Dent, T., Leontaris, G. K., Psallidas, A., Rizos, J.
We discuss renormalization effects on neutrino masses and mixing angles in a supersymmetric string-inspired SU(4) X SU(2)_L X SU(2)_R X U(1)_X model, with matter in fundamental and antisymmetric...
A D-brane inspired U(3)_CxU(3)_LxU(3)_R model (2005)
Motivated by D-brane scenarios, we consider a non-supersymmetric model based on the gauge symmetry U(3)_CxU(3)_LxU(3)_R$ which is equivalent to the SU(3)^3 ``trinification'' model supplemented by...
D-branes and the Standard Model (2005)
Antoniadis, I., Kiritsis, E., Rizos, J., Tomaras, T. N.
We perform a systematic study of the Standard Model embedding in a D-brane configuration of type I string theory at the TeV scale. We end up with an attractive model and we study several...
Anomalous U(1)s in Type I superstring vacua (2005)
Antoniadis, I., Kiritsis, E., Rizos, J.
We perform a systematic string computation of the masses of anomalous U(1) gauge bosons in four-dimensional orientifold vacua, and we study their localization properties in the internal...
Gauge coupling and fermion mass relations in low string scale brane models (2005)
Gioutsos, D. V., Leontaris, G. K., Rizos, J.
We analyze the gauge coupling evolution in brane inspired models with $U(3) \times U(2) \times U(1)^N$ symmetry at the string scale. We restrict to the case of brane configurations with two and three...
Majorana Neutrino Masses from Anomalous U(1) Symmetries (2004)
Leontaris, G. K., Rizos, J., Psallidas, A.
We explore the possibility of interpreting the solar and atmospheric neutrino data within the context of the Minimal Supersymmetric Standard Model augmented by a single U(1) anomalous family symmetry...
Classification of the chiral Z2XZ2 fermionic models in the heterotic superstring (2004)
Faraggi, A. E., Kounnas, C., Nooij, S. E. M., Rizos, J.
The first particle physics observable whose origin may be sought in string theory is the triple replication of the matter generations. The class of Z2XZ2 orbifolds of six dimensional compactified...
Towards the classification of Z2XZ2 fermionic models (2003)
Faraggi, A. E., Kounnas, C., Nooij, S. E. M., Rizos, J.
We develop a formalism that allows a complete classification of four-dimensional Z2XZ2 heterotic string models. Three generation models in a sub-class of these compactifications are related to the...
D-branes and the Standard Model (2003)
Antoniadis, I., Kiritsis, E., Rizos, J., Tomaras, T. N.
We perform a systematic study of the Standard Model embedding in a D-brane configuration of type I string theory at the TeV scale. We end up with an attractive model and we study several...
D-branes and the Standard Model (2003)
Antoniadis, I., Kiritsis, E., Rizos, J., Tomaras, T. N.
We perform a systematic study of the Standard Model embedding in a D-brane configuration of type I string theory at the TeV scale. We end up with an attractive model and we study several...
D-branes and the Standard Model (2002)
Antoniadis, Ignatios, Kiritsis, Elias B, Rizos, J, Tomaras, T N
We perform a systematic study of the Standard Model embedding in a D-brane configuration of type I string theory at the TeV scale. We end up with an attractive model and we study several...
D-branes and the Standard Model (2002)
Antoniadis, I., Kiritsis, E., Rizos, J., Tomaras, T. N.
We perform a systematic study of the Standard Model embedding in a D-brane configuration of type I string theory at the TeV scale. We end up with an attractive model and we study several...
Five-Brane Configurations without a Strong Coupling Regime (2002)
Kiritsis, E., Kounnas, C., Petropoulos, P. M., Rizos, J.
Five-brane distributions with no strong coupling problems and high symmetry are studied. The simplest configuration corresponds to a spherical shell of branes with S^3 geometry and symmetry. The...
Anomalous U(1)s in Type I superstring vacua (2002)
Antoniadis, Ignatios, Kiritsis, Elias B, Rizos, J
We perform a systematic string computation of the masses of anomalous U(1) gauge bosons in four-dimensional orientifold vacua, and we study their localization properties in the internal...
Anomalous U(1)s in Type I superstring vacua (2002)
Antoniadis, I., Kiritsis, E., Rizos, J.
We perform a systematic string computation of the masses of anomalous U(1) gauge bosons in four-dimensional orientifold vacua, and we study their localization properties in the internal...
Non-factorisable metrics and Gauss--Bonnet terms in higher dimensions (2002)
Abdesselam, B., Chakrabarti, A., Rizos, J., Tchrakian, D. H.
An iterative construction of higher order Einstein tensors for a maximally Gauss-Bonnet extended gravitational Lagrangian was introduced in a previous paper. Here the formalism is extended to...
Anomalous U(1)s in Type I superstring vacua (2002)
Antoniadis, I., Kiritsis, E., Rizos, J.
We perform a systematic string computation of the masses of anomalous U(1) gauge bosons in four-dimensional orientifold vacua, and we study their localization properties in the internal...
Anomalous U(1)s in Type I superstring vacua (2002)
Antoniadis, I., Kiritsis, E., Rizos, J.
We perform a systematic string computation of the masses of anomalous U(1) gauge bosons in four-dimensional orientifold vacua, and we study their localization properties in the internal...
A Pati-Salam model from branes (2000)
We explore the possibility of embedding the Pati-Salam model in the context of Type I brane models. We study a generic model with U(4)_C x U(2)_L x U(2)_R gauge symmetry and matter fields compatible...
A Pati-Salam model from branes (2000)
We explore the possibility of embedding the Pati-Salam model in the context of Type I brane models. We study a generic model with U(4)_C x U(2)_L x U(2)_R gauge symmetry and matter fields compatible...
String-Inspired Higher-Curvature Terms and the Randall-Sundrum Scenario (2000)
Mavromatos, Nikolaos E, Rizos, J
We consider the O(a') string effective action, with Gauss-Bonnet curvature-squared and forth-order dilaton-derivative terms, which is derived by a matching procedure with string amplitudes in five...
Implications of Anomalous U(1) Symmetry in Unified Models: the Flipped SU(5) x U(1) Paradigm (2000)
Ellis, Jonathan Richard, Leontaris, George K, Rizos, J
A generic feature of string-derived models is the appearance of an anomalousAbelian U(1)_A symmetry which, among other properties, constrains the Yukawacouplings and distinguishes the three families...
Implications of Anomalous U(1) Symmetry in Unified Models: the Flipped SU(5) x U(1) Paradigm (2000)
Ellis, John, Leontaris, G. K., Rizos, J.
A generic feature of string-derived models is the appearance of an anomalous Abelian U(1)_A symmetry which, among other properties, constrains the Yukawa couplings and distinguishes the three...
In this paper, we present solutions to the fermion mass hierarchy problem in the context of the minimal supersymmetric standard theory augmented by an anomalous family-dependent U(1)_X symmetry. The...
In this paper, we present solutions to the fermion mass hierarchy problem in the context of the minimal supersymmetric standard theory augmented by an anomalous family-dependent U(1)_X symmetry. The...
Higgs Mass Textures in Flipped SU(5) (1999)
Ellis, Jonathan Richard, Leontaris, George K, Rizos, J
We analyze the Higgs doublet-triplet mass splitting problem in the version of flipped SU(5) derived from string theory. Analyzing non-renormalizable terms up to tenth order in the superpotential, we...
Higgs Mass Textures in Flipped SU(5) (1999)
Ellis, John, Leontaris, G. K., Rizos, J.
We analyze the Higgs doublet-triplet mass splitting problem in the version of flipped SU(5) derived from string theory. Analyzing non-renormalizable terms up to tenth order in the superpotential, we...
Gregori, A, Kounnas, Costas, Rizos, J
Using free world-sheet fermions, we construct and classify all the N=2, Z2 X Z2 four-dimensional orbifolds of the type IIA/B strings for which the orbifold projections act symmetrically on the left...
Gregori, A., Kounnas, C., Rizos, J.
Using free world-sheet fermions, we construct and classify all the N=2, Z2 X Z2 four-dimensional orbifolds of the type IIA/B strings for which the orbifold projections act symmetrically on the left...
In the context of the free-fermionic formulation of the heterotic superstring, we construct a three generation N=1 supersymmetric SU(4)xSU(2)LxSU(2)R model supplemented by an SU(8) hidden gauge...
In the context of the free-fermionic formulation of the heterotic superstring, we construct a three generation N=1 supersymmetric SU(4)xSU(2)LxSU(2)R model supplemented by an SU(8) hidden gauge...
String Threshold corrections in models with spondaneously broken supersymmetry (1998)
Kiritsis, Elias B, Kounnas, Costas, Petropoulos, P M, Rizos, J
We analyse a class of four-dimensional heterotic ground states with N=2 space-time supersymmetry. From the ten-dimensional perspective, such models can be viewed as compactifications on a...
String Threshold corrections in models with spontaneously broken supersymmetry (1998)
Kiritsis, E., Kounnas, C., Petropoulos, P. M., Rizos, J.
We analyse a class of four-dimensional heterotic ground states with N=2 space-time supersymmetry. From the ten-dimensional perspective, such models can be viewed as compactifications on a...
Suppressing dimension-5 operators in general SU(5) models (1998)
Gomez, M. E., Rizos, J., Tamvakis, K.
We discuss dimension-5 operators in supersymmetric models containing extra hypercharge 1/3 color-triplets. We derive a general formula relating dimension-5 operator to the color-triplet mass matrix....
Singularity-free cosmological solutions in quadratic gravity (1998)
Kanti, P., Rizos, J., Tamvakis, K.
We study a general field theory of a scalar field coupled to gravity through a quadratic Gauss-Bonnet term $\xi(\phi) R^2_{GB}$. The coupling function has the form $\xi(\phi)=\phi^n$, where $n$ is a...
Dilatonic Black Holes in Higher-Curvature String Gravity II: Linear Stability (1997)
Kanti, P., Mavromatos, N. E., Rizos, J., Tamvakis, K., Winstanley, E.
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...
String scale unification in an SU(6)xSU(2) GUT (1997)
We construct and analyze an $SU(6)\times SU(2)$ GUT. The model is k=1 string embedable in the sense that we employ only chiral representations allowed at the k=1 level of the associated Ka\v{c}-Moody...
Dedes, A., Lahanas, A. B., Rizos, J., Tamvakis, K.
We make a complete analysis of radiative symmetry breaking in the MSSM and its $SU(5)$ extensions including low- and high-energy threshold effects in the framework of the two-loop renormalization...
Universality properties of N=2 and N=1 Heterotic threshold corrections (1996)
Kiritsis, Elias B, Kounnas, Costas, Petropoulos, P M, Rizos, J
In the framework of heterotic compactifications, we consider the one-loop corrections to the gauge couplings, which were shown to be free of any infra-red ambiguity. For a class of N=2 models, namely...
Universality properties of N=2 and N=1 Heterotic threshold corrections (1996)
Kiritsis, E., Kounnas, C., Petropoulos, P. M., Rizos, J.
In the framework of heterotic compactifications, we consider the one-loop corrections to the gauge couplings, which were shown to be free of any infra-red ambiguity. For a class of N=2 models, namely...
Solving the decompactification problem in string theory (1996)
Kiritsis, Elias B, Kounnas, Costas, Petropoulos, P M, Rizos, J
We investigate heterotic ground states in four dimensions in which N=4 supersymmetry is spontaneously broken to N=2. N=4 supersymmetry is restored at a decompactification limit corresponding to...
Solving the Decompactification Problem in String Theory (1996)
Kiritsis, E., Kounnas, C., Petropoulos, M., Rizos, J.
We investigate heterotic ground states in four dimensions in which N=4 supersymmetry is spontaneously broken to N=2. N=4 supersymmetry is restored at a decompactification limit corresponding to...
On the heterotic effective action at one-loop, gauge couplings and the gravitational sector (1996)
Kiritsis, Elias B, Kounnas, Costas, Petropoulos, P M, Rizos, J
We present in detail the procedure for calculating the heterotic one-loop effective action. We focus on gravitational and gauge couplings. We show that the two-derivative couplings of the...
On the Heterotic Effective Action at One-Loop, Gauge Couplings and the Gravitational Sector (1996)
Kiritsis, E., Kounnas, C., Petropoulos, M., Rizos, J.
We present in detail the procedure for calculating the heterotic one-loop effective action. We focus on gravitational and gauge couplings. We show that the two-derivative couplings of the...
Universal moduli-dependent thresholds in Z$_{2}$ x Z$_{2}$ orbifolds (1996)
In the context of a recently proposed method for computing exactly string loop corrections regularized in the infra-red, we determine and calculate the universal moduli-dependent part of the...
Universal moduli-dependent thresholds in Z(2)xZ(2) orbifolds (1996)
In the context of a recently proposed method for computing exactly string loop corrections regularized in the infra-red, we determine and calculate the universal moduli-dependent part of the...
Dilatonic black holes in higher curvature string gravity (1995)
Kanti, Panagiota, Mavromatos, Nikolaos E, Rizos, J, Tamvakis, Kyriakos, Winstanley, E
We give analytical arguments and demonstrate numerically the existence of black hole solutions of the 4D Effective Superstring Action in the presence of Gauss-Bonnet quadratic curvature terms. The...
Dilatonic Black Holes in Higher Curvature String Gravity (1995)
Kanti, P., Mavromatos, N. E., Rizos, J., Tamvakis, K., Winstanley, E.
We give analytical arguments and demonstrate numerically the existence of black hole solutions of the $4D$ Effective Superstring Action in the presence of Gauss-Bonnet quadratic curvature terms. The...
On the existence of singularity-free solutions in quartic gravity (1994)
We study a general field theory of a scalar field coupled to gravitation through a quadratic Gauss-Bonnet term $\xi({\phi})$$R_{GB}^2$. We show that, under mild assumptions about the function...
Singularity-free cosmological solutions of the superstring effective action (1993)
Antoniadis, I., Rizos, J., Tamvakis, K.
We study the cosmological solutions of the one loop corrected superstring effective action, in a Friedmann-Robertson-Walker background, and in the presence of the dilaton and modulus fields. A...
Walk-in clinics: implications for family practice.
Rizos, J, Anglin, P, Grava-Gubins, I, Lazar, C
To understand better the reasons for the growth in popularity of walk-in clinics in Canada we surveyed 321 patients with a regular physician in Toronto who attended a walk-in clinic in the same city...
Walk-in clinics: implications for family practice.
Rizos, J, Anglin, P, Grava-Gubins, I, Lazar, C
To understand better the reasons for the growth in popularity of walk-in clinics in Canada we surveyed 321 patients with a regular physician in Toronto who attended a walk-in clinic in the same city...
Keyes, P. D., Tallon, J. M., Rizos, J.
OBJECTIVE: To consider topical anesthetic options available to primary care physicians, indications for their use, and efficacy and safety of these agents as supported by the literature. QUALITY OF...