118800400
Theory and Phenomenology of Dirac Leptogenesis
Dirac leptogenesis, in which neutrinos are purely Dirac and develop small but nonzero effective masses without the aid of the see-saw mechanism, provides an interesting alternative to the standard leptogenesis picture. Here we review the theory and phenomenology of Dirac leptogenesis and show that it is a viable theory capable of simultaneously satisfying all relevant bounds from cosmology, neutrino physics, and flavor violation. In addition, we also explore several potential extensions of the model, such as the possibility of right-handed sneutrino dark matter and the potential for relating the leptogenesis mechanism to the origin of the mu-term. Theories with a heavy gravitino and gaugino masses generated by anomaly mediation emerge as one natural context for Dirac leptogenesis. In such models the lightest neutralino is often expected to be predominately wino or Higgsino, and is a viable dark matter candidate. We conclude with an examination of the prospects for detecting the effectively monoenergetic photon signal that results from the annihilation of such a dark matter particle in the galactic halo.
18588087
Lepton flavor violation and supersymmetric Dirac leptogenesis
Dirac leptogenesis (or Dirac neutrinogenesis), in which neutrinos are purely Dirac particles, is an interesting alternative to the standard leptogenesis scenario. In its supersymmetric version, the modified form of the superpotential required for successful baryogenesis contributes new, generically nonflavor-diagonal terms to the slepton and sneutrino mass matrices. In this work, we examine how current experimental bounds on flavor-changing effects in the lepton sector (and particularly the bound on {mu}{yields}e{gamma}) constrain Dirac leptogenesis and we find that it is capable of succeeding with superpartner masses as low as {approx}100 GeV. For such light scalars and electroweakinos, upcoming experiments such as MEG are generically expected to observe signals of lepton flavor violation.
118366475
Cascades and collapses, "great walls" and "forbidden cities": Infinite towers of metastable vacua in supersymmetric field theories
We present a series of supersymmetric models exhibiting an entirely new vacuum structure: towers of metastable vacua with higher and higher energies. As the number of vacua grows towards infinity, the energy of the highest vacuum remains fixed while the energy of the true ground state tends towards zero. We study the instanton-induced tunneling dynamics associated with such vacuum towers and find that many distinct decay patterns along the tower are possible: these include not only regions of vacua experiencing direct collapses and/or tumbling cascades, but also other regions of vacua whose stability is protected by 'great walls' as well as regions of vacua populating 'forbidden cities' into which tunneling cannot occur. We also discuss possible applications of this setup for the cosmological-constant problem, for studies of the string landscape, for supersymmetry breaking, and for Z{sup '} phenomenology. Finally, we point out that a limiting case of our setup yields theories with yet another new vacuum structure: infinite numbers of degenerate vacua. As a result, the true ground states of such theories are Bloch waves, with energy eigenvalues approximating a continuum and giving rise to a vacuum 'band' structure.
120591006
Dynamical dark matter: A new framework for dark-matter physics
Although much remains unknown about the dark matter of the universe, one property is normally considered sacrosanct: dark matter must be stable well beyond cosmological time scales. However, a new framework for dark-matter physics has recently been proposed which challenges this assumption. In the "dynamical dark matter" (DDM) framework, the dark sector consists of a vast ensemble of individual dark-matter components with differing masses, lifetimes, and cosmological abundances. Moreover, the usual requirement of stability is replaced by a delicate balancing between lifetimes and cosmological abundances across the ensemble as a whole. As a result, it is possible for the DDM ensemble to remain consistent with all experimental and observational bounds on dark matter while nevertheless giving rise to collective behaviors which transcend those normally associated with traditional dark-matter candidates. These include a new, non-trivial darkmatter equation of state as well as potentially distinctive signatures...
24171176
Dark-matter decay as a complementary probe of multicomponent dark sectors.
In single-component theories of dark matter, the 2→2 amplitudes for dark-matter production, annihilation, and scattering can be related to each other through various crossing symmetries. The detection techniques based on these processes are thus complementary. However, multicomponent theories exhibit an additional direction for dark-matter complementarity: the possibility of dark-matter decay from heavier to lighter components. We discuss how this new detection channel may be correlated with the others, and demonstrate that the enhanced complementarity which emerges can be an important ingredient in probing and constraining the parameter spaces of such models.
119103684
Phenomenology of dirac neutrinogenesis in split supersymmetry
In split-supersymmetry scenarios the possibility of having a very heavy gravitino opens the door to alleviate or completely solve the worrisome ``gravitino problem'' in the context of supersymmetric baryogenesis models. Here we assume that the gravitino may indeed be heavy and that Majorana masses for neutrinos are forbidden as well as direct Higgs Yukawa couplings between left- and right-handed neutrinos. We investigate the viability of the mechansim known as Dirac leptogenesis (or neutrinogenesis), both in solving the baryogenesis puzzle and explaining the observed neutrino sector phenomenology. To successfully address these issues, the scenario requires the introduction of at least two new heavy fields. If a hierarchy among these new fields is introduced, and some reasonable stipulations are made on the couplings that appear in the superpotential, it becomes a generic feature to obtain the observed large lepton mixing angles. We show that in this case, it is possible simultaneously to obtain both the correct neutrino phenomenology and enough baryon number, making thermal Dirac neutrinogenesis viable. However, due to cosmological constraints, its ability to satisfy these constraints depends nontrivially on model parameters of the overall theory, particularly the gravitino mass. Split supersymmetry with ${10}^{5}\text{ }\text{ }\mathrm{GeV}\ensuremath{\lesssim}{m}_{3/2}\ensuremath{\lesssim}{10}^{10}\text{ }\text{ }\mathrm{GeV}$ emerges as a ``natural habitat'' for thermal Dirac neutrinogenesis.
125893696
Dynamical Dark Matter: Introduction, Equation of State, and Cosmological Implications