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N. E. Mavromatos

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

At least 73 records · Page 4Linked to original sources
arXiv2003

Novel Phases and Old Puzzles in QED3 and related models

In this review we discuss novel phases (quantum critical points occurring only for T=0) in (2+1)-dimensional Abelian gauge theories, which may serve as prototypes for studying the physics of nodal excitations in (underdoped) high temperature superconductors. We pay particular attention to describing the existence of novel phases related to the anomalous breaking of certain symmetries, including unconventional superconducting properties. Although some of the results are rather old, we present them here from a physical perspective not discussed previously in the literature. In this respect we also explore the (in)applicability of some non perturbative approaches on the existence of a critical number of fermion flavours for chiral symmetry breaking in our specific models, which is an issue closely related to the existence of the novel phases mentioned above.

cond-mat.str-el↗
arXiv2003

Novel type of CPT violation for correlated EPR states

We discuss modifications to the concept of an ``antiparticle'', induced by a breakdown of the CPT symmetry at a fundamental level, realized within an extended class of quantum gravity models. The resulting loss of particle-antiparticle identity in the neutral-meson system induces a breaking of the EPR correlation imposed by Bose statistics. The latter is parametrized by a complex parameter controlling the amount of contamination by the ``wrong'' symmetry state. The physical consequences are studied, and novel observables of CPT-violation in $ϕ$ factories are proposed.

hep-ph↗
arXiv2003

WMAPing the Universe: Supersymmetry, Dark Matter, Dark Energy, Proton Decay and Collider Physics

In this review we discuss constraints on minimal supersymmetric models of particle physics implied by the recent astrophysical observations of WMAP. Although the prospects of detecting supersymmetry increase and 90 percent of the available MSSM parameter space can safely be reached by the sensitivity of future colliders, nevertheless we pay particular emphasis on discussing regions of the appropriate phase diagrams, which -if realized - would imply that detection of supersymmetry, at least in the context of minimal models, could be out of colliders reach. We also discuss the importance of a precise determination of the radiative corrections to the muon anomalous magnetic moment, both theoretically and experimentally. Finally, we briefly commend upon recent evidence, supported by observations, on a dark energy component of the Universe, of as yet unknown origin, covering 73 percent of its energy content.

hep-ph↗
arXiv2003

Super Heavy Dark Matter Anisotropies from D-particles in the Early Universe

We discuss a way of producing anisotropies in the spectrum of superheavy Dark matter, which are due to the distortion of the inflationary space time induced by the recoil of D-particles upon their scattering with ordinary string matter in the Early Universe. We calculate such distortions by world-sheet Liouville string theory (perturbative) methods. The resulting anisotropies are found to be proportional to the average recoil velocity and density of the D-particles. In our analysis we employ a regulated version of de Sitter space, allowing for graceful exit from inflation. This guarantees the asymptotic flatness of the space time, as required for a consistent interpretation, within an effective field theory context, of the associated Bogolubov coefficients as particle number densities. The latter are computed by standard WKB methods.

hep-th↗
arXiv2003

Towards Exact Results in Nodal Antiferromagnetic Planar Liquids

It has been argued in previous works by the authors that nodal excitations in (2+1)-dimensional doped antiferromagnets might exhibit, in the spin-charge separation framework and at specific regions of the parameter space, a supersymmetry between spinons and holons. This supersymmetry has been elevated to a N=2 extended supersymmetry of composite operators of spinon and holons, corresponding to the effective "hadronic" degrees of freedom. In this work we elaborate further on this idea by describing in some detail the dynamics of a specific composite model corresponding to an Abelian Higgs model (SQED). The abelian nature of the gauge group seems to be necessitated both by the composite structure used, but also by electric charge considerations for the various composites. We demonstrate the passage from a pseudogap to an unconventional superconducting phase, which notably is an exact non-perturbative analytic result, due to the underlying N=2 supersymmetric Abelian gauge theory. We believe that these considerations may provide a first step towards a non-perturbative understanding of the phase diagrams of strongly-correlated electron systems.

cond-mat.supr-con↗
arXiv2003

Quantum-Gravity Analysis of Gamma-Ray Bursts using Wavelets

In some models of quantum gravity, space-time is thought to have a foamy structure with non-trivial optical properties. We probe the possibility that photons propagating in vacuum may exhibit a non-trivial refractive index, by analyzing the times of flight of radiation from gamma-ray bursters (GRBs) with known redshifts. We use a wavelet shrinkage procedure for noise removal and a wavelet `zoom' technique to define with high accuracy the timings of sharp transitions in GRB light curves, thereby optimizing the sensitivity of experimental probes of any energy dependence of the velocity of light. We apply these wavelet techniques to 64 ms and TTE data from BATSE, and also to OSSE data. A search for time lags between sharp transients in GRB light curves in different energy bands yields the lower limit $M \ge 6.9 \cdot 10^{15}$ GeV on the quantum-gravity scale in any model with a linear dependence of the velocity of light $~ E/M$. We also present a limit on any quadratic dependence.

astro-ph↗
arXiv2003

Impact of Low-Energy Constraints on Lorentz Violation

We extend previous analyses of the violation of Lorentz invariance induced in a non-critical string model of quantum space-time foam, discussing the propagation of low-energy particles through a distribution of non-relativistic D-particles.We argue that nuclear and atomic physics experiments do not constitute sensitive probes of this approach to quantum gravity due to a difference in the dispersion relations for massive probes as compared to those for massless ones, predicted by the model.

gr-qc↗
arXiv2002

Vacuum Energy, Cosmological Supersymmetry Breaking and Inflation from Colliding Brane Worlds

In the context of colliding brane worlds I discuss a toy cosmological model, developed in collaboration with E. Gravanis, which arguably produces inflation and a relaxing to zero cosmological ``constant'' hierarchically small as compared to the supersymmetry breaking (TeV) scale. Supersymmetry breaking is induced by compactification of the brane worlds on magnetized tori. The crucial ingredient is the non-criticality (non conformality) of string theory on the observable brane world induced at the collision, which is thus viewed as a cause for departure from equilibrium in this system. The hierarchical smallness of the present-era vacuum energy, as compared to the SUSY breaking scale, is thus attributed to relaxation.

hep-th↗
arXiv2002

Induced N=2 composite supersymmetry in 2+1 dimensions

Starting from N=1 scalar supermultiplets in 2+1 dimensions, we build explicitly the composite superpartners which define a N=2 superalgebra induced by the initial N=1 supersymmetry. The occurrence of this extension is linked to the topologically conserved current out of which the composite superpartners are constructed.

hep-th↗
arXiv2002

Acceleration of the Universe in Type-0 Non-Critical Strings: a Review

I review cosmology within the framework of type-0 non-critical strings, proposed in collaboration with G. Diamandis, B. Georgalas, E. Papantonopoulos and I. Pappa. The instabilities of the tachyonic backgrounds, due to the absence of space-time supersymmetry, are treated in this framework as a necessary ingredient to ensure cosmological flow. The model involves D3 brane worlds, whose initial quantum fluctuations induce the non criticality. I argue that this model is compatible with the current astrophysical observations pointing towards acceleration of the Universe. A crucial rôle for the correct ``phenomenology'' of the model, in particular the order-one value of the deceleration parameter, is played by the relative magnitude of the flux of the five form of the type-0 string as compared to the size of the volume of five of the extra dimensions, transverse to the direction of the flux-field.

hep-th↗
arXiv2002

QED-Cavity model of microtubules implies dissipationless energy transfer and biological quantum teleportation

We refine a QED-cavity model of microtubules (MTs), proposed earlier by two of the authors (N.E.M. and D.V.N.), and suggest mechanisms for the formation of biomolecular mesoscopic coherent and/or entangled quantum states, which may avoid decoherence for times comparable to biological characteristic times. This refined model predicts dissipationless energy transfer along such "shielded" macromolecules at near room temperatures as well as quantum teleportation of states across MTs and perhaps neurons.

quant-ph↗
arXiv2002

Acceleration of the Universe in Type-0 Non-Critical Strings

Presently there is preliminary observational evidence that the cosmological constant might be non zero, and hence that our Universe is eternally accelerating (de Sitter). This poses fundamental problems for string theory, since a scattering matrix is not well defined in such Universes. In a previous paper we have presented a model, based on (non-equilibrium) non-critical strings, which is characterized by eventual ``graceful'' exit from a de Sitter phase. The model is based on a type-0 string theory, involving D3 brane worlds, whose initial quantum fluctuations induce the non criticality. We argue in this article that this model is compatible with the current observations. A crucial rôle for the correct ``phenomenology'' of the model is played by the relative magnitude of the flux of the five form of the type 0 string to the size of five of the extra dimensions, transverse to the direction of the flux-field. We do not claim, at this stage at least, that this model is a realistic physical model for the Universe, but we find it interesting that the model cannot be ruled out immediately, at least on phenomenological grounds.

hep-th↗
arXiv2001

Non-Critical Liouville String Escapes Constraints on Generic Models of Quantum Gravity

It has recently been pointed out that generic models of quantum gravity must contend with severe phenomenological constraints imposed by gravitational Cerenkov radiation, neutrino oscillations and the cosmic microwave background radiation. We show how the non-critical Liouville-string model of quantum gravity we have proposed escapes these constraints. It gives energetic particles subluminal velocities, obviating the danger of gravitational Cerenkov radiation. The effect on neutrino propagation is naturally flavour-independent, obviating any impact on oscillation phenomenology. Deviations from the expected black-body spectrum and the effects of time delays and stochastic fluctuations in the propagation of cosmic microwave background photons are negligible, as are their effects on observable spectral lines from high-redshift astrophysical objects.

astro-ph↗
arXiv2001

Spatially Anisotropic Four-Dimensional Gauge Interactions, Planar Fermions and Magnetic Catalysis

We consider magnetic catalysis in a field-theoretic system of (3+1)-dimensional Dirac fermions with anisotropic kinetic term. By placing the system in a strong external magnetic field, we examine magnetically-induced fermion mass generation. When the coupling anisotropy is strong, in which case the fermions effectively localize on the plane, we find a significant enhancement of the induced mass gap compared to the isotropic four-dimensional case of quantum electrodynamics. As expected on purely dimensional grounds, the mass and critical temperature scale with the square root of the magnetic field. This phenomenon might be related to recent experimental findings on magnetically-induced gaps at the nodes of d-wave superconducting gaps in high-temperature cuprates.

hep-ph↗
arXiv2001

Cosmological Evolution in a Type-0 String Theory

We study the cosmological evolution of a type-0 string theory by employing non-criticality, which may be induced by fluctuations of the D3 brane worlds. We check the consistency of the approach to O(alpha ') in the corresponding sigma-model. The ten-dimensional theory is reduced to an effective four-dimensional model, with only time dependent fields. We show that the four-dimensional universe has an inflationary phase and graceful exit from it, while the other extra dimensions are stabilized to a constant value, with the fifth dimension much larger than the others. We pay particular attention to demonstrating the role of tachyonic matter in inducing these features. The Universe asymptotes, for large times, to a non-accelerating linearly-expanding Universe with a time-dependent dilaton and a relaxing to zero vacuum energy a la quintessence.

hep-th↗
arXiv2001

\$tring Theory and an Accelerating Universe

An accelerating Universe can be accommodated naturally within non-critical string theory, in which scattering is described by a superscattering matrix \$ that does not factorize as a product of $S$- and $S^\dagger$-matrix elements and time evolution is described by a modified Liouville equation characteristic of open quantum-mechanical systems. We describe briefly alternative representations in terms of the stochastic Ito and Fokker-Planck equations. The link between the vacuum energy and the departure from criticality is stressed. We give an explicit example in which non-marginal \$tring couplings cause a departure from criticality, and the corresponding cosmological vacuum energy relaxes to zero à la quintessence.

hep-th↗
arXiv2000

Space-Time Foam Effects on Particle Interactions and the GZK Cutoff

Modelling space-time foam using a non-critical Liouville-string model for the quantum fluctuations of D branes with recoil, we discuss the issues of momentum and energy conservation in particle propagation and interactions. We argue that momentum should be conserved exactly during propagation and on the average during interactions, but that energy is conserved only on the average during propagation and is in general not conserved during particle interactions, because of changes in the background metric. We discuss the possible modification of the GZK cutoff on high-energy cosmic rays, in the light of this energy non-conservation as well as the possible modification of the usual relativistic momentum-energy relation.

hep-th↗