Search

There has been a steady interest in flavor anomalies and their global fits as ideal probes of new physics. If the anomalies are real, one promising explanation is a new Z ′ gauge boson with a flavor-changing coupling to bottom and strange quarks and a flavor-conserving coupling to muons and, possibly, electrons. We point out that direct production of such a Z ′ , emerging from the collision of b and s quarks, may offer a complementary window into these phenomena because collider searches already provide competitive constraints. On top of that, we analyze the same Z ′ scenario in relation to another long-standing discrepancy between theory and experiment that concerns the anomalous magnetic moment of the muon. By scanning the allowed Z ′ coupling strengths in the low-mass region, we assess the compatibility of the signals from LHCb with the Z ′ searches in the high energy LHC data and the measurements of the anomalous magnetic moments of the involved leptons. We also argue that observations of the latter can break the degeneracy pattern in the Wilson coefficients C 9 and C 10 presented by LHCb data. The Z ′ model we consider is compatible with the new measurement of R K ⁎ , therefore it can potentially account for the long-standing deviations observed in B -physics. [ABSTRACT FROM AUTHOR]

Abstract: We extend the results of Sannino (2010) by computing the S-parameter at two loops in the perturbative region of the conformal window. Consistently using the expression for the location of the infrared fixed point at the two-loop order we express the S-parameter in terms of the number of flavors, colors and matter representation. We show that S, normalized to the number of flavors, increases as we decrease the number of flavors. Our findings support the conjecture presented in Sannino (2010) according to which the normalized value of the S-parameter at the upper end of the conformal window constitutes the lower bound across the entire phase diagram for the given underlying asymptotically free gauge theory. We also show that the non-trivial dependence on the number of flavors merges naturally with the non-perturbative estimate of the S-parameter close to the lower end of the conformal window obtained using gauge duality (Sannino, 2010) . Our results are natural benchmarks for lattice computations of the S-parameter for vector-like gauge theories. [Copyright &y& Elsevier]

We introduce a toy model implementing the proposal of using a custodial symmetry to protect the $Zb_L \bar{b}_L$ coupling from large corrections. This "doublet-extended standard model" adds a weak doublet of fermions (including a heavy partner of the top quark) to the particle content of the standard model in order to implement an O(4) × U(1)X ~ SU(2)L × SU(2)R × PLR × U(1)X symmetry in the top-quark mass generating sector. This symmetry is softly broken to the gauged SU(2)L × U(1)Y electroweak symmetry by a Dirac mass M for the new doublet; adjusting the value of M allows us to explore the range of possibilities between the O(4)-symmetric (M → 0) and standard-model-like (M → ∞) limits. [ABSTRACT FROM AUTHOR]