54749102
Lower limits on the strengths of gamma ray lines from WIMP dark matter annihilation
We study the spectra of gamma ray signals that arise from dark matter annihilation in the Universe. We focus on the large class of theories where the photon spectrum includes both continuum spectrum of gamma rays that arise from annihilation into standard model states at tree level, as well as monochromatic gamma rays arising from annihilation directly into two photons at the one-loop level. In this class of theories we obtain lower bounds on the ratio of the strength of the gamma ray line relative to the gamma ray continuum as a function of the dark matter mass and spin. These limits are obtained from the unitarity relation between the tree-level amplitude of the primary annihilation channel and the imaginary part of the loop-level amplitude for annihilation directly into photons, with the primary decay products running in the loop. These results are exact in the limit that dark matter annihilation at tree level is exclusively to a single standard model species, occurs through the lowest partial wave and respects $CP$. Away from this limit the bounds are approximate. Our conclusions agree with known results in the literature for the cases of the minimal supersymmetric standard model, universal extra dimensions and the littlest Higgs with $T$ parity. We use the Fermi-LAT observations to translate these limits into upper bounds on the dark matter annihilation cross section into any specific standard model state.
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).
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.
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...
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.
55183340
Production of a KK-graviton in association with a boson via gluon fusion at the LHC
We discuss the processes where a KK-graviton ($G$) of the extra-dimensional models is produced in association with a color singlet boson via gluon fusion at the LHC. In particular, we consider the processes $gg \to h G$, $\gamma G$, $Z G$. These processes occur at one-loop through box and triangle diagrams. The cross-section for the process $gg \to \gamma G$ vanishes at the one-loop level. It can be understood by introducing the charge conjugation transformations of the KK-graviton. The processes $gg \to h G$, $Z G$ can be observed at the LHC if the KK-graviton and the Higgs boson exist with appropriate properties.
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.
1968264
Production of two photons and a jet through gluon fusion
We have computed the cross-section and distributions for the production of two photons and a jet via the process gg ! g. In the Standard Model, this process occurs at the one-loop level through pentagon and box diagrams. We show that at the LHC this is a signicant mechanism for the production of the two photons and a jet. This process is also an important background to the Higgs boson production, when the Higgs boson decays into two photons. We also explore this process at the Tevatron.
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.
122943004
Looking for a higgs boson of intermediate mass
Abstract It is pointed out that the ability to identify and reconstruct bottoms jets will be important for the identification of the Higgs boson at hadron colliders, if its mass is in the intermediate mass range (2 M W > M H > M Z ). We examine a particular tagging scheme.