Showing papers by "Neal Weiner published in 2013"

UV completions of magnetic inelastic and Rayleigh dark matter for the Fermi Line(s)

Abstract: Models that seek to produce a line at $\ensuremath{\sim}130\text{ }\text{ }\mathrm{GeV}$ as possibly present in the Fermi data face a number of phenomenological hurdles, not the least of which is achieving the high cross section into $\ensuremath{\gamma}\ensuremath{\gamma}$ required. A simple explanation is a fermionic dark matter particle that couples to photons through loops of charged messengers. We study the size of the dimension-5 dipole (for a pseudo-Dirac state) and dimension-7 Rayleigh operators in such a model, including all higher order corrections in $1/{M}_{\mathrm{mess}}$. Such corrections tend to enhance the annihilation rates beyond the naive effective operators. We find that while freeze-out is generally dominated by the dipole, the present-day gamma-ray signatures are dominated by the Rayleigh operator, except at the most strongly coupled points, motivating a hybrid approach. With this, the magnetic inelastic dark matter scenario provides a successful explanation of the lines at only moderately strong coupling. We also consider the pure Majorana weakly interacting massive particle, where both freeze-out and the Fermi lines can be explained, but only at very strong coupling with light ($\ensuremath{\sim}200--300\text{ }\text{ }\mathrm{GeV}$) messengers. In both cases there is no conflict with nonobservation of continuum photons.

Looking for new charged states at the LHC: Signatures of Magnetic and Rayleigh Dark Matter

Abstract: Magnetic and Rayleigh dark matter are models describing weak interactions of dark matter with electromagnetism through non-renormalizable operators of dimensions 5 and 7, respectively. Such operators motivate the existence of heavier states that couple to dark matter and are also charged under the electroweak interactions. The recent hints of a gamma-ray line in the Fermi data suggest that these states may be light enough to be produced at the LHC. We categorize such states according to their charges and decay modes, and we examine the corresponding LHC phenomenology. We emphasize unconstrained models that can be discovered in targeted searches at the upgraded LHC run, while also enumerating models excluded by current data. Generally, models with SUW (2)-singlet states or models where the charged states decay predominantly to tau leptons and/or gauge bosons are still viable. We propose searches to constrain such models and, in particular, find superior performance over existing proposals for multi-tau analyses. Finally, we note several scenarios, especially those dominated by tau final states, that cannot be probed even with 300/fb at LHC14, motivating the further refinement of tau-lepton searches to improve sensitivity to such final states.

A collective breaking of R-parity

Abstract: Supersymmetric theories with an R-parity generally yield a striking missing energy signature, with cascade decays concluding in a neutralino that escapes the detector. In theories where R-parity is broken the missing energy is replaced with additional jets or leptons, often making traditional search strategies ineffective. Such R-parity violation is very constrained, however, by resulting B and L violating signals. The R-parity violating couplings must be so small that there is tension for LSP decays to occur within the detector, unless couplings to different flavors are strongly hierarchical. In theories with additional matter fields, R-parity can be broken collectively, such that R-parity is not broken by any single coupling, but only by an ensemble of couplings. Cascade decays can proceed normally, with each step only sensitive to one or two couplings at a time, but B and L violation requires the full set, yielding a highly suppressed constraint. s-channel production of new scalar states, typically small for standard RPV, can be large when RPV is broken collectively. While missing energy is absent, making these models difficult to discover by traditional SUSY searches, they produce complicated many object resonances (MORes), with many different possible numbers of jets and leptons. We outline a simple model and discuss its discoverability at the LHC.

Hiding Missing Energy in Missing Energy

Abstract: Searches for supersymmetry (SUSY) often rely on a combination of hard physics objects (jets, leptons) along with large missing transverse energy to separate New Physics from Standard Model hard processes. We consider a class of ``double-invisible'' SUSY scenarios: where squarks, stops and sbottoms have a three-body decay into two (rather than one) invisible final-state particles. This occurs naturally when the LSP carries an additional conserved quantum number under which other superpartners are not charged. In these topologies, the available energy is diluted into invisible particles, reducing the observed missing energy and visible energy. This can lead to sizable changes in the sensitivity of existing searches, dramatically changing the qualitative constraints on superpartners. In particular, for m_LSP>160 GeV, we find no robust constraints from the LHC at any squark mass for any generation, while for lighter LSPs we find significant reductions in constraints. If confirmed by a full reanalysis from the collaborations, such scenarios allow for the possibility of significantly more natural SUSY models. While not realized in the MSSM, such phenomenology occurs naturally in models with mixed sneutrinos, Dirac gauginos and NMSSM-like models.

Looking for new charged states at the LHC: Signatures of Magnetic and Rayleigh Dark Matter

Abstract: Magnetic and Rayleigh dark matter are models describing weak interactions of dark matter with electromagnetism through non-renormalizable operators of dimensions 5 and 7, respectively. Such operators motivate the existence of heavier states that couple to dark matter and are also charged under the electroweak interactions. The recent hints of a gamma-ray line in the Fermi data suggest that these states may be light enough to be produced at the LHC. We categorize such states according to their charges and decay modes, and we examine the corresponding LHC phenomenology. We emphasize unconstrained models that can be discovered in targeted searches at the upgraded LHC run, while also enumerating models excluded by current data. Generally, models with SU(2)-singlet states or models where the charged states decay predominantly to tau leptons and/or gauge bosons are still viable. We propose searches to constrain such models and, in particular, find superior performance over existing proposals for multi-tau analyses. Finally, we note several scenarios, especially those dominated by tau final states, that cannot be probed even with 300/fb at LHC14, motivating the further refinement of tau lepton searches to improve sensitivity to such final states.