D-brane Inspired Fermion Mass Textures

In this paper, the issues of the quark mass hierarchies and the Cabbibo Kobayashi Maskawa mixing are analyzed in a class of intersecting D-brane configurations with Standard Model gauge symmetry. The relevant mass matrices are constructed taking into account the constraints imposed by extra abelian symmetries and anomaly cancelation conditions. Possible mass generating mechanisms including perturbative as well as non-perturbative effects are discussed and specific patterns of mass textures are found characterized by the hierarchies of the scales where the various sources contribute. It is argued that the Cholesky decomposition of the mass matrices is the most appropriate way to determine the properties of these fermion mass patterns, while the associated triangular mass matrix form provides a unified description of all phenomenologically equivalent symmetric and non-symmetric mass matrices. An elegant analytic formula is derived for the Cholesky triangular form of the mass matrices where the entries are given as simple functions of the mass eigenstates and the diagonalizing transformation entries. Finally, motivated by the possibility of vanishing zero Yukawa mass entries in several D-brane and F-theory constructions due to the geometry of the internal space, we analyse in detail all possible texture-zeroes mass matrices within the proposed new context. These new texture-zeroes are compared to those existing in the literature while D-brane inspired cases are worked out in detail.Comment: 58 pages, 7 figure

New Experimental Limits on Macroscopic Forces Below 100 Microns

Results of an experimental search for new macroscopic forces with Yukawa range between 5 and 500 microns are presented. The experiment uses 1 kHz mechanical oscillators as test masses with a stiff conducting shield between them to suppress backgrounds. No signal is observed above the instrumental thermal noise after 22 hours of integration time. These results provide the strongest limits to date between 10 and 100 microns, improve on previous limits by as much as three orders of magnitude, and rule out half of the remaining parameter space for predictions of string-inspired models with low-energy supersymmetry breaking. New forces of four times gravitational strength or greater are excluded at the 95% confidence level for interaction ranges between 200 and 500 microns.Comment: 25 Pages, 7 Figures: Minor Correction

Building SO(10) models from F-theory

We revisit local F-theory SO(10) and SU(5) GUTs and analyze their properties within the framework of the maximal underlying E_8 symmetry in the elliptic fibration. We consider the symmetry enhancements along the intersections of seven-branes with the GUT surface and study in detail the embedding of the abelian factors undergoing monodromies in the covering gauge groups. We combine flux data from the successive breaking of SO(10) to SU(5) gauge symmetry and subsequently to the Standard Model one, and further constrain the parameters determining the models' particle spectra. In order to eliminate dangerous baryon number violating operators we propose ways to construct matter parity like symmetries from intrinsic geometric origin. We study implementations of the resulting constrained scenario in specific examples obtained for a variety of monodromies.Comment: 53 page

Discrimination of low missing energy look-alikes at the LHC

The problem of discriminating possible scenarios of TeV scale new physics with large missing energy signature at the Large Hadron Collider (LHC) has received some attention in the recent past. We consider the complementary, and yet unexplored, case of theories predicting much softer missing energy spectra. As there is enough scope for such models to fake each other by having similar final states at the LHC, we have outlined a systematic method based on a combination of different kinematic features which can be used to distinguish among different possibilities. These features often trace back to the underlying mass spectrum and the spins of the new particles present in these models. As examples of "low missing energy look-alikes", we consider Supersymmetry with R-parity violation, Universal Extra Dimensions with both KK-parity conserved and KK-parity violated and the Littlest Higgs model with T-parity violated by the Wess-Zumino-Witten anomaly term. Through detailed Monte Carlo analysis of the four and higher lepton final states predicted by these models, we show that the models in their minimal forms may be distinguished at the LHC, while non-minimal variations can always leave scope for further confusion. We find that, for strongly interacting new particle mass-scale ~600 GeV (1 TeV), the simplest versions of the different theories can be discriminated at the LHC running at sqrt{s}=14 TeV within an integrated luminosity of 5 (30) fb^{-1}.Comment: 40 pages, 10 figures; v2: Further discussions, analysis and one figure added, ordering of certain sections changed, minor modifications in the abstract, version as published in JHE

Deciphering Universal Extra Dimension from the top quark signals at the CERN LHC

Models based on Universal Extra Dimensions predict Kaluza-Klein (KK) excitations of all Standard Model (SM) particles. We examine the pair production of KK excitations of top- and bottom-quarks at the Large Hadron Collider. Once produced, the KK top/bottom quarks can decay to $b$-quarks, leptons and the lightest KK-particle, $\gamma_1$, resulting in 2 $b$-jets, two opposite sign leptons and missing transverse momentum, thereby mimicing top-pair production. We show that, with a proper choice of kinematic cuts, an integrated luminosity of 100 fb$^{-1}$ would allow a discovery for an inverse radius upto $R^{-1} = 750$ GeV.Comment: 18 pages, 14 figures, Accepted for publication in JHE

The anomalous U(1) global symmetry and flavors from an SU(5) x SU(5)′' GUT in Z12−IZ_{12-I} orbifold compactification

In string compactifications, frequently there appears the anomalous U(1) gauge symmetry which belonged to E8$\times$E8 of the heterotic string. This anomalous U(1) gauge boson obtains mass at the compactification scale, just below $10^{18\,}$GeV, by absorbing one pseudoscalar (corresponding to the model-independent axion) from the second rank anti-symmetric tensor field $B_{MN}$. Below the compactification scale, there results a global symmetry U(1)$_{\rm anom}$ whose charge $Q_{\rm anom}$ is the original gauge U(1) charge. This is the most natural global symmetry, realizing the "invisible" axion. This global symmetry U(1)$_{\rm anom}$ is suitable for a flavor symmetry. In the simplest compactification model with the flipped SU(5) grand unification, we calculate all the low energy parameters in terms of the vacuum expectation values of the standard model singlets.Comment: 18 pages, 4 figur

A Distorted MSSM Higgs Sector from Low-Scale Strong Dynamics

We show that when supersymmetry is broken at the TeV scale by strong dynamics, the Higgs sector of the MSSM can be drastically modified. This arises from possible sizeable mixings of the Higgs with the resonances of the strong sector. In particular the mass of the lightest Higgs boson can be significantly above the MSSM bound (~130 GeV). Furthermore only one Higgs doublet is strictly necessary, because the Yukawa couplings can have a very different structure compared to the MSSM. Using the AdS/CFT correspondence electroweak precision observables can be calculated and shown to be below experimental bounds. The most natural way to generate sparticle masses is through mixing with the composite states. This causes the gauginos and Higgsinos to easily obtain Dirac masses around 200 GeV, while scalar masses can be generated either from extra D-terms or also through mixing with the strongly-coupled states. Finally one of the most interesting predictions of these scenarios is the sizeable decay width of the Higgs boson into a very light gravitino (~ 10^{-4} eV) and a Higgsino.Comment: 22 pages, 6 figures; v2: improved discussion of oblique parameters and references adde

New Constraints (and Motivations) for Abelian Gauge Bosons in the MeV-TeV Mass Range

We survey the phenomenological constraints on abelian gauge bosons having masses in the MeV to multi-GeV mass range (using precision electroweak measurements, neutrino-electron and neutrino-nucleon scattering, electron and muon anomalous magnetic moments, upsilon decay, beam dump experiments, atomic parity violation, low-energy neutron scattering and primordial nucleosynthesis). We compute their implications for the three parameters that in general describe the low-energy properties of such bosons: their mass and their two possible types of dimensionless couplings (direct couplings to ordinary fermions and kinetic mixing with Standard Model hypercharge). We argue that gauge bosons with very small couplings to ordinary fermions in this mass range are natural in string compactifications and are likely to be generic in theories for which the gravity scale is systematically smaller than the Planck mass - such as in extra-dimensional models - because of the necessity to suppress proton decay. Furthermore, because its couplings are weak, in the low-energy theory relevant to experiments at and below TeV scales the charge gauged by the new boson can appear to be broken, both by classical effects and by anomalies. In particular, if the new gauge charge appears to be anomalous, anomaly cancellation does not also require the introduction of new light fermions in the low-energy theory. Furthermore, the charge can appear to be conserved in the low-energy theory, despite the corresponding gauge boson having a mass. Our results reduce to those of other authors in the special cases where there is no kinetic mixing or there is no direct coupling to ordinary fermions, such as for recently proposed dark-matter scenarios.Comment: 49 pages + appendix, 21 figures. This is the final version which appears in JHE

Dirichlet Higgs as radion stabilizer in warped compactification

We study implications of generalized non-zero Dirichlet boundary condition along with the ordinary Neumann one on a bulk scalar in the Randall-Sundrum warped compactification. First we show profiles of vacuum expectation value of the scalar under the general boundary conditions. We also investigate Goldberger-Wise mechanism in several setups with the general boundary conditions of the bulk scalar field and find that the mechanism can work under non-zero Dirichlet boundary conditions with appropriate vacuum expectation values. Especially, we show that $SU(2)_R$ triplet Higgs in the bulk left-right symmetric model with custodial symmetry can be identified with the Goldberger-Wise scalar.Comment: 35 pages, 25 figures, published versio