[en] We explore the phenomenology of the localized gravity model of Randall and Sundrum where a 5-dimensional nonfactorizable geometry generates the gauge hierarchy by an exponential function called a warp factor. The Kaluza-Klein (KK) tower of gravitons in this scenario has different properties from those in factorizable models. We derive the KK graviton interactions with the standard model fields and obtain constraints from their direct production at hadron colliders as well as from virtual KK exchanges. We study the KK spectrum in e⁺e^- annihilation and show how to determine the model parameters if the first KK state is observed. (c) 2000 The American Physical Society

[en] The phenomenology of the Randall-Sundrum model of localized gravity is analyzed in detail for the two scenarios where the standard model (SM) gauge and matter fields are either confined to a TeV scale 3-brane or may propagate in a slice of five dimensional anti--de Sitter space. In the latter instance, we derive the interactions of the graviton, gauge, and fermion Kaluza-Klein (KK) states. The resulting phenomenological signatures are shown to be highly dependent on the value of the 5-dimensional fermion mass and differ substantially from the case where the SM fields lie on the TeV-brane. In both scenarios, we examine the collider signatures for direct production of the graviton and gauge KK towers as well as their induced contributions to precision electroweak observables. These direct and indirect signatures are found to play a complementary role in the exploration of the model parameter space. In the case where the SM field content resides on the TeV-brane, we show that the CERN LHC can probe the full parameter space and hence will either discover or exclude this model if the scale of electroweak physics on the 3-brane is less than 10 TeV. We also show that spontaneous electroweak symmetry breaking of the SM must take place on the TeV-brane

[en] We examine the unitarity properties of spontaneously broken noncommutative gauge theories. We find that the symmetry breaking mechanism in the noncommutative standard model of Chaichian et al. leads to an unavoidable violation of tree-level unitarity in gauge boson scattering at high energies. We then study a variety of simplified spontaneously broken noncommutative theories and isolate the source of this unitarity violation. Given the group theoretic restrictions endemic to noncommutative model building, we conclude that it is difficult to build a noncommutative standard model under the Weyl-Moyal approach that preserves unitarity

[en] The generalization of the minimal supersymmetric standard model (MSSM) to the case of four chiral fermion generations (4GMSSM) can lead to significant changes in the phenomenology of the otherwise familiar Higgs sector. In most of the 3GMSSM parameter space, the lighter CP-even h is ∼115-125 GeV and mostly standard model-like while H, A, H^± are all relatively heavy. Furthermore, the ratio of Higgs vacuum expectation values, tanβ, is relatively unconstrained. In contrast to this, in the 4GMSSM, heavy fourth-generation fermion loops drive the masses of h, H, H^± to large values while the CP-odd boson, A, can remain relatively light and tanβ is restricted to the range 1/2 < or approx. tanβ < or approx. 2 due to perturbativity requirements on Yukawa couplings. We explore this scenario in some detail, concentrating on the collider signatures of the light CP-odd Higgs at both the Tevatron and LHC. We find that while gg→A may lead to a potential signal in the τ⁺τ^- channel at the LHC, A might first be observed in the γγ channel due to a highly loop-enhanced cross section that can be more than an order of magnitude greater than that of a SM Higgs for A masses of ∼100-150 GeV and tanβ<1. We find that the CP-even states h, H are highly mixed and can have atypical branching fractions. Precision electroweak constraints, particularly for the light A parameter space region, are examined in detail.

[en] We have recently examined a large number of points in the parameter space of the phenomenological minimal supersymmetric Standard Model (MSSM), the 19-dimensional parameter space of the CP-conserving MSSM with minimal flavor violation. We determined whether each of these points satisfied existing experimental and theoretical constraints. This analysis provides insight into general features of the MSSM without reference to a particular SUSY breaking scenario or any other assumptions at the Grand Unified Theory (GUT) scale. This study opens up new possibilities for supersymmetry (SUSY) phenomenology at colliders as well as in both direct and indirect detection searches for dark matter.

[en] Observational evidence for dark matter stems from its gravitational interactions, and as of yet there has been no evidence for dark matter interacting via other means. We examine models where dark matter interactions are purely gravitational in a Randall-Sundrum background. In particular, the Kaluza-Klein tower of gravitons which result from the warped fifth dimension can provide viable annihilation channels into Standard Model final states, and we find that we can achieve values of the annihilation cross section, < σv >, which are consistent with the observed relic abundance in the case of spin-1 dark matter. As a result, we examine constraints on these models employing both the current photon line and continuum indirect dark matter searches, and assess the prospects of hunting for the signals of such models in future direct and indirect detection experiments.

[en] We attempt to build a model that describes the Fermi galactic gamma-ray excess (FGCE) within a UV-complete Supersymmetric framework; we find this to be highly non-trivial. At the very least a successful Supersymmetric explanation must have several important ingredients in order to fit the data and satisfy other theoretical and experimental constraints. Under the assumption that a single annihilation mediator is responsible for both the observed relic density as well as the FGCE, we show that the requirements are not easily satisfied in many TeV-scale SUSY models, but can be met with some model building effort in the general NMSSM with ∼ 10 parameters beyond the MSSM. We find that the data selects a particular region of the parameter space with a mostly singlino lightest Supersymmetric particle and a relatively light CP-odd Higgs boson that acts as the mediator for dark matter annihilation. We study the predictions for various observables within this parameter space, and find that searches for this light CP-odd state at the LHC, as well as searches for the direct detection of dark matter, are likely to be quite challenging. It is possible that a signature could be observed in the flavor sector; however, indirect detection remains the best probe of this scenario

[en] We present the first detailed, large-scale study of the minimal supersymmetric standard model (MSSM) at the √(s)=500 GeV International Linear Collider (ILC), including full standard model backgrounds and detector simulation. This is the first realistic study of the capabilities of the ILC examining the physics of many distinct points in MSSM parameter space which are not linked to a particular supersymmetry (SUSY) breaking mechanism. Specifically, we investigate 242 points in the MSSM parameter space, which we term models, that correspond to the 162 pairs of models that were found by Arkani-Hamed et al. to give indistinguishable signatures at the LHC. We first determine whether the production of the various SUSY particles is visible above the standard model background for each of these parameter space points, and then make a detailed comparison of their various signatures. Assuming an integrated luminosity of 500 fb^-1 with 80% electron beam polarization, we find that only 82 out of 242 models lead to visible signatures of some kind with a significance ≥5 and that only 57 (63) out of the 162 model pairs are distinguishable at 5 (3)σ. Our analysis includes PYTHIA and CompHEP SUSY signal generation, full matrix element SM backgrounds for all 2→2, 2→4 and 2→6 processes, ILC-specific initial state radiation and beamstrahlung generated via WHIZARD/GuineaPig, and employs the fast SiD detector simulation org.lcsim. If SUSY is light, the ILC will do a good job at examining its details.