Signals of a Sneutrino (N)LSP at the LHC

The sneutrino is a viable candidate for the NLSP in SUSY spectra with gravitino LSP. In this work we study the collider implications of this possibility. In particular, we investigate whether the LHC can distinguish it (at least, in some cases) from alternative spectra, such as those with a neutralino LSP. We show that there exists a complete family of experimentally allowed and theoretically motivated spectra with sneutrino NLSP, which exhibit very distinctive multilepton signals that are difficult to fake within the MSSM. We study these signals in detail, including the techniques necessary to find them. We demonstrate our analysis approach on simulations incorporating backgrounds.Comment: 41 pages, 13 figures. V2: Tau-tau background added and background discussion in subsection V.C modified. Short discussion about early discovery in subsection V.D added. Minors changes and refs. adde

The Fate of Long-Lived Superparticles with Hadronic Decays after LHC Run 1

Supersymmetry searches at the LHC are both highly varied and highly constraining, but the vast majority are focused on cases where the final-stage visible decays are prompt. Scenarios featuring superparticles with detector-scale lifetimes have therefore remained a tantalizing possibility for sub-TeV SUSY, since explicit limits are relatively sparse. Nonetheless, the extremely low backgrounds of the few existing searches for collider-stable and displaced new particles facilitates recastings into powerful long-lived superparticle searches, even for models for which those searches are highly non-optimized. In this paper, we assess the status of such models in the context of baryonic R-parity violation, gauge mediation, and mini-split SUSY. We explore a number of common simplified spectra where hadronic decays can be important, employing recasts of LHC searches that utilize different detector systems and final-state objects. The LSP/NLSP possibilities considered here include generic colored superparticles such as the gluino and light-flavor squarks, as well as the lighter stop and the quasi-degenerate Higgsino multiplet motivated by naturalness. We find that complementary coverage over large swaths of mass and lifetime is achievable by superimposing limits, particularly from CMS's tracker-based displaced dijet search and heavy stable charged particle searches. Adding in prompt searches, we find many cases where a range of sparticle masses is now excluded from zero lifetime to infinite lifetime with no gaps. In other cases, the displaced searches furnish the only extant limits at any lifetime.Comment: 36 pages, 10 figures, plus appendix and reference

Density Perturbations in Chain Inflation

We consider the model of ``Chain Inflation,'' in which the period of inflation in our universe took the form of a long sequence of quantum tunneling events. We find that in the simplest such scenario, in which the tunneling processes are uniform, approximately 10^4 vacua per e-folding of inflation are required in order that the density perturbations produced are of an acceptable size. We arrive at this conclusion through a combination of analytic and numerical techniques, which could also serve as starting points for calculations with more general sets of assumptions.Comment: 28 pages, 16 figures; v2: corrected typos, increased resolution on D=2+1 data point

Electroweak Splitting Functions and High Energy Showering

We derive the electroweak (EW) collinear splitting functions for the Standard Model, including the massive fermions, gauge bosons and the Higgs boson. We first present the splitting functions in the limit of unbroken SU(2)xU(1) and discuss their general features in the collinear and soft-collinear regimes. We then systematically incorporate EW symmetry breaking (EWSB), which leads to the emergence of additional "ultra-collinear" splitting phenomena and naive violations of the Goldstone-boson Equivalence Theorem. We suggest a particularly convenient choice of non-covariant gauge (dubbed "Goldstone Equivalence Gauge") that disentangles the effects of Goldstone bosons and gauge fields in the presence of EWSB, and allows trivial book-keeping of leading power corrections in the VEV. We implement a comprehensive, practical EW showering scheme based on these splitting functions using a Sudakov evolution formalism. Novel features in the implementation include a complete accounting of ultra-collinear effects, matching between shower and decay, kinematic back-reaction corrections in multi-stage showers, and mixed-state evolution of neutral bosons (gamma/Z/h) using density-matrices. We employ the EW showering formalism to study a number of important physical processes at O(1-10 TeV) energies. They include (a) electroweak partons in the initial state as the basis for vector-boson-fusion; (b) the emergence of "weak jets" such as those initiated by transverse gauge bosons, with individual splitting probabilities as large as O(30%); (c) EW showers initiated by top quarks, including Higgs bosons in the final state; (d) the occurrence of O(1) interference effects within EW showers involving the neutral bosons; and (e) EW corrections to new physics processes, as illustrated by production of a heavy vector boson (W') and the subsequent showering of its decay products.Comment: 67 pages, 12 figures; v2, published in JHEP, some expanded discussions and other minor revision

Pulling Out All the Stops: Searching for RPV SUSY with Stop-Jets

If the lighter stop eigenstate decays directly to two jets via baryonic R-parity violation, it could have escaped existing LHC and Tevatron searches in four-jet events, even for masses as small as 100 GeV. In order to recover sensitivity in the face of increasingly harsh trigger requirements at the LHC, we propose a search for stop pairs in the highly-boosted regime, using the approaches of jet substructure. We demonstrate that the four-jet triggers can be completely bypassed by using inclusive jet-H_T triggers, and that the resulting QCD continuum background can be processed by substructure methods into a featureless spectrum suitable for a data-driven bump-hunt down to 100 GeV. We estimate that the LHC 8 TeV run is sensitive to 100 GeV stops with decays of any flavor at better than 5-sigma level, and could place exclusions up to 300 GeV or higher. Assuming Minimal Flavor Violation and running a b-tagged analysis, exclusion reach may extend up to nearly 400 GeV. Longer-term, the 14 TeV LHC at 300/fb could extend these mass limits by a factor of two, while continuing to improve sensitivity in the 100 GeV region.Comment: 28 pages, 10 figure

The Supersymmetric Fine-Tuning Problem and TeV-Scale Exotic Scalars

A general framework is presented for supersymmetric theories that do not suffer from fine-tuning in electroweak symmetry breaking. Supersymmetry is dynamically broken at a scale \Lambda \approx (10 - 100) TeV, which is transmitted to the supersymmetric standard model sector through standard model gauge interactions. The dynamical supersymmetry breaking sector possesses an approximate global SU(5) symmetry, whose SU(3) x SU(2) x U(1) subgroup is explicitly gauged and identified as the standard model gauge group. This SU(5) symmetry is dynamically broken at the scale \Lambda, leading to pseudo-Goldstone boson states, which we call xyons. We perform a detailed estimate for the xyon mass and find that it is naturally in the multi-TeV region. We study general properties of xyons, including their lifetime, and study their collider signatures. A generic signature is highly ionizing tracks caused by stable charged bound states of xyons, which may be observed at the LHC. We also consider cosmology in our scenario and find that a consistent picture can be obtained. Our framework is general and does not depend on the detailed structure of the Higgs sector, nor on the mechanism of gaugino mass generation.Comment: 53 pages, 7 figure