Non-perturbative mass spectrum of an extra-dimensional orbifold

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.Comment: 4 pages, 3 figure

Anomalous U(1), holomorphy, supersymmetry breaking and dilaton stabilization

We argue that in certain models with family symmetries the implementation of the alignment mechanism for the supression of the flavor changing neutral currents requires mass matrices with holomorphic zeros in the down quark sector. Holomorphic zeros typically open flat directions that potentially spoil the uniqueness of the supersymmetric vacuum. We then present an anomalous U(1) model without holomorphic zeros in the quark sector that can reproduce the fermion mass hierarchies, provided that $\tan{\beta}$ is of order one. To avoid undesired flavor changing neutral currents we propose a supersymmetry breaking mechanism and a dilaton stabilization scenario that result in degenerate squarks at $M\sim M_{GUT}$ and a calculable low energy spectrum. We present the numerical predictions of this model for the Higgs mass for different values of $M$ and $\tan{\beta}$.Comment: 14 pages, no figures; wording of the abstract is change

Bulk and brane radiative effects in gauge theories on orbifolds

We have computed one-loop bulk and brane mass renormalization effects in a five-dimensional gauge theory compactified on the M_4 \times S^1/Z_2 orbifold, where an arbitrary gauge group G is broken by the orbifold action to its subgroup H. The space-time components of the gauge boson zero modes along the H generators span the gauge theory on the orbifold fixed point branes while the zero modes of the higher-dimensional components of the gauge bosons along the G/H generators play the role of Higgs fields with respect to the gauge group H. No quadratic divergences in the mass renormalization of the gauge and Higgs fields are found either in the bulk or on the branes. All brane effects for the Higgs field masses vanish (only wave function renormalization effects survive) while bulk effects are finite and can trigger, depending on the fermionic content of the theory, spontaneous Hosotani breaking of the brane gauge group H. For the gauge fields we do find logarithmic divergences corresponding to mass renormalization of their heavy Kaluza-Klein modes. Two-loop brane effects for Higgs field masses are expected from wave function renormalization brane effects inserted into finite bulk mass corrections.Comment: 31 pages, uses axodraw.sty and mcite.st

Brane Worlds, the Cosmological Constant and String Theory

We argue that traditional methods of compactification of string theory make it very difficult to understand how the cosmological constant becomes zero. String inspired models can give zero cosmological constant after fine tuning but since string theory has no free parameters it is not clear that this is allowed. Brane world scenarios on the other hand while they do not answer the question as to why the cosmological constant is zero do actually allow a choice of integration constants that permit flat four space solutions. In this paper we discuss gauged supergravity realizations of such a world. To the extent that this starting point can be considered a low energy effective action of string theory (and there is some recent evidence supporting this) our model may be considered a string theory realization of this scenario.Comment: 18 pages, 5 figures. Shorter version and a few new comments adde

On the large N limit of SU(N) lattice gauge theories in five dimensions

We develop the necessary tools for computing fluctuations around a mean-field background in the context of SU(N) lattice gauge theories in five dimensions. In particular, expressions for the scalar observable and the Wilson Loop are given. As an application, using these observables we compute a certain quantity k5 that can be viewed as Coulomb's constant in five dimensions. We show that this quantity becomes independent of N in the large N limit. Furthermore, the numerical value of k5 we find for SU(infinity) deviates by 17% from its value predicted by holography.Comment: Discussion adde

New Higgs mechanism from the lattice

Spontaneous symmetry breaking has been observed in lattice simulations of five-dimensional gauge theories on an orbifold. This effect is reproduced by perturbation theory if it is modified to account for a finite cut-off. We present a comparison of lattice and analytic results for bulk gauge group SU(2).Comment: 7 pages, 5 figures. Presented at International Europhysics Conference on High Energy Physics (EPS-HEP2007), Manchester, England, 19-25 Jul 200

Dynamical supersymmetry breaking in a superstring inspired model

We present a dilaton dominated scenario for supersymmetry breaking in a recently constructed realistic superstring inspired model with an anomalous U(1) symmetry. Supersymmetry is broken via gaugino condensation due to a confining SU(Nc) gauge group in the hidden sector. In particular, we find that by imposing on the model the phenomenological constraint of the absence of observed flavor changing neutral currents, there is a range of parameters related to the hidden sector and the Kahler potential for which we obtain a low energy spectrum consistent with present experimental bounds. As an illustrative example, we derive the low energy spectrum of a specific model. We find that the LSP is the lightest neutralino with a mass of 53 GeV and the lightest Higgs has a mass of 104 GeV.Comment: 13 page

The phase diagram of Yang-Mills theory with a compact extra dimension

We present a non-perturbative study of the phase diagram of SU(2) Yang-Mills theory in a five-dimensional spacetime with a compact extra dimension. The non-renormalizable theory is regularized on an anisotropic lattice and investigated through numerical simulations in a regime characterized by a hierarchy between the scale of low-energy physics, the inverse compactification radius, and the cutoff scale. We map out the structure of the phase diagram and the pattern of lines corresponding to fixed values of the ratio between the mass of the fifth component of the gauge field and the non-perturbative mass gap of the four-dimensional modes. We discuss different limits of the model, and comment on the implications of our findings.Comment: 17 pages, 9 figure

The Cosmological Constant in Calabi-Yau 3-fold Compactifications of the Horava-Witten Theory

Brane world scenarios offer a way of setting the cosmological constant to zero after supersymmetry breaking provided there is a sufficient number of adjustable integration constants/parameters. In the case of the Horava-Witten theory compactified on a Calabi-Yau threefold, we argue that it is difficult to find enough freedom to get a zero (or small) cosmological constant after supersymmetry breaking.Comment: 9 page

The Higgs mechanism as a cut-off effect

We compute the Coleman-Weinberg potential with a finite cut-off for pure SU(2) and SU(3) five-dimensional gauge theories compactified on an interval. We show that besides the expected Coulomb phase located at and in the vicinity of the free infrared stable or "trivial" fixed point, the theory possesses also a Higgs phase. We compare the results from the potential computation with lattice data from simulations.Comment: 22 pages, 5 figures; introduction improved, conclusions added, published in JHE