, we find electric and magnetic fields produces by an extended charge. We find that such a charge, apart from being an ordinary electric monopole, is also a magnetic dipole. By writing off the existing experimental clearance in the value of the lepton magnetic moments for the present effect, we get the bound on noncommutativity at the level of 10^4 TeV.  [Show abstract] [Hide abstract]
ABSTRACT: The graviton 1loop partition function is calculated for Euclidean generalised massive gravity (GMG) using AdS heat kernel techniques. We find that the results fit perfectly into the AdS/(L)CFT picture. Conformal ChernSimons gravity, a singular limit of GMG, leads to an additional contribution in the 1loop determinant from the conformal ghost. We show that this contribution has a nice interpretation on the conformal field theory side in terms of a semiclassical null vector at level two descending from a primary with conformal weights (3/2,1/2).  [Show abstract] [Hide abstract]
ABSTRACT: We adopt the Dirac model for quasiparticles in graphene and calculate the finite temperature Casimir interaction between a suspended graphene layer and a parallel conducting surface. We find that at high temperature the Casimir interaction in such system is just one half of that for two ideal conductors separated by the same distance. In this limit single graphene layer behaves exactly as a Drude metal. In particular, the contribution of the TE mode is suppressed, while one of the TM mode saturates the ideal metal value. Behaviour of the Casimir interaction for intermediate temperatures and separations accessible for an experiment is studied in some detail. We also find an interesting interplay between two fundamental constants of graphene physics: the fine structure constant and the Fermi velocity.
Publication Stats
3k  Citations  
396.48  Total Impact Points  
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Institutions

20092014

Universidade Federal do ABC (UFABC)
Santo André, São Paulo, Brazil


2013

Universidade Federal de São Paulo
San Paulo, São Paulo, Brazil


20072011

University of São Paulo
 São Carlos Institute of Physics
San Paulo, São Paulo, Brazil 
Dnepropetrovsk National University
Yekaterinoslav, Dnipropetrovs'ka Oblast', Ukraine


19922011

Saint Petersburg State University
SanktPeterburg, St.Petersburg, Russia


19982007

University of Leipzig
 Institute of Theoretical Physics
Leipzig, Saxony, Germany


20022003

Max Planck Institute for Mathematics in the Sciences
Leipzig, Saxony, Germany 
Max Planck Institute for Mathematics
Bonn, North RhineWestphalia, Germany


19961998

Vienna University of Technology
 Institute of Theoretical Physics
Wien, Vienna, Austria


1994

Tokyo Institute of Technology
 Department of Physics
Edo, Tokyo, Japan


19921994

Abdus Salam International Centre for Theoretical Physics
Trst, Friuli Venezia Giulia, Italy


19891991

Leningrad State University
SanktPeterburg, St.Petersburg, Russia
