Z' Physics and Supersymmetry

We review the status of heavy neutral gauge bosons, Z', with emphasis on constraints that arise in supersymmetric models, especially those motivated from superstring compactifications. We first summarize the current phenomenological constraints and the prospects for Z' detection and diagnostics at the LHC and NLC. After elaborating on the status and (lack of) predictive power for general models with an additional Z', we concentrate on motivations and successes for Z' physics in supersymmetric theories in general and in a class of superstring models in particular. We review phenomenologically viable scenarios with the Z' mass in the electroweak or in the intermediate scale region.Comment: 30 pages. To appear in Perspectives in Supersymmetry, World Scientific, ed. G. L. Kan

B Decays in an Asymmetric Left-Right Model

Motivated by recently observed disagreements with the SM predictions in $B$ decays, we study $b \to d, s$ transitions in an asymmetric class of $SU(2)_L \times SU(2)_R \times U(1)_{B-L}$ models, with a simple one-parameter structure of the right handed mixing matrix for the quarks, which obeys the constraints from kaon physics. We use experimental constraints on the branching ratios of $b \to s \gamma$, $b \to c e {\bar \nu}_e$, and $B_{d,s}^0 -\bar{B}^0_{d,s}$ mixing to restrict the parameters of the model: $\displaystyle {g_R}/{g_L}, M_{W_2}, M_{H^\pm}, \tan \beta$ as well as the elements of the right-handed quark mixing matrix $V^R_{CKM}$. We present a comparison with the more commonly used (manifest) left-right symmetric model. Our analysis exposes the parameters most sensitive to $b$ transitions and reveals a large parameter space where left- and right-handed quarks mix differently, opening the possibility of observing marked differences in behaviour between the standard model and the left-right model.Comment: 32 pages and 8 figure

Constraints on the mass and mixing of Z' bosons

We tested several models in which the Standard Model (SM) gauge group is extended by an additional U(1) gauge symmetry, against available electroweak precision data to impose limits on the mass of the neutral Z' boson, M_Z', predicted in all such models, and on the Z-Z' mixing angle, theta_ZZ', at 95% C.L. We found lower limits on M_Z' of order 1 TeV in most cases, while theta_ZZ' was found to be constrained to very small values.Comment: Format fixed, 5 pages, 2 figures, Talk given at the 17th International Conference on Supersymmetry and the Unification of Fundamental Interactions (SUSY09), Boston, MA, USA, 5-10 June 2009, to be published in the conference proceedings (AIP

Blowing-Up the Four-Dimensional Z_3 Orientifold

We study the blowing-up of the four-dimensional Z_3 orientifold of Angelantonj, Bianchi, Pradisi, Sagnotti and Stanev (ABPSS) by giving nonzero vacuum expectation values (VEV's) to the twisted sector moduli blowing-up modes. The blowing-up procedure induces a Fayet-Iliopoulos (FI) term for the ``anomalous'' U(1), whose magnitude depends linearly on the VEV's of the blowing-up modes. To preserve the N=1 supersymmetry, non-Abelian matter fields are forced to acquire nonzero VEV's, thus breaking (some of) the non-Abelian gauge structure and decoupling some of the matter fields. We determine the form of the FI term, construct explicit examples of (non-Abelian) D and F flat directions, and determine the surviving gauge groups of the restabilized vacua. We also determine the mass spectra, for which the restabilization reduces the number of families.Comment: 19 pages, Late

Z' Searches: From Tevatron to LHC

The CDF collaboration has set lower limits on the masses of the Z' bosons occurring in a range of E_6 GUT based models. We revisit their analysis and extend it to certain other E_6 scenarios as well as to some general classes of models satisfying the anomaly cancellation conditions, which are not included in the CDF analysis. We also suggest a Bayesian statistical method for finding exclusion limits on the Z' mass, which allows one to explore a wide range of the U(1)' gauge coupling parameter. This method also takes into account the effects of interference between the Z' and the SM gauge bosons.Comment: 5 pages. Talk given at the XXIInd Rencontres de Blois, Loire, France, 16-20 July 201

Physics Implications of Precision Electroweak Experiments

A brief review is given of precision electroweak physics, and its implications for establishing the standard model and constraining the possibilities for new physics at the TeV scale and beyond