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.
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
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.
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).
119357132
The phenomenology of lepton flavored dark matter
In Flavored Dark Matter theories the dark matter particle carries flavor quantum numbers, and has renormalizable contact interactions with the Standard Model fields. The phenomenology of this scenario depends sensitively on whether dark matter carries lepton flavor, quark flavor or its own internal flavor quantum numbers. For the lepton flavored case, we investigate the implications for direct detection experiments and collider signatures. We show that the region of parameter space which leads to the right abundance for a thermal relic is in general within reach of current direct detection experiments. Focusing on a class of models where dark matter carries tau flavor, we show that in a significant part of parameter space these theories can be discovered above Standard Model backgrounds at the Large Hadron Collider. We also study the extent to which flavor and charge correlations among the final state leptons allows models of this type to be distinguished from theories where dark matter couples to leptons...
53520410
Leptophilic dark matter and the anomalous magnetic moment of the muon
A bstractWe consider renormalizable theories such that the scattering of dark matter off leptons arises at tree level, but scattering off nuclei only arises at loop. In this framework, the various dark matter candidates can be classified by their spins and by the forms of their interactions with leptons. We determine the corrections to the anomalous magnetic moment of the muon that arise from its interactions with dark matter. We then consider the implications of these results for a set of simplified models of leptophilic dark matter. When a dark matter candidate reduces the existing tension between the standard model prediction of the anomalous magnetic moment and the experimental measurement, the region of parameter space favored to completely remove the discrepancy is highlighted. Conversely, when agreement is worsened, we place limits on the parameters of the corresponding simplified model. These bounds and favored regions are compared against the experimental constraints on the simplified model from direct detection and from collider searches. Although these constraints are severe, we find there do exist limited regions of parameter space in these simple theories that can explain the observed anomaly in the muon magnetic moment while remaining consistent with all experimental bounds.
119181725
Gluon fusion contribution to VHj production at hadron colliders
Abstract We study the associated production of an electroweak vector boson and the Higgs boson with a jet via gluon–gluon fusion. At the leading order, these processes occur at one-loop level. The amplitudes of these one-loop processes are gauge invariant and finite. Therefore, their contributions towards the corresponding hadronic cross sections and kinematic distributions can be calculated separately. We present results for the Large Hadron Collider and its discussed upgrades. We find that the gluon–gluon one-loop process gives dominant contribution to the γHj production. We observe a destructive interference effect in the g g → Z H j amplitude. We also find that in the high transverse momentum and central rapidity region, the ZHj production cross section via gluon–gluon fusion becomes comparable to the cross section contributions coming from quark–quark and quark–gluon channels.
16473350
Leptoquark Contribution to the Higgs Boson Production at the LHC Collider
In this report we study how a light-scalar leptoquark could aect the Higgs boson production cross-section at the LHC collider. We construct the most general renormalizable and gauge invariant eective Lagrangian involving the standard model particles and a scalar, isoscalar leptoquark, . The total cross-section for pp ! H + X is then calculated for dierent values of the unknown parameters , m and mH.(Here is the coupling associated with the Higgs-leptoquark interaction.) We nd that if is moderately large and m is around a few hundred GeV, then the cross-section is signicantly larger than the standard model value.
119222959
Multilepton signatures of the Higgs boson through its production in association with a top-quark pair
We consider the possible production of the Higgs Boson in association with a top-quark pair and its subsequent decay into a tau-lepton pair or a W-boson pair. This process can give rise to many signatures of the Higgs boson. These signatures can have electrons, muons, tau jets, bottom jets and/or light flavour jets. We analyze the viability of some of these signatures. We will look at those signatures where the background is minimal. In particular, we explore the viability of the signatures "isolated 4 electron/muon" and "isolated 3 electron/muon + a jet" The jet can be due to a light flavour quark/gluon, a bottom quark, or a tau lepton. Of all these signatures, we find that "isolated 3 electron/muon + a tau jet", with an extra bottom jet, can be an excellent signature of this mode of the Higgs boson production. We show that this signature may be visible within a year, once the Large Hadron Collider (LHC) restarts. Some of the other signatures would also be observable after the LHC accumulates sufficient luminosity.
120022857
On detecting new heavy quarks at hadron colliders
Abstract The implications of the existence of a new quark that is heavy enough so that its decay products include an on-shell W boson are discussed. It is argued that in this case the production and subsequent decay of quark-anti-quark pairs of this new flavor will yield a large enough rate of W + W − →l ± vjj events that the two jet mass distribution associated with events selected by the usual W→l ν signal will exhibit and observable W resonance. This feature could serve as a signal for the presence of new heavy quark production at hadron colliders.
14264444
MORE SIGNATURES OF THE INTERMEDIATE MASS HIGGS BOSON
We examine the potential signatures of the Higgs boson when it decays into a tau–lepton pair. We show that with the proper identification of the tau-jet, this decay mode can lead to the identification of the Higgs boson over most of the intermediate mass range (MW