Dark matter and supersymmetry in the tera-electronvolt era [electronic resource]

The current era of fundamental particle physics research is driven by experimental data to a degree that has not been seen in decades. The flagship experiments in our field are being performed by the ATLAS and CMS collaborations whose detectors record the results of proton-proton collisions provided by the CERN Large Hadron Collider (LHC) at center-of-mass energies of 7 or 8 tera-electron volts (TeV). This has allowed the first direct test of the Standard Model of Particle Physics (SM) at/above weak-scale energies ($\sim 100\gev$-

3$\% dark energy, $\% ordinary matter. Astronomical data such as stellar rotation curves (the oldest evidence of dark matter) and measurements of the gravitational potential of objects via gravitational lensing all suggest that the dominant matter density in galaxies (such as our own Milky Way) is dark. Recent lensing analyses, the ``Bullet Cluster'' \cite{Clowe:2006eq} in particular, seem to provide solid dynamical proof of the \emph{particulate} nature of the dark matter component of these galaxy clusters\footnote{Such evidence has been particularly difficult to explain in theories without dark matter, such as Modified Newtonian Dynamics (MOND) \cite{p-mond}.}. Despite the depth and breadth of the evidence for dark matter, none of this evidence suggests stronger-than-gravitational interactions between dark matter and the particles of the Standard Model. Possibilities range from the (plausible but extremely difficult to study) case of having \emph{only} gravitational-strength DM-SM interactions to having DM-SM and SM-SM interactions of roughly the strength of the weak-nuclear force (above which there are indirect bounds from the gravitational observations of the effects of dark matter). A very natural expectation then is that the dark matter particle is a particle with roughly weak scale mass coupling to the Standard Model via the weak interaction by exchanging mediating particles that also have mass near the weak scale. This could arise simply via the electroweak interaction if the DM and the mediator come in electroweak multiplets of the SM gauge group $SU(2)_L \otimes U(1)_Y$, as happens in many common examples (like supersymmetry), but may also arise from one of a variety of other possible scenarios (for example, secluded sector models \cite{p-pospelov}, in which the dark sector includes its own force carrier/s and DM-SM interactions can arise via kinetic mixing between these ``dark photons" and the SM photon). Despite the depth and breadth of the evidence for dark matter, none of this evidence suggests stronger-than-gravitational interactions between dark matter and the particles of the Standard Model. Possibilities range from the (plausible but extremely difficult to study) case of having \emph{only} gravitational-strength DM-SM interactions to having DM-SM and SM-SM interactions of roughly the strength of the weak-nuclear force (above which there are indirect bounds from the gravitational observations of the effects of dark matter). A very natural expectation then is that the dark matter particle is a particle with roughly weak scale mass coupling to the Standard Model via the weak interaction by exchanging mediating particles that also have mass near the weak scale. This could arise simply via the electroweak interaction if the DM and the mediator come in electroweak multiplets of the SM gauge group $SU(2)_L \otimes U(1)_Y$, as happens in many common examples (like supersymmetry), but may also arise from one of a variety of other possible scenarios (for example, secluded sector models \cite{p-pospelov}, in which the dark sector includes its own force carrier/s and DM-SM interactions can arise via kinetic mixing between these ``dark photons" and the SM photon). While the study of weakly-interacting massive particle (WIMP) dark matter has flourished because of the expectations for discoveries of new weak-scale particles at the LHC and of signals in direct- and indirect-detection experiments, the WIMP scenario is also motivated theoretically. The ``WIMP Miracle'' is the statement that in a universe with WIMP dark matter ($\ie$, particles having an annihilation cross-section that is $\sim\:10^{-26}\:\rm{cm}^3\:\rm{s}^{-1}$), evolving in thermal equilibrium, more or less naturally generates a relic density of dark matter that is in accord with the measured value $\Omega_{\mathrm{WMAP}}h^2\approx0.11$. This is a non-trivial accomplishment, as evidenced by how difficult it is to actually achieve in realistic WIMP models, but may certainly also be mere coincidence\footnote{A similar line of reasoning points out that the closeness of the dark matter and baryon energy densities (they differ only by a factor of $\sim 5$) suggests that the baryon asymmetry of the universe is related to (perhaps generated by) a dark matter/anti-dark matter asymmetry in the dark sector \cite{p-adm}.}. The best-studied example of Beyond the Standard Model physics that can simultaneously solve the hierarchy problem, provide for grand unification and that includes a WIMP dark matter candidate particle, is supersymmetry (SUSY) \cite{p-mssmrev}. Supersymmetric theories are built out of multiplets of particles having the same mass and gauge quantum numbers, but differing in spin. In a supersymmetric universe we would, for example, observe that there is a negatively charged scalar particle weighing \tev$ and $\sim 10\infb$ at \tev$ data.}). The minimal\footnote{In the sense that the anomalies generated by the addition of chiral fermions can be cancelled.} phenomenological supersymmetric model is the Minimal Supersymmetric Standard Model (MSSM). After the inclusion of the most general set of supersymmetry breaking terms (which still allow for a satisfactory solution to the hierarchy problem) the MSSM is described by more than

Keywords: Physics
Advisor: Hewett JoAnne L. primary advisor. Thesis advisor
Peskin Michael Edward
Silverstein Eva