Determining the Flavour Content of the Low-Energy Solar Neutrino Flux

We study the sensitivity of the HELLAZ and Borexino solar neutrino experiments on discriminating the neutrino species nu_e, anti-nu_e, nu_{mu,tau}, anti-nu_{mu,tau}, and nu_{sterile} using the difference in the recoil electron kinetic energy spectra in elastic neutrino-electron scattering. We find that one can observe a non-vanishing nu_{mu,tau} component in the solar neutrino flux, especially when the nu_e survival probability is low. Also, if the data turn out to be consistent with nu_e nu_{mu,tau} oscillations, an anti-nu_e component can be excluded effectively.Comment: 24 pages, 7 figure

Fake Dark Matter at Colliders

If the dark matter (DM) consists of a weakly interacting massive particle (WIMP), it can be produced and studied at future collider experiments like those at the LHC. The production of collider-stable WIMPs is characterized by hard scattering events with large missing transverse energy. Here we point out that the discovery of this well-characterized DM signal may turn out to be a red herring. We explore an alternative explanation -- fake dark matter -- where the only sources of missing transverse energy are standard model neutrinos. We present examples of such models, focusing on supersymmetric models with R-parity violation. We also briefly discuss means of differentiating fake dark matter from the production of new collider-stable particles.Comment: 11 pages, 3 figures, revtex; references adde

New Chiral Fermions, a New Gauge Interaction, Dirac Neutrinos, and Dark Matter

We propose that all light fermionic degrees of freedom, including the Standard Model (SM) fermions and all possible light beyond-the-standard-model fields, are chiral with respect to some spontaneously broken abelian gauge symmetry. Hypercharge, for example, plays this role for the SM fermions. We introduce a new symmetry, $U(1)_{\nu}$, for all new light fermionic states. Anomaly cancellations mandate the existence of several new fermion fields with nontrivial $U(1)_{\nu}$ charges. We develop a concrete model of this type, for which we show that (i) some fermions remain massless after $U(1)_{\nu}$ breaking -- similar to SM neutrinos -- and (ii) accidental global symmetries translate into stable massive particles -- similar to SM protons. These ingredients provide a solution to the dark matter and neutrino mass puzzles assuming one also postulates the existence of heavy degrees of freedom that act as "mediators" between the two sectors. The neutrino mass mechanism described here leads to parametrically small Dirac neutrino masses, and the model also requires the existence of at least four Dirac sterile neutrinos. Finally, we describe a general technique to write down chiral-fermions-only models that are at least anomaly-free under a $U(1)$ gauge symmetry