Abstract:We propose an alternate, calculable mechanism of dark matter genesis, thermal freeze-in, involving a Feebly Interacting Massive Particle (FIMP) interacting so feebly with the thermal bath that it never attains thermal equilibrium. As with the conventional thermal freeze-out production mechanism, the relic abundance reects a combination of initial thermal distributions together with particle masses and couplings that can be measured in the laboratory or astrophysically. The freeze-in yield is IR dominated by low temperatures near the FIMP mass and is independent of unknown UV physics, such as the reheat temperature after ination. Moduli and modulinos of string theory compactications that receive mass from weak-scale supersymmetry breaking provide implementations of the freeze-in mechanism, as do models that employ Dirac neutrino masses or GUT-scalesuppressed interactions. Experimental signals of freeze-in and FIMPs can be spectacular, including the production of new metastable coloured or charged particles at the LHC as well as the alteration of big bang nucleosynthesis.

The quadratic divergences of the Higgs mass may be cancelled either accidentally or by the exchange of some new particles. Alternatively its impact on naturalness may be weakened by raising the Higgs mass, which requires changing the Standard Model below its natural cut-off. We show in detail how this can be achieved, while preserving perturbativity and consistency with the electroweak precision tests, by extending the Standard Model to include a second Higgs doublet that has neither a vev nor couplings to quarks and leptons. This Inert Doublet Model yields a perturbative and completely natural description of electroweak physics at all energies up to 1.5 TeV. The discrete symmetry that yields the Inert Doublet is unbroken, so that Dark Matter may be composed of neutral inert Higgs bosons, which may have escaped detection at LEP2. Predictions are given for multilepton events with missing transverse energy at the Large Hadron Collider, and for the direct detection of dark matter.

The successful prediction of the weak mixing angle suggests that the effective theory beneath the grand unification scale is the minimal supersymmetric standard model (MSSM) with just two Higgs doublets. If we further assume that the unified gauge group contains S0(10), that the two light Higgs doublets lie mostly in a single irreducible SO(10) representation, and that the t , b, and T masses originate in renormalizable Yukawa interactions of the form 1630163, then also the top quark mass can be predicted in terms of the MSSM parameters. To compute mt we present a precise analytic approximation to the solution of the two-loop renormalization group equations, and study supersymmetric and GUT threshold corrections and the input value of the b quark mass. The large ratio of top to bottom quark masses derives from a large ratio, tanp, Higgs vacuum expectation values. We point out that when tanp is large, so we certain corrections to the b quark mass prediction, unless a particular hierarchy exists in the parameters of the model. With such a hierarchy, which may result from approximate symmetries, the top mass prediction depends only weakly on the spectrum. Our results may be applied to any supersymmetric SO (10) model as long as At -X b N AT at the GUT scale and there are no intermediate mass scales in the desert. PACS number(s): 12.10.Dm, 12.15.Ff, 12.60.Jv, 14.65.Ha