Cogenesis in a universe with vanishing B−LB-L within a gauged U(1)xU(1)_x extension

We consider a gauged $U(1)_x$ extension of the standard model and of the minimal supersymmetric standard model where the dark matter fields are charged under $U(1)_x$ and carry lepton number while the standard model fields and fields of the minimal supersymmetric standard model are neutral under $U(1)_x$. We consider leptogenesis in this class of models with all fundamental interactions having no violation of lepton number, and the total $B-L$ in the universe vanishes. Such leptogenesis leads to equal and opposite lepton numbers in the visible sector and in the dark sector, and thus also produces asymmetric dark matter. Part of the lepton numbers generated in the leptonic sector subsequently transfer to the baryonic sector via sphaleron interactions. The stability of the dark particles is protected by the $U(1)_x$ gauge symmetry. A kinetic mixing between the $U(1)_x$ and the $U(1)_Y$ gauge bosons allows for dissipation of the symmetric component of dark matter. The case when $U(1)_x$ is $U(1)_{B-L}$ is also discussed for the supersymmetric case. This case is particularly interesting in that we have a gauged $U(1)_{B-L}$ which ensures the conservation of $B-L$ with an initial condition of a vanishing $B-L$ in the universe. Phenomenological implications of the proposed extensions are discussed, which include implications for electroweak physics, neutrino masses and mixings, and lepton flavor changing processes such as $\ell_i \to \ell_j \gamma$. We also briefly discuss the direct detection of the dark matter in the model.Comment: 9 pages, 3 figure

Stringy explanation of b→sℓ+ℓ−b \to s \ell^+ \ell^- anomalies

We show that the recent anomalies in $b \to s \ell^+ \ell^-$ transitions observed by the LHCb collaboration can be accommodated within string motivated models with a low mass $Z^{\prime}$ gauge boson. Such $Z^{\prime}$ gauge boson can be obtained in compactifications with a low string scale. We consider a class of intersecting D-brane models, in which different families of quarks and leptons are simultaneously realized at different D-brane intersections. The explanation of $b \to s \ell^+ \ell^-$ anomalies via a stringy $Z^{\prime}$ sets important restrictions on these viable D-brane constructions.Comment: 18 pages, 13 figure

Massive Supermultiplets in Four-Dimensional Superstring Theory

We extend the discussion of arXiv:1007.5254 on massive Regge excitations on the first mass level of four-dimensional superstring theory. For the lightest massive modes of the open string sector, universal supermultiplets common to all four-dimensional compactifications with N = 1, 2 and N = 4 spacetime supersymmetry are constructed respectively -- both their vertex operators and their supersymmetry variations. Massive spinor helicity methods shed light on the interplay between individual polarization states.Comment: 75 pages, 13 figure

Building a St\"uckelberg Portal

We construct explicit string theory models realizing the recently proposed "St\"uckelberg Portal" scenario, a framework for building Z' mediation models without the need to introduce unwanted exotic matter charged under the Standard Model. This scenario can be viewed purely field-theoretically, although it is particularly well motivated from string theory. By analyzing carefully the St\"uckelberg couplings between the Abelian gauge bosons and the RR axions, we construct the first global intersecting brane models which extend the Standard Model with a genuine hidden sector, to which it is nonetheless connected via U(1) mass mixings. Utilizing the explicit models we construct, we discuss some broad phenomenological properties and experimental implications of this scenario such as Z-Z' mixings, dark matter stability and relic density, and supersymmetry mediation. With an appropriate confining hidden sector, our setup also provides a minimal realization of the hidden valley scenario. We further explore the possibility of obtaining small Z' masses from a large ensemble of U(1) bosons. Related to the St\"uckelberg portal are two mechanisms that connect the visible and the hidden sectors, namely mediation by non-perturbative operators and the hidden photon scenario, on which we briefly comment.Comment: 39 pages, 11 figure