2,088 research outputs found
Electroweakino constraints from LHC data
We investigate the sensitivity of existing LHC searches to the charginos and
neutralinos of the MSSM when all the other superpartners are decoupled. In this
limit, the underlying parameter space reduces to a simple four-dimensional set
. We examine the constraints placed on this
parameter space by a broad range of LHC searches taking into account the full
set of relevant production and decay channels. We find that the exclusions
implied by these searches exceed existing limits from LEP only for smaller
values of the Bino mass GeV. Our results have implications
for MSSM dark matter and electroweak baryogenesis.Comment: 30 pages, 15 figure
Extending LHC Coverage to Light Pseudoscalar Mediators and Coy Dark Sectors
Many dark matter models involving weakly interacting massive particles
(WIMPs) feature new, relatively light pseudoscalars that mediate dark matter
pair annihilation into Standard Model fermions. In particular, simple models of
this type can explain the gamma ray excess originating in the Galactic Center
as observed by the Fermi Large Area Telescope. In many cases the pseudoscalar's
branching ratio into WIMPs is suppressed, making these states challenging to
detect at colliders through standard dark matter searches. Here, we study the
prospects for observing these light mediator states at the LHC without
exploiting missing energy techniques. While existing searches effectively probe
pseudoscalars with masses between 5 - 14 GeV and above 90 GeV, the LHC reach
can be extended to cover much of the interesting parameter space in the
intermediate 20 - 80 GeV mass range in which the mediator can have appreciable
Yukawa-like couplings to Standard Model fermions but would have escaped
detection by LEP and other experiments. Models explaining the Galactic Center
excess via a light pseudoscalar mediator can give rise to a promising signal in
this regime through the associated production of the mediator with bottom
quarks while satisfying all other existing constraints. We perform an analysis
of the backgrounds and trigger efficiencies, detailing the cuts that can be
used to extract the signal. A significant portion of the otherwise
unconstrained parameter space of these models can be conclusively tested at the
13 TeV LHC with 100 fb, and we encourage the ATLAS and CMS
collaborations to extend their existing searches to this mass range.Comment: 27 pages + 3 appendices, 20 figures, 7 table
Characterizing Strategic Cascades on Networks
Transmission of disease, spread of information and rumors, adoption of new
products, and many other network phenomena can be fruitfully modeled as
cascading processes, where actions chosen by nodes influence the subsequent
behavior of neighbors in the network graph. Current literature on cascades
tends to assume nodes choose myopically based on the state of choices already
taken by other nodes. We examine the possibility of strategic choice, where
agents representing nodes anticipate the choices of others who have not yet
decided, and take into account their own influence on such choices. Our study
employs the framework of Chierichetti et al. [2012], who (under assumption of
myopic node behavior) investigate the scheduling of node decisions to promote
cascades of product adoptions preferred by the scheduler. We show that when
nodes behave strategically, outcomes can be extremely different. We exhibit
cases where in the strategic setting 100% of agents adopt, but in the myopic
setting only an arbitrarily small epsilon % do. Conversely, we present cases
where in the strategic setting 0% of agents adopt, but in the myopic setting
(100-epsilon)% do, for any constant epsilon > 0. Additionally, we prove some
properties of cascade processes with strategic agents, both in general and for
particular classes of graphs.Comment: To appear in EC 201
Using Final State Pseudorapidities to Improve s-channel Resonance Observables at the LHC
We study the use of final state particle pseudorapidity for measurements of
s-channel resonances at the LHC. Distinguishing the spin of an s-channel
resonance can, in principle, be accomplished using angular distributions in the
centre-of-mass frame, possibly using a centre-edge asymmetry measurement, A_CE.
In addition, forward-backward asymmetry measurements, A_FB, can be used to
distinguish between models of extra neutral gauge bosons. In this note we show
how these measurements can be improved by using simple methods based on the
pseudorapidity of the final state particles and present the expected results
for A_FB and A_CE for several representative models.Comment: 6 pages, 4 figures, 1 table; typos fixed, improved visibility of
figures for greyscale printin
Unravelling an Extra Neutral Gauge Boson at the LHC using Third Generation Fermions
We study the potential to use measurements of extra neutral gauge bosons (Z')
properties in pp collisions at the Large Hadron Collider to unravel the
underlying physics. We focus on the usefulness of third generation final states
(tau, b, t) in distinguishing between models with non-universal Z'-fermion
couplings. We present an update of discovery limits of Z's including the
2010-2011 LHC run and include models with non-universal couplings. We show how
ratios of sigma(pp -> Z' -> ttbar), sigma(pp -> Z' -> bbbar), and sigma(pp ->
Z' -> tau^+tau^-) to sigma(pp -> Z' -> mu^+mu^-) can be used to distinguish
between models and measure parameters of the models. Of specific interest are
models with preferential couplings, such as models with generation dependent
couplings. We also find that forward-backward asymmetry measurements with third
generation fermions in the final state could provide important input to
understanding the nature of the Z'. Understanding detector resolution and
efficiencies will be crucial for extracting results
- β¦