Lattice supersymmetry, superfields and renormalization

We study Euclidean lattice formulations of non-gauge supersymmetric models with up to four supercharges in various dimensions. We formulate the conditions under which the interacting lattice theory can exactly preserve one or more nilpotent anticommuting supersymmetries. We introduce a superfield formalism, which allows the enumeration of all possible lattice supersymmetry invariants. We use it to discuss the formulation of Q-exact lattice actions and their renormalization in a general manner. In some examples, one exact supersymmetry guarantees finiteness of the continuum limit of the lattice theory. As a consequence, we show that the desired quantum continuum limit is obtained without fine tuning for these models. Finally, we discuss the implications and possible further applications of our results to the study of gauge and non-gauge models.Comment: 44 pages, 1 figur

SUSY Resonances from UHE neutralinos in Neutrino Telescopes and in the Sky

In the Top-down scenarios, the decay of super-heavy particles (m~10^{12-16}GeV), situated in dark-matter halos not very far from our Galaxy, can explain the ultra-high-energy (UHE) cosmic-ray spectrum beyond the Griesen-Zatasepin-Kuzmin cut-off. In the MSSM, a major component of the UHE cosmic-ray flux at PeV-EeV energies could be given by the lightest neutralino \chi, that is the lightest stable supersymmetric particle. Then, the signal of UHE \chi's on earth might emerge over the interactions of a comparable neutrino component. We compute the event rates for the resonant production of "right" selectrons and "right" squarks in mSUGRA, when UHE neutralinos of energy larger than 10^5 GeV scatter off electrons and quarks in an earth-based detector like IceCube. When the resonant channel dominates in the total \chi-e,\chi-q scattering cross section, the only model parameters affecting the corresponding visible signal rates turn out to be the physical masses of the resonant right-scalar and of the lightest neutralino. We compare the expected number of supersymmetric events with the rates corresponding to the expected Glashow W resonance and to the continuum UHE \nu-N scattering for realistic power-law spectra. We find that the event rate in the leptonic selectron channel is particularly promising, and can reach a few tens for a one-year exposure in IceCube. Finally, we note that UHE neutralinos at much higher energies (up to hundreds ZeV) may produce sneutrino resonances by scattering off relic neutrinos in the Local Group hot dark halo. The consequent \tilde{\nu}-burst into hadronic final states could mimic Z-burst events, although with quite smaller conversion efficiency.Comment: 23 pages, 4 figures; one reference adde

D terms from D-branes, gauge invariance and moduli stabilization in flux compactifications

We elucidate the structure of D terms in N=1 orientifold compactifications with fluxes. As a case study, we consider a simple orbifold of the type-IIA theory with D6-branes at angles, O6-planes and general NSNS, RR and Scherk-Schwarz geometrical fluxes. We examine in detail the emergence of D terms, in their standard supergravity form, from an appropriate limit of the D-brane action. We derive the consistency conditions on gauged symmetries and general fluxes coming from brane-localized Bianchi identities, and their relation with the Freed-Witten anomaly. We extend our results to other N=1 compactifications and to non-geometrical fluxes. Finally, we discuss the possible role of U(1) D terms in the stabilization of the untwisted moduli from the closed string sector.Comment: 1+31 pages, 1 figur

Supersymmetry Without Prejudice

We begin an exploration of the physics associated with the general CP-conserving MSSM with Minimal Flavor Violation, the pMSSM. The 19 soft SUSY breaking parameters in this scenario are chosen so as to satisfy all existing experimental and theoretical constraints assuming that the WIMP is a conventional thermal relic, ie, the lightest neutralino. We scan this parameter space twice using both flat and log priors for the soft SUSY breaking mass parameters and compare the results which yield similar conclusions. Detailed constraints from both LEP and the Tevatron searches play a particularly important role in obtaining our final model samples. We find that the pMSSM leads to a much broader set of predictions for the properties of the SUSY partners as well as for a number of experimental observables than those found in any of the conventional SUSY breaking scenarios such as mSUGRA. This set of models can easily lead to atypical expectations for SUSY signals at the LHC.Comment: 61 pages, 24 figs. Refs., figs, and text added, typos fixed; This version has reduced/bitmapped figs. For a version with better figs please go to http://www.slac.stanford.edu/~rizz

Collider and Dark Matter Searches in Models with Mixed Modulus-Anomaly Mediated SUSY Breaking

We investigate the phenomenology of supersymmetric models where moduli fields and the Weyl anomaly make comparable contributions to SUSY breaking effects in the observable sector of fields. This mixed modulus-anomaly mediated supersymmetry breaking (MM-AMSB) scenario is inspired by models of string compactification with fluxes, which have been shown to yield a de Sitter vacuum (as in the recent construction by Kachru {\it et al}). The phenomenology depends on the so-called modular weights which, in turn, depend on the location of various fields in the extra dimensions. We find that the model with zero modular weights gives mass spectra characterized by very light top squarks and/or tau sleptons, or where M_1\sim -M_2 so that the bino and wino are approximately degenerate. The top squark mass can be in the range required by successful electroweak baryogenesis. The measured relic density of cold dark matter can be obtained via top squark co-annihilation at low \tan\beta, tau slepton co-annihilation at large \tan\beta or via bino-wino coannihilation. Then, we typically find low rates for direct and indirect detection of neutralino dark matter. However, essentially all the WMAP-allowed parameter space can be probed by experiments at the CERN LHC, while significant portions may also be explored at an e^+e^- collider with \sqrt{s}=0.5--1 TeV. We also investigate a case with non-zero modular weights. In this case, co-annihilation, A-funnel annihilation and bulk annihilation of neutralinos are all allowed. Results for future colliders are qualitatively similar, but prospects for indirect dark matter searches via gamma rays and anti-particles are somewhat better.Comment: 38 pages including 22 EPS figures; latest version posted to conform with published versio

Surveying Standard Model Flux Vacua on T6/Z2×Z2T^6/Z_2\times Z_2

We consider the SU(2)LxSU(2)R Standard Model brane embedding in an orientifold of T6/Z2xZ2. Within defined limits, we construct all such Standard Model brane embeddings and determine the relative number of flux vacua for each construction. Supersymmetry preserving brane recombination in the hidden sector enables us to identify many solutions with high flux. We discuss in detail the phenomenology of one model which is likely to dominate the counting of vacua. While Kahler moduli stabilization remains to be fully understood, we define the criteria necessary for generic constructions to have fixed moduli.Comment: 30 pages, LaTeX, v2: added reference

Probing SUSY CP Violation in Two-Body Stop Decays at the LHC

We study CP asymmetries in two-body decays of top squarks into neutralinos and sleptons at the LHC. These asymmetries are used to probe the CP phases possibly present in the stop and neutralino sector of the Minimal Supersymmetric Standard Model. Taking into account bounds from experimental electric dipole moment searches, we identify areas in the mSUGRA parameter space where CP asymmetries can be sizeable and discuss the feasibility of their observation at the LHC. As a result, potentially detectable CP asymmetries in stop decays at the LHC are found, motivating further detailed experimental studies for probing SUSY CP phases.Comment: 38 pages, 13 figures, error in Yukawa coupling corrected, revised benchmark scenario and figures, JHEP versio

Inflation on an Open Racetrack

We present a variant of warped D-brane inflation by incorporating multiple sets of holomorphically-embedded D7-branes involved in moduli stabilization with extent into a warped throat. The resultant D3-brane motion depends on the D7-brane configuration and the relative position of the D3-brane in these backgrounds. The non-perturbative moduli stabilization superpotential takes the racetrack form, but the additional D3-brane open string moduli dependence provides more flexibilities in model building. For concreteness, we consider D3-brane motion in the warped deformed conifold with the presence of multiple D7-branes, and derive the scalar potential valid for the entire throat. By explicit tuning of the microphysical parameters, we obtain inflationary trajectories near an inflection point for various D7-brane configurations. Moreover, the open racetrack potential admits approximate Minkowski vacua before uplifting. We demonstrate with a concrete D-brane inflation model where the Hubble scale during inflation can exceed the gravitino mass. Finally, the multiple sets of D7-branes present in this open racetrack setup also provides a mechanism to stabilize the D3-brane to metastable vacua in the intermediate region of the warped throat.Comment: 29 pages, 15 figures, pre-print number and references adde

DBI Inflation in the Tip Region of a Warped Throat

Previous work on DBI inflation, which achieves inflation through the motion of a $D3$ brane as it moves through a warped throat compactification, has focused on the region far from the tip of the throat. Since reheating and other observable effects typically occur near the tip, a more detailed study of this region is required. To investigate these effects we consider a generalized warp throat where the warp factor becomes nearly constant near the tip. We find that it is possible to obtain 60 or more e-folds in the constant region, however large non-gaussianities are typically produced due to the small sound speed of fluctuations. For a particular well-studied throat, the Klebanov-Strassler solution, we find that inflation near the tip may be generic and it is difficult to satisfy current bounds on non-gaussianity, but other throat solutions may evade these difficulties.Comment: 26 pages, 1 figure. v1. references added, typos corrected v2. clarifications mad

Warped Reheating in Multi-Throat Brane Inflation

We investigate in some quantitative details the viability of reheating in multi-throat brane inflationary scenarios by estimating and comparing the time scales for the various processes involved. We also calculate within perturbative string theory the decay rate of excited closed strings into KK modes and compare with that of their decay into gravitons; we find that in the inflationary throat the former is preferred. We also find that over a small but reasonable range of parameters of the background geometry, these KK modes will preferably tunnel to another throat (possibly containing the Standard Model) instead of decaying to gravitons due largely to their suppressed coupling to the bulk gravitons. Once tunneled, the same suppressed coupling to the gravitons again allows them to reheat the Standard Model efficiently. We also consider the effects of adding more throats to the system and find that for extra throats with small warping, reheating still seems viable.Comment: 29 pages, 4 figures, discussions on closed string decay expanded, references adde