Flavored Dark Matter: A Review

The current status of flavored dark matter is reviewed. We discuss the main experimental constraints on models of flavored dark matter and survey some possible considerations which are relevant for the constructions of models. We then review the application of existing flavor principles to dark matter, with an emphasis on minimal flavor violation, and discuss implications of flavored dark matter on collider phenomenology.

$Hrightarrow gammagamma$ as a Triangle Anomaly: Possible Implications for the Hierarchy Problem

The Standard Model calculation of $Hrightarrowgammagamma$ has the curious feature of being finite but regulator-dependent. While dimensional regularization yields a result which respects the electromagnetic Ward identities, additional terms which violate gauge invariance arise if the calculation is done setting $d=4$. This discrepancy between the $d=4-epsilon$ and $d=4$ results is recognized as a true ambiguity which must be resolved using physics input; as dimensional regularization respects gauge invariance, the $d=4-epsilon$ calculation is accepted as the correct SM result. However, here we point out another possibility; working in analogy with the gauge chiral anomaly, we note that it is possible that the individual diagrams do violate the electromagnetic Ward identities, but that the gauge-invariance-violating terms cancel when all contributions to $Hrightarrowgammagamma$, both from the SM and from new physics, are included. We thus examine the consequences of the hypothesis that the $d=4$ calculation is valid, but that such a cancellation occurs. We work in general renormalizable gauge, thus avoiding issues with momentum routing ambiguities. We point out that the gauge-invariance-violating terms in $d=4$ arise not just for the diagram containing a SM $W^{pm}$ boson, but also for general fermion and scalar loops, and relate these terms to a lack of shift invariance in Higgs tadpole diagrams. We then derive the analogue of anomaly cancellation conditions, and find consequences for solutions to the hierarchy problem. In particular, we find that supersymmetry obeys these conditions, even if it is softly broken at an arbitrarily high scale.

Dark Matter From Weak Polyplets

The addition of new multiplets of fermions charged under the Standard Model gauge group is investigated, with the aim of identifying a possible dark matter candidate. These fermions are charged under $SU(2)times U(1)$, and their quantum numbers are determined by requiring all new particles to obtain masses via Yukawa couplings and all triangle anomalies to cancel as in the Standard Model; more than one multiplet is required and we refer to such a set of these multiplets as a polyplet. For sufficiently large multiplets, the stability of the dark matter candidate is ensured by an accidental symmetry; for clarity, however, we introduce a model with a particularly simple polyplet structure and stabilize the dark matter by imposing a new discrete symmetry. We then explore the features of this model; constraints from colliders, electroweak precision measurements, the dark matter relic density, and direct detection experiments are considered. We find that the model can accommodate a viable dark matter candidate for large Higgs boson masses; for $m_Hsim 125$ GeV, a subdominant contribution to the dark matter relic density can be achieved.

Flavored Dark Matter in Direct Detection Experiments and at LHC

We consider the possibility that dark matter can communicate with the Standard Model fields via flavor interactions. We take the dark matter to belong to a dark sector which contains at least two types, or flavors, of particles and then hypothesize that the Standard Model fields and dark matter share a common interaction which depends on flavor. As, generically, interaction eigenstates and mass eigenstates need not coincide, we consider both flavor-changing and flavor-conserving interactions. These interactions are then constrained by meson decays, kaon mixing, and current collider bounds, and we examine their relevance for direct detection and LHC.

Light Fermionic Dark Matter and its Possible Detection in Neutrino Experiments

We explore the potential for the direct detection of light fermionic dark matter in neutrino detectors. We consider the possible observation of the process $bar{f} p to e^+ n$, where $f$ is a dark matter fermion, in a model-independent manner. All operators of dimension six or lower which can contribute to this process are listed, and we place constraints on these operators from decays of $f$ which contain $gamma$ rays or electrons. One operator is found which is sufficiently weakly constrained that it could give observable interactions in neutrino detectors. We find that Super-Kamiokande can probe the new physics scale for this operator up to $O(100{TeV})$.

Light Hidden Fermionic Dark Matter in Neutrino Experiments

We consider, in a model-independent framework, the potential for observing dark matter in neutrino detectors through the interaction $bar{f} p to e^+ n$, where $f$ is a dark fermion. Operators of dimension six or less are considered, and constraints are placed on their coefficients using the dark matter lifetime and its decays to states which include $gamma$ rays or $e^+e^-$ pairs. After these constraints are applied, there remains one operator which can possibly contribute to $bar{f} p to e^+ n$ in neutrino detectors at an observable level. We then consider the results from the Super-Kamiokande relic supernova neutrino search and find that Super-K can probe the new physics scale of this interaction up to $O(100mbox{ TeV})$.

Hidden MeV-Scale Dark Matter in Neutrino Detectors

The possibility of direct detection of light fermionic dark matter in neutrino detectors is explored from a model-independent standpoint. We consider all operators of dimension six or lower which can contribute to the interaction $bar{f} p to e^+ n$, where $f$ is a dark Majorana or Dirac fermion. Constraints on these operators are then obtained from the $f$ lifetime and its decays which produce visible $gamma$ rays or electrons. We find one operator which would allow $bar{f} p to e^+ n$ at interesting rates in neutrino detectors, as long as $m_f lesssim m_{pi}$. The existing constraints on light dark matter from relic density arguments, supernova cooling rates, and big-bang nucleosynthesis are then reviewed. We calculate the cross-section for $bar{f} p to e^+ n$ in neutrino detectors implied by this operator, and find that Super-K can probe the new physics scale $Lambda$ for this interaction up to ${cal O}(100 {TeV})$