Nikos Irges - Academia.edu (original) (raw)

Papers by Nikos Irges

Nucl Phys B, 2005

We construct a Z_2 orbifold projection of SU(N) gauge theories formulated in five dimensions with... more We construct a Z_2 orbifold projection of SU(N) gauge theories formulated in five dimensions with a compact fifth dimension. We show through a non-perturbative argument that no boundary mass term for the Higgs field, identified with some of the fifth dimensional components of the gauge field, is generated, which would be quadratically divergent in the five-dimensional ultraviolet cutoff. This opens the possibility of studying these theories non-perturbatively in order to establish if they can be used as effective weakly interacting theories at low energies. We make preparations for a study on the lattice. In particular we show that only Dirichlet boundary conditions are needed, which specify the breaking pattern of the gauge group at the orbifold fixpoints.

The simplest Gauge-Higgs Unification model is a five-dimensional SU(2) gauge theory compactified ... more The simplest Gauge-Higgs Unification model is a five-dimensional SU(2) gauge theory compactified on the S^1/Z_2 orbifold, such that on the four-dimensional boundaries of space-time there is an unbroken U(1) symmetry and a complex scalar, the latter identified with the Higgs boson. Perturbatively the U(1) remains spontaneously unbroken. Earlier lattice Monte Carlo simulations revealed however that the spontaneous breaking of the U(1) does occur at the non-perturbative level. Here, we verify the Monte Carlo result via an analytical lattice Mean-Field expansion.

We construct a Z 2 orbifold projection of SU (N ) gauge theories formulated in five dimensions wi... more We construct a Z 2 orbifold projection of SU (N ) gauge theories formulated in five dimensions with a compact fifth dimension. We show through a non-perturbative argument that no boundary terms diverging with powers of the five-dimensional ultraviolet cutoff are generated. This opens the possibility of studying these theories nonperturbatively in order to establish if they can be used as effective weakly interacting theories at low energies.

A possible extension of the Standard Model of elementary particles is Gauge-Higgs unification, wh... more A possible extension of the Standard Model of elementary particles is Gauge-Higgs unification, where the Higgs field is identified with (some of) the extra dimensional components of a fivedimensional gauge field. In this scenario there is evidence for the potential and the mass of the Higgs field to be finite. Here we show the behavior of the static potential of a five-dimensional SU(2) lattice gauge theory with orbifold boundary conditions. The potentials are computed within the mean-field approximation including first order corrections.

Journal of High Energy Physics, 2015

We study the viability of five-dimensional gauge theories as candidates for the origin of the Hig... more We study the viability of five-dimensional gauge theories as candidates for the origin of the Higgs field and its mechanism for spontaneous symmetry breaking. Within the framework of lattice field theory, we consider the simplest model of an SU (2) gauge theory. We construct this theory on a five-dimensional orbifold which explicitly breaks the gauge symmetry to U (1) at the fixed points of the orbifold. Using anisotropic gauge couplings, we find that this theory exhibits three distinct phases which we label as confined, Higgs and hybrid. Within the Higgs phase, close to the Higgs-hybrid phase transition, we find that the ratio of the Higgs to gauge boson masses takes Standard Model-like values. Precisely in this region of the phase diagram, we find dimensional reduction via localisation.

Physical Review D, 2012

We examine the static potential in the presence of flavors in the perturbative backreacted D4/D8 ... more We examine the static potential in the presence of flavors in the perturbative backreacted D4/D8 system from localized D8 branes, focusing in particular on the Sakai-Sugimoto model. For the case of long strings we find the flavor corrections to the static potential which are of exponential form. We then investigate shorter Wilson loops and express their energy analytically in terms of the lengths of two neighboring Wilson loops. Moreover, we find that beyond a certain scale the static force in the backreacted background is reduced compared to one in the probe limit, as expected due to screening effects. We also compare the string world-sheets in the two backgrounds and find how they get modified by the backreaction. Our results are supported by numerical computations as well. Finally we discuss our results in comparison with the lattice data and comment on the issue of physical scales which seem to lie at the heart of the reason that obstructs our model at this level to fully describe QCD.

The Standard Model Higgs boson can be identified with the extra dimensional component of a gauge ... more The Standard Model Higgs boson can be identified with the extra dimensional component of a gauge boson in a higher dimensional theory where the gauge group is broken to the Standard Model group by the orbifold action. In that case the Standard Model symmetry can be radiatively broken by the Hosotani mechanism and the Higgs boson mass is protected from bulk quadratic divergences by the higher dimensional gauge theory without any need of supersymmetry. However the latter does not protect a priori the Higgs mass from brane quadratic divergences. We show by an explicit calculation in the orbifold S1/Z_2S^1/Z_2S1/Z_2 that such effects are absent at one-loop. Moreover we identify the symmetry that protects such brane mass terms to all orders in perturbation theory and thus guarantees the absence of a corresponding mass counterterm

Journal of High Energy Physics, 2014

We consider pure SU(N) gauge theories defined on an orbifold lattice, analogous to the S 1 /Z 2 g... more We consider pure SU(N) gauge theories defined on an orbifold lattice, analogous to the S 1 /Z 2 gauge theory orbifolds of the continuum, which according to the perturbative analysis do not have a Higgs phase. Non-perturbatively the conclusion for N even is the opposite, namely that spontaneous symmetry breaking does take place and some of the gauge bosons become massive. We interpret this new, non-perturbative phenomenon both mathematically and physically.

We present a construction of non-Abelian gauge theories on the R^4 x S^1/Z_2 orbifold. We show th... more We present a construction of non-Abelian gauge theories on the R^4 x S^1/Z_2 orbifold. We show that no divergent boundary mass term for the Higgs field, identified with some of the fifth dimensional components of the gauge field, is generated. The formulation of the theories on the lattice requires only Dirichlet boundary conditions that specify the breaking of the gauge group. The first simulations in order to resolve the issue whether these theories can be used at low energy as weakly interacting effective theories have been performed. In case of a positive answer, these theories could provide us with a new framework for studying electroweak symmetry breaking.

Lattice simulations of five-dimensional gauge theories on an orbifold revealed that there is spon... more Lattice simulations of five-dimensional gauge theories on an orbifold revealed that there is spontaneous symmetry breaking. Some of the extra-dimensional components of the gauge field play the role of a Higgs field and some of the four-dimensional components become massive gauge bosons. The effect is confirmed by computing the Coleman-Weinberg potential with a cutoff. We compare the results of this computation with the lattice data.

We develop a method for relating the boundary effective action associated with an orbifold of the... more We develop a method for relating the boundary effective action associated with an orbifold of the D+1 dimensional theory of a p-form field to D dimensional fluxed Chern-Simons type of terms. We apply the construction to derive from twelve dimensions the Chern-Simons terms of the eleven dimensional supergravity theory in the presence of flux.

We analyse non-perturbatively a five-dimensional SU(2) gauge theory compactified on the S^1/Z_2 o... more We analyse non-perturbatively a five-dimensional SU(2) gauge theory compactified on the S^1/Z_2 orbifold. In particular, we present simulation results for the mass spectrum of the theory, which contains a Higgs and a photon. The Higgs mass is found to be free of divergences without fine-tuning. The photon mass is non-zero, thus providing us with the first lattice evidence for a Higgs mechanism derived from an extra dimension. Data from the static potential are consistent with dimensional reduction at low energies.

The effective field theory of the minimal Low Scale Orientifold Models is developed. It describes... more The effective field theory of the minimal Low Scale Orientifold Models is developed. It describes universal features of related orientifold vacua in string theory. It contains, beyond the Standard Model fields, an MSSM-like Higgs sector and three anomalous (massive) U(1) gauge bosons. All renormalizable couplings are included as well as some dimension-five couplings that are important for anomaly cancellation. The Higgs symmetry breaking induces mixing between the anomalous U(1) gauge bosons and the photon and Z 0 . This mixing as well as the anomaly generated cubic vector boson couplings is potentially important for discriminating such models from other theories containing Z's. Some interesting tree-level processes are also evaluated.

We study a five-dimensional pure SU(2) gauge theory formulated on the orbifold and discretized on... more We study a five-dimensional pure SU(2) gauge theory formulated on the orbifold and discretized on the lattice by means of Monte Carlo simulations. The gauge symmetry is explicitly broken to U(1) at the orbifold boundaries. The action is the Wilson plaquette action with a modified weight for the boundary U(1) plaquettes. We study the phase transition and present results for the spectrum and the shape of the static potential on the boundary. The latter is sensitive to the presence of a massive Z-boson, in good agreement with the directly measured Z-boson mass. The results may support an alternative view of the lattice orbifold (stemming from its mean-field study) as a 5d bosonic superconductor.

We study non-perturbatively five-dimensional SU(2) gauge theories by means of the mean-field expa... more We study non-perturbatively five-dimensional SU(2) gauge theories by means of the mean-field expansion on the lattice. On the anisotropic torus we show that a continuum limit can be defined where the anisotropy is a relevant parameter. The analysis of the static force supports the fact that the four-dimensional hyperplanes decouple from each other in the continuum limit. Clear signs of confinement are found in the static potential along the hyperplanes. We present first results from Monte Carlo simulations on the phase diagram.

We present an extension of the Standard Model inspired by the E_8 x E_8 Heterotic String. In orde... more We present an extension of the Standard Model inspired by the E_8 x E_8 Heterotic String. In order that a reasonable effective Lagrangian is presented we neglect everything else other than the ten-dimensional N=1 supersymmetric Yang-Mills sector associated with one of the gauge factors and certain couplings necessary for anomaly cancellation. We consider a compactified space-time M_4 x B_0 / Z_3, where B_0 is the nearly-Kaehler manifold SU(3)/U(1) x U(1) and Z_3 is a freely acting discrete group on B_0. Then we reduce dimensionally the E_8 on this manifold and we employ the Wilson flux mechanism leading in four dimensions to an SU(3)^3 gauge theory with the spectrum of a N=1 supersymmetric theory. We compute the effective four-dimensional Lagrangian and demonstrate that an extension of the Standard Model is obtained with interesting features including a conserved baryon number and fixed tree level Yukawa couplings and scalar potential. The spectrum contains new states such as right ...

These proceedings collect the presentations given at the first three meetings of the INFN "W... more These proceedings collect the presentations given at the first three meetings of the INFN "Workshop on Monte Carlo's, Physics and Simulations at the LHC", held at the Frascati National Laboratories in 2006. The first part of these proceedings contains pedagogical introductions to several basic topics of both theoretical and experimental high pT LHC physics. The second part collects more specialised presentations.

Nuclear Physics B, 2005

We study the effect of Scherk-Schwarz deformations on intersecting branes. Non-chiral fermions in... more We study the effect of Scherk-Schwarz deformations on intersecting branes. Non-chiral fermions in any representation of the Chan-Paton gauge group generically acquire a treelevel mass dependent on the compactification radius and the brane wrapping numbers.

Nucl Phys B, 2005

We construct a Z_2 orbifold projection of SU(N) gauge theories formulated in five dimensions with... more We construct a Z_2 orbifold projection of SU(N) gauge theories formulated in five dimensions with a compact fifth dimension. We show through a non-perturbative argument that no boundary mass term for the Higgs field, identified with some of the fifth dimensional components of the gauge field, is generated, which would be quadratically divergent in the five-dimensional ultraviolet cutoff. This opens the possibility of studying these theories non-perturbatively in order to establish if they can be used as effective weakly interacting theories at low energies. We make preparations for a study on the lattice. In particular we show that only Dirichlet boundary conditions are needed, which specify the breaking pattern of the gauge group at the orbifold fixpoints.

The simplest Gauge-Higgs Unification model is a five-dimensional SU(2) gauge theory compactified ... more The simplest Gauge-Higgs Unification model is a five-dimensional SU(2) gauge theory compactified on the S^1/Z_2 orbifold, such that on the four-dimensional boundaries of space-time there is an unbroken U(1) symmetry and a complex scalar, the latter identified with the Higgs boson. Perturbatively the U(1) remains spontaneously unbroken. Earlier lattice Monte Carlo simulations revealed however that the spontaneous breaking of the U(1) does occur at the non-perturbative level. Here, we verify the Monte Carlo result via an analytical lattice Mean-Field expansion.

We construct a Z 2 orbifold projection of SU (N ) gauge theories formulated in five dimensions wi... more We construct a Z 2 orbifold projection of SU (N ) gauge theories formulated in five dimensions with a compact fifth dimension. We show through a non-perturbative argument that no boundary terms diverging with powers of the five-dimensional ultraviolet cutoff are generated. This opens the possibility of studying these theories nonperturbatively in order to establish if they can be used as effective weakly interacting theories at low energies.

A possible extension of the Standard Model of elementary particles is Gauge-Higgs unification, wh... more A possible extension of the Standard Model of elementary particles is Gauge-Higgs unification, where the Higgs field is identified with (some of) the extra dimensional components of a fivedimensional gauge field. In this scenario there is evidence for the potential and the mass of the Higgs field to be finite. Here we show the behavior of the static potential of a five-dimensional SU(2) lattice gauge theory with orbifold boundary conditions. The potentials are computed within the mean-field approximation including first order corrections.

Journal of High Energy Physics, 2015

We study the viability of five-dimensional gauge theories as candidates for the origin of the Hig... more We study the viability of five-dimensional gauge theories as candidates for the origin of the Higgs field and its mechanism for spontaneous symmetry breaking. Within the framework of lattice field theory, we consider the simplest model of an SU (2) gauge theory. We construct this theory on a five-dimensional orbifold which explicitly breaks the gauge symmetry to U (1) at the fixed points of the orbifold. Using anisotropic gauge couplings, we find that this theory exhibits three distinct phases which we label as confined, Higgs and hybrid. Within the Higgs phase, close to the Higgs-hybrid phase transition, we find that the ratio of the Higgs to gauge boson masses takes Standard Model-like values. Precisely in this region of the phase diagram, we find dimensional reduction via localisation.

Physical Review D, 2012

We examine the static potential in the presence of flavors in the perturbative backreacted D4/D8 ... more We examine the static potential in the presence of flavors in the perturbative backreacted D4/D8 system from localized D8 branes, focusing in particular on the Sakai-Sugimoto model. For the case of long strings we find the flavor corrections to the static potential which are of exponential form. We then investigate shorter Wilson loops and express their energy analytically in terms of the lengths of two neighboring Wilson loops. Moreover, we find that beyond a certain scale the static force in the backreacted background is reduced compared to one in the probe limit, as expected due to screening effects. We also compare the string world-sheets in the two backgrounds and find how they get modified by the backreaction. Our results are supported by numerical computations as well. Finally we discuss our results in comparison with the lattice data and comment on the issue of physical scales which seem to lie at the heart of the reason that obstructs our model at this level to fully describe QCD.

The Standard Model Higgs boson can be identified with the extra dimensional component of a gauge ... more The Standard Model Higgs boson can be identified with the extra dimensional component of a gauge boson in a higher dimensional theory where the gauge group is broken to the Standard Model group by the orbifold action. In that case the Standard Model symmetry can be radiatively broken by the Hosotani mechanism and the Higgs boson mass is protected from bulk quadratic divergences by the higher dimensional gauge theory without any need of supersymmetry. However the latter does not protect a priori the Higgs mass from brane quadratic divergences. We show by an explicit calculation in the orbifold S1/Z_2S^1/Z_2S1/Z_2 that such effects are absent at one-loop. Moreover we identify the symmetry that protects such brane mass terms to all orders in perturbation theory and thus guarantees the absence of a corresponding mass counterterm

Journal of High Energy Physics, 2014

We consider pure SU(N) gauge theories defined on an orbifold lattice, analogous to the S 1 /Z 2 g... more We consider pure SU(N) gauge theories defined on an orbifold lattice, analogous to the S 1 /Z 2 gauge theory orbifolds of the continuum, which according to the perturbative analysis do not have a Higgs phase. Non-perturbatively the conclusion for N even is the opposite, namely that spontaneous symmetry breaking does take place and some of the gauge bosons become massive. We interpret this new, non-perturbative phenomenon both mathematically and physically.

We present a construction of non-Abelian gauge theories on the R^4 x S^1/Z_2 orbifold. We show th... more We present a construction of non-Abelian gauge theories on the R^4 x S^1/Z_2 orbifold. We show that no divergent boundary mass term for the Higgs field, identified with some of the fifth dimensional components of the gauge field, is generated. The formulation of the theories on the lattice requires only Dirichlet boundary conditions that specify the breaking of the gauge group. The first simulations in order to resolve the issue whether these theories can be used at low energy as weakly interacting effective theories have been performed. In case of a positive answer, these theories could provide us with a new framework for studying electroweak symmetry breaking.

Lattice simulations of five-dimensional gauge theories on an orbifold revealed that there is spon... more Lattice simulations of five-dimensional gauge theories on an orbifold revealed that there is spontaneous symmetry breaking. Some of the extra-dimensional components of the gauge field play the role of a Higgs field and some of the four-dimensional components become massive gauge bosons. The effect is confirmed by computing the Coleman-Weinberg potential with a cutoff. We compare the results of this computation with the lattice data.

We develop a method for relating the boundary effective action associated with an orbifold of the... more We develop a method for relating the boundary effective action associated with an orbifold of the D+1 dimensional theory of a p-form field to D dimensional fluxed Chern-Simons type of terms. We apply the construction to derive from twelve dimensions the Chern-Simons terms of the eleven dimensional supergravity theory in the presence of flux.

We analyse non-perturbatively a five-dimensional SU(2) gauge theory compactified on the S^1/Z_2 o... more We analyse non-perturbatively a five-dimensional SU(2) gauge theory compactified on the S^1/Z_2 orbifold. In particular, we present simulation results for the mass spectrum of the theory, which contains a Higgs and a photon. The Higgs mass is found to be free of divergences without fine-tuning. The photon mass is non-zero, thus providing us with the first lattice evidence for a Higgs mechanism derived from an extra dimension. Data from the static potential are consistent with dimensional reduction at low energies.

The effective field theory of the minimal Low Scale Orientifold Models is developed. It describes... more The effective field theory of the minimal Low Scale Orientifold Models is developed. It describes universal features of related orientifold vacua in string theory. It contains, beyond the Standard Model fields, an MSSM-like Higgs sector and three anomalous (massive) U(1) gauge bosons. All renormalizable couplings are included as well as some dimension-five couplings that are important for anomaly cancellation. The Higgs symmetry breaking induces mixing between the anomalous U(1) gauge bosons and the photon and Z 0 . This mixing as well as the anomaly generated cubic vector boson couplings is potentially important for discriminating such models from other theories containing Z's. Some interesting tree-level processes are also evaluated.

We study a five-dimensional pure SU(2) gauge theory formulated on the orbifold and discretized on... more We study a five-dimensional pure SU(2) gauge theory formulated on the orbifold and discretized on the lattice by means of Monte Carlo simulations. The gauge symmetry is explicitly broken to U(1) at the orbifold boundaries. The action is the Wilson plaquette action with a modified weight for the boundary U(1) plaquettes. We study the phase transition and present results for the spectrum and the shape of the static potential on the boundary. The latter is sensitive to the presence of a massive Z-boson, in good agreement with the directly measured Z-boson mass. The results may support an alternative view of the lattice orbifold (stemming from its mean-field study) as a 5d bosonic superconductor.

We study non-perturbatively five-dimensional SU(2) gauge theories by means of the mean-field expa... more We study non-perturbatively five-dimensional SU(2) gauge theories by means of the mean-field expansion on the lattice. On the anisotropic torus we show that a continuum limit can be defined where the anisotropy is a relevant parameter. The analysis of the static force supports the fact that the four-dimensional hyperplanes decouple from each other in the continuum limit. Clear signs of confinement are found in the static potential along the hyperplanes. We present first results from Monte Carlo simulations on the phase diagram.

We present an extension of the Standard Model inspired by the E_8 x E_8 Heterotic String. In orde... more We present an extension of the Standard Model inspired by the E_8 x E_8 Heterotic String. In order that a reasonable effective Lagrangian is presented we neglect everything else other than the ten-dimensional N=1 supersymmetric Yang-Mills sector associated with one of the gauge factors and certain couplings necessary for anomaly cancellation. We consider a compactified space-time M_4 x B_0 / Z_3, where B_0 is the nearly-Kaehler manifold SU(3)/U(1) x U(1) and Z_3 is a freely acting discrete group on B_0. Then we reduce dimensionally the E_8 on this manifold and we employ the Wilson flux mechanism leading in four dimensions to an SU(3)^3 gauge theory with the spectrum of a N=1 supersymmetric theory. We compute the effective four-dimensional Lagrangian and demonstrate that an extension of the Standard Model is obtained with interesting features including a conserved baryon number and fixed tree level Yukawa couplings and scalar potential. The spectrum contains new states such as right ...

These proceedings collect the presentations given at the first three meetings of the INFN "W... more These proceedings collect the presentations given at the first three meetings of the INFN "Workshop on Monte Carlo's, Physics and Simulations at the LHC", held at the Frascati National Laboratories in 2006. The first part of these proceedings contains pedagogical introductions to several basic topics of both theoretical and experimental high pT LHC physics. The second part collects more specialised presentations.

Nuclear Physics B, 2005

We study the effect of Scherk-Schwarz deformations on intersecting branes. Non-chiral fermions in... more We study the effect of Scherk-Schwarz deformations on intersecting branes. Non-chiral fermions in any representation of the Chan-Paton gauge group generically acquire a treelevel mass dependent on the compactification radius and the brane wrapping numbers.