Electroweak breaking and theμproblem in supergravity models with an additional U(1)

Abstract

We consider electroweak symmetry breaking in supersymmetric models with an extra nonanomalous U͑1͒Ј gauge symmetry and an extra standard-model singlet scalar S. For appropriate charges the U͑1͒Ј forbids an elementary term, but an effective is generated by the VEV of S, leading to a natural solution to the problem. There are a variety of scenarios leading to acceptably small Z-ZЈ mixing and other phenomenological consequences, all of which involve some but not excessive fine-tuning. One class, driven by a large trilinear soft supersymmetry-breaking term, implies small mixing, a light ZЈ ͑e.g., 200 GeV͒, and an electroweak phase transition that may be first order at the tree level. In another class, with m S 2 Ͻ0 ͑radiative breaking͒, the typical scale of dimensional parameters, including M Z Ј and the effective , is ϳ1TeV, but the electroweak scale is smaller due to cancellations. We relate the soft supersymmetry-breaking parameters at the electroweak scale to those at the string scale, choosing Yukawa couplings as determined within a class of string models. We find that one does not obtain either scenario for universal soft supersymmetry-breaking mass parameters at the string scale and no exotic multiplets contributing to the renormalization group equations. However, either scenario is possible when the assumption of universal soft breaking is relaxed. Radiative breaking can also be generated by exotics, which are expected in most string models.

Search for gauge extensions of the MSSM at the LHC

“…In fact, the SUð2Þ L breaking effects that split them in mass turn out to be small so that~0 2 and~AE 1 have approximately the same mass [3,16]. Hence, in the MSSM the decay ofW 3 dominantly gives a dilepton signal.…”

“…The extra chiral fieldŜ extends (i) the MSSM Higgs sector via the additional Higgs field S, and (ii) the MSSM neutralino sector via the additional neutral fermionS [3]. The other source of deviation from the MSSM stems from the presence of the extra gauge boson and its superpartner.…”

“…The squarks of the first and second generations possess the following properties: (i) the mass and gauge eigenstates (especially for the scalar up and down quarks) are identical due to their exceedingly small Yukawa couplings, (ii) the flavor and the gauge eigenstates of the scalar up and down quarks are identical whereas the scalar strange quark might possesses significant flavor mixing with the scalar bottom quark, (iii) they do not exhibit any appreciable coupling to the Higgsinos but only to the gauginos, and (iv) they turn out to be the heaviest scalars of approximately the same mass, nearly mass degenerate with the gluino, in the minimal supergravity [3]. In the light of these features, these squarks provide a perfect playground for probing the gaugino sector (and hence the extended gauge structures) with a conservative number of SUSY parameters (no direct dependence on the parameter and trilinear couplings, and a weak dependence on tan via D-term contributions).…”

“…stops, turn out to weigh well below the ones in the first and second generations thanks to the counterbalancing effect of the rise in the squark mass due to the Yukawa couplings [3]. Because of these features, the third-generation squarks involve a larger set of SUSY parameters than the first-and second-generation ones, and therefore, they enable exploration of various parameters, like the trilinear couplings and the parameter, not possible with the first-and second-generation squarks.…”

LHC signatures of a Z ′ mediator between dark matter and the SU(3) sector

“…The B − L models are among the most popular example, and satisfy these requirements by considering a very heavy Z . On the other hand, string inspired models propose an anomaly cancellation a la Green-Schwarz [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] where a very light U(1) X mediator is generated with the use of axionic couplings and generalized ChernSimons terms, or via Stueckelberg realization of the Z boson [8,[42][43][44]. Another option is to consider neutral Standard Model fermions under the new gauge group U(1) X [11].…”