118483239
Signals of inert doublet dark matter in neutrino telescopes
One of the simplest extensions of the standard model that explains the observed abundance of dark matter is the inert doublet model. In this theory a discrete symmetry ensures that the neutral component of an additional electroweak doublet scalar is stable and constitutes a dark matter candidate. As massive bodies such as the Sun and Earth move through the dark matter halo, dark matter particles can become gravitationally trapped in their cores. Annihilations of these particles result in neutrinos, which can potentially be observed with neutrino telescopes. We calculate the neutrino detection rate at these experiments from inert doublet dark matter annihilations in the cores of the Sun and the Earth.
120513086
Flavored Dark Matter
Title of dissertation: FLAVORED DARK MATTER Prateek Agrawal, Doctor of Philosophy, 2012 Dissertation directed by: Professor Zackaria Chacko Department of Physics Astrophysical observations point to the fact that most of the matter density in the universe is in the form of a non-luminous “dark matter”. No particles detected so far satisfy the criteria to be dark matter candidates. If the present day dark matter density is set by thermal freeze out due to the expansion of the universe, then the dark matter particles likely have weak-scale interactions with ordinary matter. This opens up the possibility of detecting them in current experiments. We focus on a novel class of models – flavored dark matter – which contains multiple copies, or flavors, of dark matter particles, in analogy with the three copies of matter particles observed in nature. We classify such models and consider their implications for various dark matter searches. As an example, we choose one specific model with tau flavored dark matter, and consider its prospects for detection at the Large Hadron Collider. FLAVORED DARK MATTER
85504800
WIMPs at the galactic center
Simple models of weakly interacting massive particles (WIMPs) predict dark matter annihilations into pairs of electroweak gauge bosons, Higgses or tops, which through their subsequent cascade decays produce a spectrum of gamma rays. Intriguingly, an excess in gamma rays coming from near the Galactic center has been consistently observed in Fermi data. A recent analysis by the Fermi collaboration confirms these earlier results. Taking into account the systematic uncertainties in the modelling of the gamma ray backgrounds, we show for the first time that this excess can be well fit by these final states. In particular, for annihilations to (WW, ZZ, hh, tt{sup -bar}), dark matter with mass between threshold and approximately (165, 190, 280, 310) GeV gives an acceptable fit. The fit range for bb{sup -bar} is also enlarged to 35 GeV≲m{sub χ}≲165 GeV. These are to be compared to previous fits that concluded only much lighter dark matter annihilating into b, τ, and light quark final states could describe the excess. We demonstrate that simple, well-motivated models of WIMP dark matter including a thermal-relic neutralino of the MSSM, Higgs portal models, as well as other simplified models can explain the excess.
54077204
Identifying dark matter interactions in monojet searches
A bstractWe study the discrimination of quark-initiated jets from gluon-initiated jets in monojet searches for dark matter using the technique of averaged jet energy profiles. We demonstrate our results in the context of effective field theories of dark matter interactions with quarks and gluons, but our methods apply more generally to a wide class of models. Different effective theories of dark matter and the standard model backgrounds each have a characteristic quark/gluon fraction for the leading jet. When used in conjunction with the traditional cut-and-count monojet search, the jet energy profile can be used to set stronger bounds on contact interactions of dark matter. In the event of a discovery of a monojet excess at the 14 TeV LHC, contact interactions between dark matter with quarks or with gluons can be differentiated at the 95% confidence level. For a given rate at the LHC, signal predictions at direct detection experiments for different dark matter interactions can span five orders of magnitude. The ability to identify these interactions allows us to make a tighter connection between LHC searches and direct detection experiments.
117007207
A Classification of Dark Matter Candidates with Primarily Spin-Dependent Interactions with Matter
We perform a model-independent classification of Weakly Interacting Massive Particle (WIMP) dark matter candidates that have the property that their scattering off nucleons is dominated by spin-dependent interactions. We study renormalizable theories where the scattering of dark matter is elastic and arises at tree-level. We show that if the WIMP-nucleon cross section is dominated by spin-dependent interactions the natural dark matter candidates are either Majorana fermions or real vector bosons, so that the dark matter particle is its own anti-particle. In such a scenario, scalar dark matter is disfavored. Dirac fermion and complex vector boson dark matter are also disfavored, except for very specific choices of quantum numbers. We further establish that any such theory must contain either new particles close to the weak scale with Standard Model quantum numbers, or alternatively, a $Z'$ gauge boson with mass at or below the TeV scale. In the region of parameter space that is of interest to current direct detection experiments, these particles naturally lie in a mass range that is kinematically accessible to the Large Hadron Collider (LHC).
116347830
Direct Detection Constraints on Dark Matter Event Rates in Neutrino Telescopes, and Collider Implications
Neutrino telescopes are looking to detect neutrinos produced by the annihilation of weakly interacting massive particle (WIMP) dark matter in the sun. The event rate depends on the dark matter density in the sun, which in turn is dictated by the cross section of WIMPs with nucleons. This however is bounded by direct detection experiments. We use the constraints from these experiments to place model-independent upper bounds on the event rates in neutrino telescopes that apply to any elastic dark matter model. Since the spin-independent WIMP-nucleon cross section is much more tightly constrained than the corresponding spin-dependent cross section, the bounds are much stronger in the former case and are competitive with the current limits from IceCube. If the number of events observed in neutrino telescopes exceeds the upper bound corresponding to spin-independent interactions, the implication is that the cross section of dark matter with nucleons is dominated by spin- dependent interactions. In such a scenario the natural dark matter candidates are Majorana fermions and real vector bosons, so that dark matter particles are their own anti-particles. We show that any such theory that leads to observable event rates at current generation neutrino telescopes will in general contain new particles charged under the Standard Model gauge groups that naturally lie in a mass range that is kinematically accessible to the Large Hadron Collider (LHC).
119254863
Dilepton Signatures of the Higgs Boson with Tau-jet Tagging
We consider the process pp ! t¯. This process can give rise to many signatures of the Higgs boson. The signatures can have electrons, muons and jets. We consider the signatures that have two electrons/muons and jets. Tagging of a tau jet and a bottom jet can help reduce the backgrounds significantly. We show that for the signatures to be useful, it should have at least two tau jets, or same-sign electrons/muons. These requirements reduce the backgrounds due the process with Z-bosons and the production of a pair of top quarks. In particular, we examine the usefulness of the signatures “isolated 2 electrons/muons + a bottom jet + a tau jet (eµ�b)”, ‘isolated 2 electrons/muons + 2 tau jets”, “isolated 2 electrons/muons + 2 bottom jets + a tau jet”, and “isolated 2 electrons/muons + a bottom jet + 2 tau jets”. We find that signatures with two tau jets are useful. The signatures with one tau jet are also useful, if we restrict to same-sign electrons/muons. We show that these signatures may be visible in less than a year, once the Large Hadron Collider (LHC) restarts.
118704070
Multi Vector Boson Production via Gluon Fusion at the LHC
At the LHC, the processes with several particles in the final state occur routinely. These processes provide a new domain to test the Standard Model of particle physics. Due to large gluon luminosity at the LHC, gluon initiated processes will be quite important. We study the production of multi-vector bosons via gluon fusion. In particular we consider the process $ g g \to g \gamma Z $ and compute its cross-section at hadron colliders.
119236521
Associated production of a KK-graviton with a Higgs boson via gluon fusion at the LHC
In order to solve the hierarchy problem, several extra-dimensional models have received considerable attention. We have considered a process where a Higgs boson is produced in association with a KK-graviton (GKK) at the LHC. At the leading order, this process occurs through the gluon fusion mechanism gg→hGKK via a quark loop. We compute the cross section and examine some features of this process in the ADD model. We find that the quark in the loop does not decouple in the large quark-mass limit just as in the case of gg→h process. We compute the cross section of this process for the case of the RS model also. We examine the feasibility of this process being observed at the LHC.
13452281
PROSPECTS OF DISCOVERING THE HIGGS BOSON AT THE TEVATRON
We carry out an event generator based study to evaluate the usefulness of the exclusive signature "e±(μ±) + 2 bottom jets" in discovering the Higgs boson at the Tevatron. Using an event generator, we show that with enough luminosity, one should be able to detect the Higgs boson up to the mass of about 130 GeV. We consider a slightly modified version of the above signature that includes one extra jet. This new signature is more useful because it increases the number of signal events significantly.
118126280
Signatures of the Higgs Boson and Heavy Quarks: Testing the Standard Model Paradigm.