arXiv subjects

N. E. Mavromatos

Publications and source records attributed to N. E. Mavromatos.

At least 127 records · Page 7Linked to original sources

arXiv1998

World-Sheet Defects, Strings, and Quark Confinement

In this talk I give a preliminary account of original results, obtained in collaboration with John Ellis. Details and further elaboration will be presented in a forthcoming publication. We present a proposal for a non-critical (Liouville) string approach to confinement of four-dimensional (non-abelian) gauge theories, based on recent developments on the subject by Witten and Maldacena. We discuss the effects of vortices and monopoles on the open world-sheets whose boundaries are Wilson loops of the target-space (non Abelian) Gauge theory. By appropriately employing `D-particles', associated with the target-space embedding of such defects, we argue that the apprearance of five-dimensional Anti-De-Sitter (AdS) space times is quite natural, as a result of Liouville dressing.We isolate the world-sheet defect contributions to the Wilson loop by constructing an appropriate observable, which is the same as the second observable in the supersymmetric U(1) theory of Awada and Mansouri, but in our approach supersymmetry is not necessary.When vortex condensation occurs, we argue in favour of a (low-temperature) confining phase, in the sense of an area law, for a large-$N_c$ (conformal) gauge theory at finite temperatures. A connection of the Berezinski-Kosterlitz-Thouless (BKT) transitions on the world-sheet with the critical temperatures in the thermodynamics of Black Holes in the five-dimensional AdS space is made.

hep-th↗

arXiv1998

Dynamical Flavour Symmetry Breaking by a Magnetic Field in Lattice QED_3

We perform a lattice study, in the quenched approximation, of dynamical mass generation in a system of relativistic (Dirac) fermions, coupled to an Abelian gauge field in (2+1)-dimensions, in the presence of an external (constant) magnetic field, perpendicular to the spatial planes. It is shown that a strong magnetic field catalyzes chiral symmetry breaking, in agreement with results in the continuum. The rôle of the higher-Landau poles in inducing a critical temperature above which the phenomenon disappears is pointed out. We also discuss the implications of this model on the opening of a gap in doped antiferromagnetic superconductors.

hep-lat↗

arXiv1998

Ferroelectrics and their possible involvement in Biology

We present the main properties of ferroelectricity, with emphasis given to a specific family of hydrated ferroelectric crystals, which can serve as model systems for corresponding configurations in biology like the microtubules. An experimental method is described, which allows to establish the ferroelectric property of microtubules in suspension.

quant-ph↗

arXiv1998

Quantum Mechanics in Cell Microtubules: Wild Imagination or Realistic Possibility?

We focus on potential mechanisms for `energy-loss-free' transport along the cell microtubules, which could be considered as realizations of Fröhlich's ideas on the role of solitons for superconductivity and/or biological matter. In particular, by representing the MT arrangements as `cavities',we present a novel scenario on the formation of macroscopic (or mesoscopic) quantum-coherent states, as a result of the (quantum-electromagnetic) interactions of the MT dimers with the surrounding molecules of the ordered water in the interior of the MT cylinders. We present some generic order of magnitude estimates of the decoherence time in a typical model for MT dynamics. The role of (conjectured) ferroelectric properties of MT arrangements on the above quantum phenomena is emphasized. Based on these considerations, we also present a conjecture on the role of the MT in `holographic' information processing, which resembles the situation encountered in internal source X-ray holography in atomic physics.

quant-ph↗

arXiv1998

Induced Magnetic moments in three-dimensional gauge theories with external magnetic fields

We study the appearance of induced parity-violating magnetic moment, in the presence of external magnetic fields, for even-number of fermion species coupled to dynamical fields in three dimensions. Specifically, we use a SU(2)xU(1) gauge model for dynamical gauge symmetry breaking, which is also proposed recently as a field theoretical model for high-temperature superconductors. By decomposing the fermionic degrees of freedom in terms of Landau levels, we show that, in the effective theory with the lowest Landau levels, a parity-violating magnetic moment interaction is induced by the higher Landau levels when the fermions are massive. The possible relevance of this result for a recently observed phenomenon in high-temperature superconductors is also discussed.

hep-th↗

arXiv1997

Irreversible Time Flow in a Two-Dimensional Dilaton Black Hole with Matter

We show that an exact solution of two-dimensional dilaton gravity with matter discovered previously exhibits an irreversible temporal flow towards flat space with a vanishing cosmological constant. This time flow is induced by the back reaction of matter on the space-time geometry. We demonstrate that the system is not in equilibrium if the cosmological constant is non-zero, whereas the solution with zero cosmological constant is stable. The flow of the system towards this stable end-point is derived from the renormalization-group flow of the Zamolodchikov function. This behaviour is interpreted in terms of non-critical Liouville string, with the Liouville field identified as the target time.

gr-qc↗

arXiv1997

N=1 Supersymmetric Spin-Charge Separation in effective gauge theories of planar magnetic superconductors

We present a N=1 Supersymmetric extension of a spin-charge separated effective $SU(2)\times U_S(1)$ `particle-hole' gauge theory of excitations about the nodes of the gap of a d-wave planar magnetic superconductor. The supersymmetry is achieved without introducing extra degrees of freedom, as compared to the non-supersymmetric models. The only exception, the introduction of gaugino fieds, finds a natural physical interpretation as describing interlayer coupling in the statistical model. The low-energy continuum theory is described by a relativistic (2+1)-dimensional supersymmetric $CP^1$ $σ$-model with Gross-Neveu-Thirring-type four-fermion interactions. We emphasize the crucial rôle of the $CP^1$ constraint in inducing a non-trivial dynamical mass generation for fermions (and thus superconductivity), in a way compatible with manifest N=1 supersymmetry. We also give a preliminary discussion of non-perturbative effects. We argue that supersymmetry suppresses the dangerous for superconductivity instanton contributions to the mass of the perturbatively massless gauge boson of the unbroken U(1) subgroup of SU(2). Finally, we point out the possibility of applying these ideas to effective gauge models of spin-charge separation in one-space dimensional superconducting chains of holons, which, for example, have recently been claimed to be important in the stripe phase of underdoped cuprates.

cond-mat↗

arXiv1997

Decoherent Scattering of Light Particles in a D-Brane Background

We discuss the scattering of two light particles in a D-brane background. It is known that, if one light particle strikes the D brane at small impact parameter, quantum recoil effects induce entanglement entropy in both the excited D brane and the scattered particle. In this paper we compute the asymptotic `out' state of a second light particle scattering off the D brane at large impact parameter, showing that it also becomes mixed as a consequence of quantum D-brane recoil effects. We interpret this as a non-factorizing contribution to the superscattering operator S-dollar for the two light particles in a Liouville D-brane background, that appears when quantum D-brane excitations are taken into account.

hep-th↗

arXiv1997

T duality for boundary-non-critical strings

Recent work on the action of T duality on Dirichlet-branes is generalized to the case in which the open string satisfies boundary conditions that are neither Neumann nor Dirichlet. This is achieved by implementing T duality as a canonical transformation of the $σ$-model path integral. A class of boundary interactions that violate conformal symmetry is found to be T-dual of a correspondingly non-conformal class of boundary conditions. The analogy with some problems in boundary-non-critical quantum mechanics of interest for condensed matter is pointed out.

hep-th↗

arXiv1997

Matrix Sigma-models for Multi D-brane Dynamics

We describe a dynamical worldsheet origin for the Lagrangian describing the low-energy dynamics of a system of parallel D-branes. We show how matrix-valued collective coordinate fields for the D-branes naturally arise as couplings of a worldsheet sigma-model, and that the quantum dynamics require that these couplings be mutually noncommutative. We show that the low-energy effective action for the sigma-model couplings describes the propagation of an open string in the background of the multiple D-brane configuration, in which all string interactions between the constituent branes are integrated out and the genus expansion is taken into account, with a matrix-valued coupling. The effective field theory is governed by the non-abelian Born-Infeld target space action which leads to the standard one for D-brane field theory.

hep-th↗

arXiv1997

Gauge-theory approach to planar doped antiferromagnets and external magnetic fields

A review is given of a relativistic non-Abelian gauge theory approach to the physics of spin-charge separation in doped quantum antiferromagnetic planar systems, proposed recently by the authors. Emphasis is put on the effects of constant external magnetic fields on excitations about the superconducting state in the model. The electrically-charged Dirac fermions (holons), describing excitations about specific points on the fermi surface, e.g. those corresponding to the nodes of a d-wave superconducting gap in high-$T_c$ cuprates, condense, resulting in the opening of a Kosterlitz-Thouless-like gap (KT) at such nodes. In the presence of strong external magnetic fields at the surface regions of the planar superconductor, in the direction perpendicular to the superconducting planes, these KT gaps appear to be enhanced. Our preliminary analysis, based on analytic Scwhinger-Dyson treatments, seems to indicate that for an even number of Dirac fermion species, required in our model as a result of gauging a particle-hole SU(2) symmetry, Parity or Time Reversal violation does not necessarily occurs.Based on these considerations, we argue that recent experimental findings, concerning thermal conductivity plateaux of quasiparticles in planar high-$T_c$ cuprates in strong external magnetic fields, may indicate the presence of such KT gaps, caused by charged Dirac-fermion excitations in these materials, as suggested in the above model.

cond-mat↗

arXiv1997

On Quantum Mechanical Aspects of Microtubules

We discuss possible quantum mechanical aspects of MicroTubules (MT), based on recent developments in quantum physics.We focus on potential mechanisms for `energy-loss-free' transport along the microtubules, which could be considered as realizations of Fröhlich's ideas on the rôle of solitons for superconductivity and/or biological matter. By representing the MT arrangements as cavities,we present a novel scenario on the formation of macroscopic (or mesoscopic) quantum-coherent states, as a result of the (quantum-electromagnetic) interactions of the MT dimers with the surrounding molecules of the ordered water in the interior of the MT cylinders. We suggest specific experiments to test the above-conjectured quantum nature of the microtubular arrangements inside the cell. These experiments are similar in nature to those in atomic physics, used in the detection of the Rabi-Vacuum coupling between coherent cavity modes and atoms. Our conjecture is that a similar Rabi-Vacuum-splitting phenomenon occurs in the MT case.

quant-ph↗

arXiv1997

Dynamical Gauge Symmetry Breaking and Superconductivity in three-dimensional systems

We discuss dynamical breaking of non-abelian gauge groups in three dimensional (lattice) gauge systems via the formation of fermion condensates. A physically relevant example, motivated by condensed-matter physics, is that of a fermionic gauge theory with group $SU(2)\otimes U_S(1) \otimes U_{E}(1)$. In the strong U_S(1) region, the SU(2) symmetry breaks down to a U(1), due to the formation of a parity-invariant fermion condensate. We conjecture a phase diagram for the theory involving a critical line, which separates the regions of broken SU(2) symmetry from those where the symmetry is restored. In the broken phase, the effective Abelian gauge theory is closely related to an earlier model of two-dimensional parity-invariant superconductivity in doped antiferromagnets. The superconductivity in the model occurs in the Kosterlitz-Thouless mode, since strong phase fluctuations prevent the existence of a local order parameter. Some physical consequences of the $SU(2) \times U_S(1)$ phase diagram for the (doping-dependent) parameter space of this condensed-matter model are briefly discussed.

hep-lat↗

arXiv1997

Hidden Non-Abelian Gauge Symmetries in Doped Planar Antiferromagnets

We investigate the possibility of hidden non-Abelian Local Phase symmetries in large-U doped planar Hubbard antiferromagnets, believed to simulate the physics of two-dimensional (magnetic) superconductors. We present a spin-charge separation ansatz, appropriate to incorporate holon spin flip, which allows for such a hidden local gauge symmetry to emerge in the effective action. The group is of the form $SU(2)\otimes U_S(1) \otimes U_E(1)$, where SU(2) is a local non-Abelian group associated with the spin degrees of freedom, U_E(1) is that of ordinary electromagnetism, associated with the electric charge of the holes, and U_S(1) is a `statistical' Abelian gauge group pertaining to the fractional statistics of holes on the spatial plane. In a certain regime of the parameters of the model, namely strong U_S(1) and weak SU(2), there is the possibility of dynamical formation of a holon condensate. This leads to a dynamical breaking of $SU(2) \to U(1)$. The resulting Abelian effective theory is closely related to an earlier model proposed as the continuum limit of large-spin planar doped antiferromagnets, which lead to an unconventional scenario for two-dimensional parity-invariant superconductivity.

cond-mat↗

arXiv1997

Vacuum Fluctuations and Decoherence in Mesoscopic and Microscopic Systems

We discuss recent experimental evidence of decoherence in a laboratory mesoscopic system in a cavity, from which we draw analogies with the decoherence that we argue is induced by microscopic quantum-gravity fluctuations in the space-time background. We emphasize the parallel rôles played in both cases by dissipation through non-trivial vacuum fluctuations that trigger the collapse of an initially coherent quantum state. We review a phenomenological parametrization of possible effects of this kind in the neutral kaon system, where they would induce CPT violation, and describe some epxerimental tests.

quant-ph↗

arXiv1997

M Theory from World-Sheet Defects in Liouville String

We have argued previously that black holes may be represented in a D-brane approach by monopole and vortex defects in a sine-Gordon field theory model of Liouville dynamics on the world sheet. Supersymmetrizing this sine-Gordon system, we find critical behaviour in 11 dimensions, due to defect condensation that is the world-sheet analogue of D-brane condensation around an extra space-time dimension in M theory. This supersymmetric description of Liouville dynamics has a natural embedding within a 12-dimensional framework suggestive of F theory.

hep-th↗

arXiv1997

Quantum Decoherence in a D-Foam Background

Within the general framework of Liouville string theory, we construct a model for quantum D-brane fluctuations in the space-time background through which light closed-string states propagate. The model is based on monopole and vortex defects on the world sheet, which have been discussed previously in a treatment of 1+1-dimensional black-hole fluctuations in the space-time background, and makes use of a T-duality transformation to relate formulations with Neumann and Dirichlet boundary conditions. In accordance with previous general arguments, we derive an open quantum-mechanical description of this D-brane foam which embodies momentum and energy conservation and small mean energy fluctuations. Quantum decoherence effects appear at a rate consistent with previous estimates.

hep-th↗

arXiv1997

Dilatonic Black Holes in Higher-Curvature String Gravity II: Linear Stability

We demonstrate linear stability of the dilatonic Black Holes appearing in a string-inspired higher-derivative gravity theory with a Gauss- Bonnet curvature-squared term. The proof is accomplished by mapping the system to a one-dimensional Schrodinger problem which admits no bound states. This result is important in that it constitutes a linearly stable example of a black hole that bypasses the `no-hair conjecture'. However, the dilaton hair is `secondary'in the sense that it is not accompanied by any new quantum number for the black hole solution.

hep-th↗