51840101
Goldstini can give the Higgs a boost
Supersymmetric collider phenomenology depends crucially on whether the lightest observable-sector supersymmetric particle (LOSP) decays, and if so, what the LOSP decay products are. For instance, in SUSY models where the gravitino is lighter than the LOSP, the LOSP decays to its superpartner and a longitudinal gravitino via supercurrent couplings. In this paper, we show that LOSP decays can be substantially modified when there are multiple sectors that break supersymmetry, where in addition to the gravitino there are light uneaten goldstini. As a particularly striking example, a bino-like LOSP can have a near 100% branching fraction to a higgs boson and an uneaten goldstino, even if the LOSP has negligible higgsino fraction. This occurs because the uneaten goldstino is unconstrained by the supercurrent, allowing additional operators to mediate LOSP decay. These operators can be enhanced in the presence of a U(1)R symmetry, leading to copious boosted higgs production in SUSY cascade decays.
118513003
Exotic top partners and Little Higgs
A bstractLittle Higgs models often give rise to top partners beyond the minimal ones necessary for the cancellation of quadratic divergences. We review how this occurs and discuss the phenomenology of these exotic states. We emphasize the possible importance of new pseudo-Nambu-Goldstone bosons in top partner decays. Indeed, cascade decays of exotic top partners may be the best way to discover these new bosons. We illustrate these points with a new Little Higgs construction based on an SO(10)/SO(5)2 coset structure, which fills a gap in the model building literature. These observations motivate new search strategies for top partners at the LHC, including for final states with b-jets and a large multiplicity of electroweak bosons.
7293408
Semi-annihilation of dark matter
We show that the thermal relic abundance of dark matter can be affected by a new type of reaction: semi-annihilation. Semi-annihilation takes the schematic form ψiψj → ψkφ, where ψi are stable dark matter particles and φ is an unstable state. Such reactions are generically present when dark matter is composed of more than one species with “flavor” and/or “baryon” symmetries. We give a complete set of coupled Boltzmann equations in the presence of semi-annihilations, and study two toy models featuring this process. Semi-annihilation leads to non-trivial dark matter dynamics in the early universe, often dominating over ordinary annihilation in determining the relic abundance. This process also has important implications for indirect detection experiments, by enriching the final state spectrum from dark matter (semi-)annihilation in the Milky Way.
30709826
Precision jet substructure from boosted event shapes.
Jet substructure has emerged as a critical tool for LHC searches, but studies so far have relied heavily on shower Monte Carlo simulations, which formally approximate QCD at the leading-log level. We demonstrate that systematic higher-order QCD computations of jet substructure can be carried out by boosting global event shapes by a large momentum Q and accounting for effects due to finite jet size, initial-state radiation (ISR), and the underlying event (UE) as 1/Q corrections. In particular, we compute the 2-subjettiness substructure distribution for boosted Z→qq[over ¯] events at the LHC at next-to-next-to-next-to-leading-log order. The calculation is greatly simplified by recycling known results for the thrust distribution in e(+)e(-) collisions. The 2-subjettiness distribution quickly saturates, becoming Q independent for Q > or approximately equal to 400 GeV. Crucially, the effects of jet contamination from ISR/UE can be subtracted out analytically at large Q without knowing their detailed form. Amusingly, the Q=∞ and Q=0 distributions are related by a scaling by e up to next-to-leading-log order.
603052
Spontaneous Lorentz breaking at high energies
Theories that spontaneously break Lorentz invariance also violate diffeomorphism symmetries, implying the existence of extra degrees of freedom and modifications of gravity. In the minimal model (``ghost condensation'') with only a single extra degree of freedom at low energies, the scale of Lorentz violation cannot be larger than about M ~ 100GeV due to an infrared instability in the gravity sector. We show that Lorentz symmetry can be broken at much higher scales in a non-minimal theory with additional degrees of freedom, in particular if Lorentz symmetry is broken by the vacuum expectation value of a vector field. This theory can be constructed by gauging ghost condensation, giving a systematic effective field theory description that allows us to estimate the size of all physical effects. We show that nonlinear effects become important for gravitational fields with strength Φ1/2 g, where g is the gauge coupling, and we argue that the nonlinear dynamics is free from singularities. We then analyze the phenomenology of the model, including nonlinear dynamics and velocity-dependent effects. The strongest bounds on the gravitational sector come from either black hole accretion or direction-dependent gravitational forces, and imply that the scale of spontaneous Lorentz breaking is M Min(1012GeV, g21015GeV). If the Lorentz breaking sector couples directly to matter, there is a spin-dependent inverse-square law force, which has a different angular dependence from the force mediated by the ghost condensate, providing a distinctive signature for this class of models.
118951198
Neutrino constraints on spontaneous Lorentz violation
We study the effect of spontaneous Lorentz violation on neutrinos. We consider two kinds of effects: static effects, where the neutrino acquires a Lorentz-violating dispersion relation, and dynamic effects, which arise from the interactions of the neutrino with the Goldstone boson of spontaneous Lorentz violation. Static effects are well detailed in the literature. Here, special emphasis is given to the novel dynamic effect of Goldstone-Cerenkov radiation, where neutrinos moving with respect to a preferred rest frame can spontaneously emit Goldstone bosons. We calculate the observable consequences of this process and use them to derive experimental bounds from SN1987A and the CMBR. The bounds derived from dynamic effects are complementary to - and in many cases much stronger than - those obtained from static effects.
121621545
Electromagnetic decay rates of neutral mesons
124645739
Experimental Measurement of K0(L) --> mu+ mu-
117292627
Measurement of the charge asymmetry in the decay eta ---> pi+ pi- pi0
18013346
The central drift chamber for the MARK III detector at SPEAR
Abstract A large cylindrical drift chamber has been constructed for the MARK III detector at SPEAR. The inner layer has a high density of sense wires for the measurement of kinks, vees, and d E d x . The outer layers have a cell design with three sense wires, giving uniform drift behavior and left/right ambiguity resolution within a cell. The chamber has both current division and stereo layers for longitudinal position measurement.
116478167
Study of dalitz-plot distributions of the decays eta ---> pi+ pi- pi0 and eta ---> pi+ pi- gamma