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Matter-Antimatter Asymmetry in the Universe via String-Inspired CPT Violation at Early ErasAug 28 2017In four-space-time dimensional string/brane theory, obtained either through compactification of the extra spatial dimensions, or by appropriate restriction to brane worlds with three large spatial dimensions, the rich physics potential associated with ... More

Supersymmetry, Cosmological Constant and Inflation: Towards a fundamental cosmic picture via "running vacuum"Dec 19 2015On the occasion of a century from the proposal of General relativity by Einstein, I attempt to tackle some open issues in modern cosmology, via a toy but non-trivial model. Specifically, I would like to link together: (i) the smallness of the cosmological ... More

Spontaneous CPT Violation and Quantum Anomalies in a Model for Matter-Antimatter Asymmetry in the CosmosDec 03 2018We review scenarios of baryogenesis through leptogenesis at early epochs of the universe, in string-inspired minimal extensions of the Standard Model (SM), involving heavy right-handed Majorana neutrinos. Spontaneous violation of CPT symmetry is induced ... More

Regularised Kalb-Ramond Magnetic Monopole with Finite EnergyApr 05 2018May 29 2018In a previous work we suggested a self-gravitating electromagnetic monopole solution in a string-inspired model involving global spontaneous breaking of a $SO(3)$ internal symmetry and Kalb-Ramond (KR) axions, stemming from an antisymmetric tensor field ... More

Inflation via Gravitino Condensation in Dynamically Broken SupergravitySep 10 2014Gravitino-condensate-induced inflation via the super-Higgs effect is a UV-motivated scenario for both inflating the early universe and breaking local supersymmetry dynamically, entirely independent of any coupling to external matter. As an added benefit, ... More

The role of temperature dependent string-inspired CPT violating backgrounds in leptogenesis and the chiral magnetic effectOct 31 2018In a temperature dependent CPT-Violating (CPTV) axial time-like background (induced by the Kalb-Ramond tensor field of string theory) we discuss leptogenesis by solving the Boltzmann equation.The current work non-trivially modifies the framework of a ... More

Quantum Anomalies, Running Vacuum and Leptogenesis: an InterplayMay 14 2019We discuss a connection between gravitational-wave physics, quantum theory anomalies, right-handed (sterile) neutrinos, (spontaneous) CPT Violation and Leptogenesis, within the framework of string-inspired cosmological models. In particular, we present ... More

Environmental CPT Violation in an Expanding Universe in String TheoryApr 19 2013Dec 17 2013We consider a model of an expanding Universe in string theory that yields `environmental' CPT violation for fermions, in the sense of different dispersion relations for fermions and antifermions. These are induced by a cosmological background with constant ... More

The signal of ill-defined CPT weakening entanglement in the $B_d$ systemDec 16 2016In the presence of quantum gravity fluctuations (space-time foam), the CPT operator may be ill-defined. Its perturbative treatment leads to a modification of the Einstein-Podolsky-Rosen correlation of the neutral meson system by adding an Entanglement-weakening ... More

Complete Normal Ordering 1: FoundationsDec 08 2015Jul 19 2016We introduce a new prescription for quantising scalar field theories perturbatively around a true minimum of the full quantum effective action, which is to `complete normal order' the bare action of interest. When the true vacuum of the theory is located ... More

Physics reach of MoEDAL at LHC: magnetic monopoles, supersymmetry and beyondDec 21 2016MoEDAL is a pioneering experiment designed to search for highly ionising messengers of new physics such as magnetic monopoles or massive (pseudo-)stable charged particles, that are predicted to exist in a plethora of models beyond the Standard Model. ... More

Decoherent Neutrino Mixing, Dark Energy and Matter-Antimatter AsymmetryJun 03 2004Nov 02 2004A CPT violating decoherence scenario can easily account for all the experimental evidence in the neutrino sector including LSND. In this work it is argued that this framework can also accommodate the Dark Energy content of the Universe, as well as the ... More

Confronting MOND and TeVeS with strong gravitational lensing over galactic scales: an extended surveyMay 22 2012Nov 11 2012The validity of MOND and TeVeS models of modified gravity has been recently tested by using lensing techniques, with the conclusion that a non-trivial component in the form of dark matter is needed in order to match the observations. In this work those ... More

Some Aspects of String Cosmology and the LHCSep 30 2012Oct 10 2012I discuss some (unconventional) aspects of String Cosmology of relevance to supersymmetric dark matter searches at the Large Hadron Collider (LHC) at CERN. In particular, I analyse the role of time-dependent dilaton fields in relaxing some of the stringent ... More

Neutrinos and the UniverseOct 17 2011In this talk, I review the potential connection of neutrinos to the Physics of the Early Universe, in particular the r\^ole of (sterile) neutrinos to leptogenesis/baryogenesis and the dark sector of the Universe. The possibility of CPT Violation among ... More

The issue of Dark Energy in String TheoryJul 01 2006Recent astrophysical observations, pertaining to either high-redshift supernovae or cosmic microwave background temperature fluctuations, as those measured recently by the WMAP satellite, provide us with data of unprecedented accuracy, pointing towards ... More

CPT Violation: What and where to look forJun 28 2005In this review I classify the possible ways of CPT violation, and I describe briefly their phenomenology, in both terrestrial and astrophysical experiments, including antimatter factories, neutral mesons and neutrinos, and discuss the various sensitivities. ... More

Probing Lorentz Violating (Stringy) Quantum Space-Time FoamSep 12 2009Quantum Space Time may be characterized by a plethora of novel phenomena, such as Lorentz violations and non-trivial refractive indices, stochastic metric fluctuation effects leading to decoherence of quantum matter and non-commutativity of space-time ... More

Decoherence and CPT Violation in a Stringy Model of Space-Time FoamJun 15 2009I discuss a model inspired from the string/brane framework, in which our Universe is represented as a three brane, propagating in a bulk space time punctured by D0-brane (D-particle) defects. As the D3-brane world moves in the bulk, the D-particles cross ... More

Pseudoscalar Fields in Torsionful Geometries of the Early Universe, the Baryon Asymmetry and Majorana Neutrino Mass GenerationMar 30 2014We discuss here a specific field-theory model, inspired from string theory, in which the generation of a matter-antimatter asymmetry in the Cosmos is due to the propagation of fermions in a non-trivial, spherically asymmetric (and hence Lorentz violating) ... More

Theoretical and Phenomenological Aspects of CPT ViolationMay 20 2003I review briefly various models and ways of Quantum-Gravity induced CPT violation, and discuss in some detail their phenomenology, in particular precision CPT tests in neutral mesons, and hydrogen/antihydrogen spectroscopy. As I shall argue, severe constraints ... More

String CosmologyNov 29 2001`Old' String Theory is a theory of one-dimensional extended objects, whose vibrations correspond to excitations of various target-space field modes including gravity. In these lectures I will give an introduction to low-energy Effective Target-Space Actions ... More

Testing A (Stringy) Model of Quantum GravitySep 13 2000I discuss a specific model of space-time foam, inspired by the modern non-perturbative approach to string theory (D-branes). The model views our world as a three brane, intersecting with D-particles that represent stringy quantum gravity effects, which ... More

Quantum Mechanical Aspects of Cell Microtubules: Science Fiction or Realistic Possibility?Nov 29 2010Recent experimental research with marine algae points towards quantum entanglement at ambient temperature, with correlations between essential biological units separated by distances as long as 20 Angstr\"oms. The associated decoherence times, due to ... More

Stringy Space-Time Foam and High-Energy Cosmic PhotonsOct 26 2010In this review, I discuss briefly stringent tests of Lorentz-violating quantum space-time foam models inspired from String/Brane theories, provided by studies of high energy Photons from intense celestial sources, such as Active Galactic Nuclei or Gamma ... More

Recent Results from Indirect and Direct Dark Matter Searches: Theoretical ScenariosNov 07 2011In this review, I discuss briefly theoretical scenarios concerning the interpretation of recent results from indirect and direct dark matter searches, with emphasis on the former.

Quantum Gravity, Flavour Vacua and SupersymmetryJun 21 2011I review a novel and non-perturbative way of breaking Supersymmetry in the flavour sector of electrically neutral particles, as a result of flavour mixing in the presence of stringy quantum gravity space-time foam backgrounds that violate Lorentz and ... More

CPT Violation and Decoherence in Quantum GravityApr 03 2009In this brief review I discuss ways and tests of CPT-Violation in the context of quantum gravity theories with space-time foam vacua, which entail quantum decoherence of matter propagating in such backgrounds. I cover a wide variety of sensitive probes, ... More

Novel Scenarios for Majorana Neutrino Mass Generation and Leptogenesis from Kalb-Ramond TorsionOct 08 2015The Kalb-Ramond (KR) antisymmetric tensor field arises naturally in the gravitational multiplet of string theory. Nevertheless, the respective low-energy field theory action, in which, for reasons of gauge invariance, the only dependence on the KR field ... More

Some Novel Ways for Neutrino Mass GenerationJun 04 2015I discuss dynamical generation of neutrino masses in unconventional scenarios where the background space-time geometry plays a crucial role. I discuss two types of backgrounds: (i) Lorentz Violating and (ii) Geometries with Torsion. In the former case, ... More

String Quantum Gravity, Lorentz-Invariance Violation and Gamma-Ray AstronomyOct 26 2010In the first part of the review, I discuss ways of obtaining Lorentz-Invariance-Violating (LIV) space-time foam in the modern context of string theory, involving brane world scenarios. The foamy structures are provided by lower-dimensional background ... More

CPT and Quantum Mechanics Tests with Kaons: TheoryJul 28 2006In this talk I review theoretical motivations for possible CPT Violation and deviations from ordinary quantum mechanical behavior of field theoretic systems in some quantum gravity models, and I describe the relevant precision tests using neutral and ... More

CPT Violation: Theory and PhenomenologyApr 17 2005Invariance under the combined transformations of CPT (in any order) is guaranteed in Quantum Field Theory in flat space times due to a basic theorem (CPT Theorem). The currently used formalism of particle physics phenomenology is based on this theorem. ... More

Quantum Gravity, Cosmology, (Liouville) Strings and Lorentz InvarianceOct 08 2002Oct 11 2002I review some aspects of non-critical strings in connection with Lorentz-Invariance violating approaches to quantum gravity. I also argue how non-critical strings may provide a unifying framework where string Cosmology and quantum gravity may be tackled ... More

Gravitino Condensates in the Early Universe and InflationDec 19 2014We review work on the formation of gravitino condensates via the super-Higgs effect in the early Universe. This is a scenario for both inflating the early universe and breaking local supersymmetry (supergravity), entirely independent of any coupling to ... More

Theory Overview of Testing Fundamental SymmetriesDec 16 2013I review first some theoretical motivations for violation of Lorentz and/or CPT Invariance. Although the latter symmetries may be violated in a quantum gravity setting, nevertheless there are situations in which these violations are due to a given classical ... More

Quantum Gravity, CPT symmetry and Entangled StatesNov 09 2008There may unique ("smoking-gun") signatures of the breakdown of CPT symmetry, induced in some models of Quantum Gravity entailing decoherence for quantum matter. Such effects can be observed in entangled states of neutral mesons via modifications of the ... More

Quantum-Gravity Induced Lorentz Violation and Dynamical Mass GenerationNov 15 2010In Ref. [1] (by J. Alexandre) a minimal extension of (3+1)-dimensional Quantum Electrodynamics has been proposed, which includes Lorentz-Violation (LV) in the form of higher-(spatial)-derivative isotropic terms in the gauge sector, suppressed by a mass ... More

High-Energy gamma-ray Astronomy and String TheoryMar 02 2009There have been observations, first from the MAGIC Telescope (July 2005) and quite recently (September 2008) from the FERMI Satellite Telescope, on non-simultaneous arrival of high-energy photons from distant celestial sources. In each case, the highest ... More

Logarithmic Conformal Field Theories and Strings in Changing BackgroundsJul 05 2004I review a particular class of physical applications of Logarithmic Conformal Field Theory in strings propagating in changing (not necessarily conformal) backgrounds, namely D-brane recoil in flat or time-dependent cosmological backgrounds. The role of ... More

On CPT Symmetry: Cosmological, Quantum-Gravitational and other possible violations and their phenomenologySep 18 2003I discuss various ways in which CPT symmetry may be violated, and their phenomenology in current or immediate future experimental facilities, both terrestrial and astrophysical. Specifically, I discuss first violations of CPT symmetry due to the impossibility ... More

On the Thermodynamics of a Gas of AdS Black Holes and the Quark-Hadron Phase TransitionFeb 25 1999We discuss the thermodynamics of a gas of black holes in five-dimensional anti-de-Sitter (AdS) space, showing that they are described by a van der Waals equation of state. Motivated by the Maldacena conjecture, we relate the energy density and pressure ... More

A proposal on the possibility of detecting D-particlesApr 23 2001In a previous study we showed that D0-branes (particles) can operate as sources of very-high-energy radiation, as a result of an unstable spacetime distortion that follows a D0-particle/closed string state scattering. The effect can happen only if the ... More

A study of spacetime distortion around a scattered recoiling D-particle and possible astrophysical consequencesMar 15 2001We study a four-dimensional spacetime induced by the recoil of a D(irichlet)-particle, embeded in it, due to scattering by a moving string. The induced spacetime has curvature only up to a radius that depends on the energy of the incident string. Outside ... More

Infinitely Coloured Black HolesSep 03 1999We formulate the field equations for $SU(\infty)$ Einstein-Yang-Mills theory, and find spherically symmetric black-hole solutions. This model may be motivated by string theory considerations, given the enormous gauge symmetries which characterize string ... More

Mass Hierarchies in Lorentz-Violation-induced Dynamical Mass ModelsApr 08 2011We discuss the issue of fermion mass hierarchies between lepton and quark families in toy models of dynamical generation of fermion masses through minimal Lorentz Invariance Violation. Realistic hierarchies in chiral theories necessitate an extended gauge ... More

Anomalous Majorana Neutrino Masses from Torsionful Quantum GravitySep 27 2012Dec 08 2012The effect of quantum torsion in theories of quantum gravity is usually described by an axion-like field which couples to matter and to gravitation and radiation gauge fields. In perturbation theory, the couplings of this torsion-descent axion field are ... More

String cosmology from a novel renormalization perspectiveSep 14 2005Mar 06 2007We study small perturbations around the exactly marginal time-dependent string configuration of [1], and demonstrate the lack of the appropriate linearization. This implies that this configuration is an isolated fixed point of the $\alpha^{'}$ flow in ... More

Magnetic Monopoles from Global Monopoles in the presence of Kalb-Ramond TorsionJul 05 2016Nov 22 2016Possible classical solutions for electromagnetic monopoles induced by gravitational (global) monopoles in the presence of torsion are found. Such solutions rely on a non-zero (Kalb-Ramond) torsion strength, which may characterise low energy theories inspired ... More

Singular lensing from the scattering on special space-time defectsDec 09 2017It is well known that certain special classes of self-gravitating point-like defects, such as global (non gauged) monopoles, give rise to non-asymptotically flat space-times characterized by solid angle deficits, whose size depends on the details of the ... More

Aspects of Duality in Nodal LiquidsOct 10 2002Starting from a microscopic t-J like model and a SU(2) spin-charge separation ansatz, a relativistic continuum gauge lagrangian is obtained in the vicinity of a nodal point of the Fermi surface. The excitations in the pseudogap phase are described by ... More

Vacuum Energy and Cosmological Supersymmetry Breaking in Brane WorldsMay 29 2002Sep 29 2002In the context of a toy model we discuss the phenomenon of colliding five-branes, with two of the extra space dimensions compactified on tori. In one of the branes (hidden world) the torus is magnetised. Assuming opposite-tension branes, we argue that ... More

Impulse Action on D-particles in Robertson-Walker Space Times, Higher-Order Logarithmic Conformal Algebras and Cosmological HorizonsJun 16 2001We demonstrate that an impulse action (`recoil') on a D-particle embedded in a (four-dimensional) cosmological Robertson-Walker (RW) spacetime is described, in a $\sigma$-model framework, by a suitably extended higher-order logarithmic world-sheet algebra ... More

On the Interpretation of Gravitational Corrections to Gauge CouplingsDec 20 2010Several recent papers discuss gravitational corrections to gauge couplings that depend quadratically on the energy. In the framework of the background-field approach, these correspond in general to adding to the effective action terms quadratic in the ... More

Non-extensive statistics in stringy space-time foam models and entangled meson statesDec 20 2008Mar 20 2009The possibility of generation of non-extensive statistics, in the sense of Tsallis, due to space-time foam is discussed within the context of a particular kind of foam in string/brane-theory, the D-particle foam model . The latter involves point-like ... More

A Lorentz-Violating Alternative to Higgs Mechanism?Aug 19 2011We consider a four-dimensional field-theory model with two massless fermions, coupled to an Abelian vector field without flavour mixing, and to another Abelian vector field with flavour mixing. Both Abelian vectors have a Lorentz-violating kinetic term, ... More

Inflation induced by Gravitino Condensation in SupergravityAug 08 2013Oct 08 2013We discuss the emergence of an inflationary phase in supergravity with the super-Higgs effect due to dynamical spontaneous breaking of supersymmetry, in which the role of the inflaton is played by the gravitino condensate. Realistic models compatible ... More

An Alternative to Exact Renormalization and Cosmological Solutions in String TheoryAug 10 2005Feb 14 2007In this work we review the application of a functional method, serving as an alternative to the Wilsonian Exact Renormalization approach, to stringy bosonic $\sigma$-models with metric and dilaton backgrounds on a spherical world sheet [1]. We derive ... More

Exact Solutions and the Cosmological Constant Problem in Dilatonic-Domain-Wall Higher-Curvature String GravityMay 29 2002In this article we extend previous work by the authors, and elaborate further on the structure of the general solution to the graviton and dilaton equations of motion in brane world scenaria, in the context of five-dimensional effective actions with O(\alpha ... More

Putting Liouville String Models of (Quantum) Gravity to TestAug 01 2001Aug 02 2001Critical String Theory is by definition an $S$-matrix theory. In this sense, (quantum) gravity situations where a unitary $S$-matrix may not be a well-defined concept, as a consequence of the existence of macroscopic (global) or microscopic (local) gravitational ... More

Nodal Liquids and DualityJun 14 2000Jul 18 2000Using a SU(2)x U(1) gauge theory for a t-J model around a node of the Fermi surface, we discuss patterns of dynamical symmetry breaking, which may lead to a pseudogap phase and to the appearance of narrow one-dimensional spatial structures, induced by ... More

Probes of Lorentz ViolationNov 04 2011Lorentz invariance is such an important principle of fundamental physics that it should constantly be subjected to experimental scrutiny as well as theoretical questioning. Distant astrophysical sources of energetic photons with rapid time variations, ... More

Finite-energy dressed string-inspired Dirac-like monopolesDec 03 2018On extending the Standard Model (SM) Lagrangian, through a non-linear Born-Infeld (BI) hypercharge term with a parameter $\beta$ (of dimensions of [mass]$^2$), a finite energy monopole solution was claimed by Arunasalam and Kobakhidze [1]. We report on ... More

Magnetic Monopoles from Global Monopoles in the presence of Kalb-Ramond TorsionJul 05 2016Possible classical solutions for electromagnetic monopoles induced by gravitational (global) monopoles in the presence of torsion are found. Such solutions rely on a non-zero (Kalb-Ramond) torsion strength, which may characterise low energy theories inspired ... More

String-Inspired Higher-Curvature Terms and the Randall-Sundrum ScenarioAug 08 2000Aug 13 2000We consider the O(a') string effective action, with Gauss-Bonnet curvature-squared and fourth-order dilaton-derivative terms, which is derived by a matching procedure with string amplitudes in five space-time dimensions. We show that a non-factorizable ... More

Comments on Extended t-J Models, Nodal Liquids and SupersymmetrySep 21 1999Sep 22 1999In the context of extended t-J models, with intersite Coulomb interactions, nodal liquids are discussed. We use the spin-charge separation ansatz as applied to the nodes of a d-wave superconducting gap. Such a situation may be of relevance to the physics ... More

On the Role of Space-Time Foam in Breaking Supersymmetry via the Barbero-Immirzi ParameterAug 03 2011Nov 01 2011We discuss how: (i) a dilaton/axion superfield can play the role of a Barbero-Immirzi field in four-dimensional conformal quantum supergravity theories, (ii) a fermionic component of such a dilaton/axion superfield may play the role of a Goldstino in ... More

Induced Curvature in Brane Worlds by Surface Terms in String Effective Actions with Higher-Curvature CorrectionsMar 31 2005Dec 22 2005In string-inspired effective actions, representing the low-energy bulk dynamics of brane/string theories, the higher-curvature ghost-free Gauss-Bonnet combination is obtained by local field redefinitions which leave the (perturbative) string amplitudes ... More

CPT-Violating Leptogenesis induced by Gravitational DefectsNov 05 2012We explore leptogenesis induced by the propagation of neutrinos in gravitational backgrounds that may occur in string theory. The first background is due to linear dilatons and the associated Kalb-Ramond field (axion) in four non-compact space-time dimensions ... More

Magnetic Monopoles from Global Monopoles in the presence of Kalb-Ramond TorsionJul 05 2016Feb 27 2017Possible classical solutions for electromagnetic monopoles induced by gravitational (global) monopoles in the presence of torsion are found. Such solutions rely on a non-zero (Kalb-Ramond) torsion strength, which may characterise low energy theories inspired ... More

Neutrinos in the Early Universe, Kalb-Ramond Torsion and Matter-Antimatter AsymmetryDec 18 2013The generation of a matter-antimatter asymmetry in the Universe may be induced by the propagation of fermions in non-trivial, spherically asymmetric (and hence Lorentz violating) gravitational backgrounds. Such backgrounds may characterise the epoch of ... More

Towards a microscopic construction of flavour vacua from a space-time foam modelOct 24 2007The effect on flavour oscillations of simple expanding background space-times, motivated by some D-particle foam models, is calculated for a toy-model of bosons with flavour degrees of freedom. The presence of D-particle defects in the space-time, which ... More

A novel non-perturbative approach to String CosmologyDec 01 2005Jun 24 2006We develop an exact functional method applied to the bosonic string on a shperical world sheet, in graviton and dilaton backgrounds, consistent with conformal invariance. In this method, quantum fluctuations are controled by the amplitude of the kinetic ... More

A Possible Quantum-Gravitational Origin of the Neutrino Mass Difference ?Apr 09 2006We discuss the theoretical possibility that the neutrino mass differences have part of their origin in the quantum-decoherence-inducing medium of space-time foam, which characterises some models of quantum gravity, in much the same way as the celebrated ... More

Radiatively-induced Magnetic moment in four-dimensional anisotropic QED in an external magnetic fieldNov 23 2001We discuss one-loop radiatively-induced magnetic moment in four-dimensional quantum electrodynamics (QED) with anisotropic coupling, and examine various cases which may be of interest in effective gauge theories of antiferromagnets, whose planar limit ... More

D-particle Recoil Space Times and "Glueball" MassesJun 02 2000Jun 03 2000We discuss the properties of matter in a D-dimensional anti-de-Sitter-type space time induced dynamically by the recoil of a very heavy D(irichlet)-particle defect embedded in it. The particular form of the recoil geometry, which from a world-sheet view ... More

Nodal Liquids in Extended t-J Models and Dynamical SupersymmetryDec 17 1999In the context of extended t-J models, with intersite Coulomb interactions of the form $-V\sum\limits_{< {i,j} >} {n_in_j}$, with n_i denoting the electron number operator at site i, nodal liquids are discussed. We use the spin-charge separation ansatz ... More

Starobinsky-type Inflation in Dynamical Supergravity Breaking ScenariosDec 18 2013In the context of dynamical breaking of local supersymmetry (supergravity), including the Deser-Zumino super-Higgs effect, for the simple but quite representative cases of N=1, D=4 supergravity, we discuss the emergence of Starobinsky-type inflation, ... More

Dynamical Supergravity Breaking via the Super-Higgs Effect RevisitedOct 15 2013We investigate the dynamical breaking of local supersymmetry (supergravity), including the Deser-Zumino super-Higgs effect, via the corresponding one-loop effective potential for the simple but quite representative cases of N=1, D=4 simple supergravity ... More

Dynamical generation of field mixing via flavor vacuum condensateJul 19 2018Feb 28 2019In this paper we study dynamical chiral symmetry breaking of a generic quantum field theoretical model with global chiral flavor symmetry. By purely algebraic means we analyze the vacuum structure for different symmetry breaking schemes and show explicitly ... More

Composite Supersymmetries in low-dimensional systemsFeb 07 2002Starting from a N=1 scalar supermultiplet in 2+1 dimensions, we demonstrate explicitly the appearance of induced N=1 vector and scalar supermultiplets of composite operators made out of the fundamental supersymmetric constituents. We discuss an extension ... More

Non-linear Schroedinger Dynamics of Matrix D-branesSep 19 1999May 30 2000We formulate an effective Schroedinger wave equation describing the quantum dynamics of a system of D0-branes by applying the Wilson renormalization group equation to the worldsheet partition function of a deformed sigma-model describing the system, which ... More

Light-by-Light Scattering Constraint on Born-Infeld TheoryMar 24 2017May 24 2017The recent measurement by ATLAS of light-by-light scattering in LHC Pb-Pb collisions is the first direct evidence for this basic process. We find that it requires the mass scale of a nonlinear Born-Infeld extension of QED to be $\gtrsim 100$~GeV, a much ... More

The Price of an Electroweak MonopoleFeb 04 2016Feb 10 2016In a recent paper, Cho, Kim and Yoon (CKY) have proposed a version of the SU(2) $\times$ U(1) Standard Model with finite-energy monopole and dyon solutions. The CKY model postulates that the effective U(1) gauge coupling $\to \infty$ very rapidly as the ... More

Wess-Zumino Inflation in Light of PlanckMar 25 2013We discuss cosmological inflation in the minimal Wess-Zumino model with a single massive chiral supermultiplet. With suitable parameters and assuming a plausible initial condition at the start of the inflationary epoch, the model can yield scalar perturbations ... More

World-Sheet Logarithmic Operators and Target Space Symmetries in String TheoryDec 28 1995Jan 11 1996We discuss the target-space interpretation of the world-sheet logarithmic operators in string theory. These operators generate the normalizable zero modes (discrete states) in target space, which restore the symmetries of the theory broken by the background. ... More

Matrix D-brane Dynamics, Logarithmic Operators and Quantization of Noncommutative SpacetimeAug 20 1998We describe the structure of the moduli space of $\sigma$-model couplings for the worldsheet description of a system of $N$ D-particles, in the case that the couplings are represented by a pair of logarithmic recoil operators. We derive expressions for ... More

Gradient Flow in Logarithmic Conformal Field TheoryMar 11 1998Apr 16 1998We establish conditions under which the worldsheet beta-functions of logarithmic conformal field theories can be derived as the gradient of some scalar function on the moduli space of running coupling constants. We derive a renormalization group invariant ... More

On the Possibility of Superluminal Neutrino PropagationSep 28 2011Nov 22 2011We analyze the possibility of superluminal neutrino propagation delta v = (v - c)/c > 0 as indicated by OPERA data, in view of previous phenomenological constraints from supernova SN1987a and gravitational Cerenkov radiation. We argue that the SN1987a ... More

Condensate Structure of D-particle Induced Flavour VacuumJan 14 2012It is argued that four Fermi interactions induced by non-perturbative effects due to scattering of stringy matter from D-particles, D-instantons and more generally bulk gauge fields in models with large extra dimensions have in specific situations condensate ... More

Flavour Condensates in Brane Models and Dark EnergyJul 29 2009In the context of a microscopic model of string-inspired foam, in which foamy structures are provided by brany point-like defects (D-particles) in space-time, we discuss flavour mixing as a result of flavour non-preserving interactions of (low-energy) ... More

Graviton propagation within the context of the D-material universeMay 09 2016Motivated by the recent breakthrough of the detection of Gravitational Waves (GW) from coalescent black holes by the aLIGO interferometers, we study the propagation of GW in the {\sl D-material universe}, which we have recently shown to be compatible ... More

The MAGIC of SSC and how it affects LHCFeb 09 2009We discuss the phenomenology of Supercritical String Cosmology (SSC) in the context of Dark Matter constraints on supersymmetric particle physics models at LHC. We also link our results with recent findings of the MAGIC, H.E.S.S. and Fermi Telescopes ... More

Antisymmetric-Tensor and Electromagnetic effects in an alpha'-non-perturbative Four-Dimensional String CosmologyAug 08 2007Starting from an exact (in the Regge slope alpha') functional method for a bosonic stringy sigma-model, we investigate four-dimensional cosmological string solutions in graviton, dilaton and antisymmetric tensor backgrounds, compatible with world-sheet ... More

Leptogenesis from Heavy Right-Handed Neutrinos in CPT Violating BackgroundsDec 08 2017We discuss leptogenesis in a model with heavy right-handed Majorana neutrinos propagating in a constant but otherwise generic CPT-violating axial time-like background (which could be motivated by string theory considerations). At temperatures much higher ... More

Quasi-relativistic fermions and dynamical flavour oscillationsApr 29 2014Aug 09 2014We introduce new Lorentz-symmetry violating kinematics for a four-fermion interaction model, where dynamical mass generation is allowed, irrespectively of the strength of the coupling. In addition, these kinematics lead to a quasi-relativistic dispersion ... More

Starobinsky-like inflation and running vacuum in the context of SupergravityMay 17 2015Jul 21 2016We describe the primeval inflationary phase of the early Universe within a quantum field theoretical (QFT) framework that can be viewed as the effective action of vacuum decay in the early times. Interestingly enough, the model accounts for the "graceful ... More

Do we Come from a Quantum Anomaly?May 12 2019We present a string-based picture of the cosmological evolution in which (CP-violating) gravitational anomalies acting during the inflationary phase of the universe cause the vacuum energy density to "run" with the effective Hubble parameter squared, ... More

Non-perturbative time-dependent String Backgrounds and Axion-induced Optical ActivityApr 15 2008Conformal invariance for bosonic strings in time-dependent backgrounds of graviton, dilaton and Kalb-Ramond field is obtained by imposing Weyl-beta functions to be homogeneous in time, to all orders in $\alpha^{'}$. This construction is possible in any ... More

Stringy Space-Time Foam, Finsler-like Metrics and Dark Matter RelicsSep 15 2010We discuss modifications of the thermal Dark Matter (DM) relic abundances in stringy cosmologies with D-particle space-time foamy backgrounds. As a result of back-reaction of massive DM on the background space-time, owing to its interaction with D-particle ... More