Thomas D. Jacques

Searching for Dark Matter at the LHC with a Mono-Z

We investigate a mono-Z process as a potential dark matter search strategy at the LHC. In this channel a single Z boson recoils against missing transverse momentum, attributed to dark matter particles,

Electroweak bremsstrahlung in dark matter annihilation

\chi

Dark matter annihilation signatures from electroweak bremsstrahlung

, which escape the detector. This search strategy is related, and complementary to, monojet and monophoton searches. For illustrative purposes we consider the process

Conservative Constraints on dark matter annihilation into gamma rays

q\bar{q} -> \chi\chi Z

Additional light sterile neutrinos and cosmology

in a toy dark matter model, where the Z boson is emitted from either the initial state quarks, or from the internal propagator. Among the signatures of this process will be a pair of muons with high pT that reconstruct to the invariant mass of the Z, and large amounts of missing transverse energy. Being a purely electroweak signal, QCD and other Standard Model backgrounds are relatively easily removed with modest selection cuts. We compare the signal to Standard Model backgrounds and demonstrate that, even for conservative cuts, there exist regions of parameter space where the signal may be clearly visible above background in future LHC data, allowing either new discovery potential or the possibility of supplementing information about the dark sector beyond that available from other observable channels.

Gamma-ray Constraints on Dark Matter Annihilation into Charged Particles

A conservative upper bound on the total dark matter annihilation rate can be obtained by constraining the appearance rate of the annihilation products which are hardest to detect. The production of neutrinos, via the process {chi}{chi}{yields}{nu}{nu}, has thus been used to set a strong general bound on the dark matter annihilation rate. However, standard model radiative corrections to this process will inevitably produce photons which may be easier to detect. We present an explicit calculation of the branching ratios for the electroweak bremsstrahlung processes {chi}{chi}{yields}{nu}{nu}Z and {chi}{chi}{yields}{nu}eW. These modes inevitably lead to electromagnetic showers and further constraints on the dark matter annihilation cross section. In addition to annihilation, our calculations are also applicable to the case of dark matter decay.

Scientific reach of multiton-scale dark matter direct detection experiments

We examine observational signatures of dark matter annihilation in the Milky Way arising from electroweak bremsstrahlung contributions to the annihilation cross section. It has been known for some time that photon bremsstrahlung may significantly boost DM annihilation yields. Recently, we have shown that electroweak bremsstrahlung of W and Z gauge bosons can be the dominant annihilation channel in some popular models with helicity-suppressed 2 --> 2 annihilation. W/Z-bremsstrahlung is particularly interesting because the gauge bosons produced via annihilation subsequently decay to produce large correlated fluxes of electrons, positrons, neutrinos, hadrons (including antiprotons) and gamma rays, which are all of importance in indirect dark matter searches. Here we calculate the spectra of stable annihilation products produced via gamma/W/Z-bremsstrahlung. After modifying the fluxes to account for the propagation through the Galaxy, we set upper bounds on the annihilation cross section via a comparison with observational data. We show that stringent cosmic ray antiproton limits preclude a sizable dark matter contribution to observed cosmic ray positron fluxes in the class of models for which the bremsstrahlung processes dominate.

Sensitivity of the Cherenkov Telescope Array to the Detection of a Dark Matter Signal in comparison to Direct Detection and Collider Experiments

Using gamma-ray data from observations of the Milky Way, Andromeda (M31), and the cosmic background, we calculate conservative upper limits on the dark matter self-annihilation cross section to monoenergetic gamma rays, _{gamma gamma}, over a wide range of dark matter masses. We focus on the gamma gamma final state, as it would be a very clean signature of dark matter annihilation. As our constraints on the cross section are affected by astrophysical uncertainties, we are conservative in our input choices and analysis methods and show how our results depend on these. Using our upper limits on the dark matter annihilation cross section to gamma rays, and a conservative assumption about the branching ratio to monoenergetic gamma rays, we define upper limits on the total cross section and compare to other constraints.

Neutrino signals from electroweak bremsstrahlung in solar WIMP annihilation

Physics Department, Arizona State University, Tempe AZ, 85287-1404(Dated: January 14, 2013)Tantalizing cosmological and terrestrial evidence suggests the number of light neutrinos may begreater than 3, motivating a careful re-examination of cosmological bounds on extra light species.Big Bang Nucleosynthesis constrains the number of relativistic neutrino species present during nucle-osynthesis, N

Robust constraints on dark matter annihilation into gamma rays and charged particles

Dark matter annihilation into charged particles is necessarily accompanied by gamma rays, produced via radiative corrections. Internal bremsstrahlung from the final state particles can produce hard gamma rays up to the dark matter mass, with an approximately model-independent spectrum. Focusing on annihilation into electrons, we compute robust upper bounds on the dark matter self-annihilation cross section (σ A ν) e + e - using gamma-ray data from the Milky Way spanning a wide range of energies ∼10 -3 -10 4 GeV. We also compute corresponding bounds for the other charged leptons. We make conservative assumptions about the astrophysical inputs, and demonstrate how our derived bounds would be strengthened if stronger assumptions about these inputs are adopted. The fraction of hard gamma rays near the end point accompanying annihilation to e + e - is only a factor of <10 2 lower than for annihilation directly to monoenergetic gamma rays. The bound on (σ A ν) e + e - is thus weaker than that for (σ A ν) γγ by this same factor. The upper bounds on the annihilation cross sections to charged leptons are compared with an upper bound on the total annihilation cross section defined by neutrinos.