6,861 research outputs found
Z-Z' Mixing and Z-Mediated FCNCs in SU(3)_C x SU(3)_L x U(1)_X Models
Most of the existing analyses of FCNC processes in the 331 models, based on
the gauge group SU(3)_C x SU(3)_L x U(1)_X, take only into account tree-level
exchanges of a new heavy neutral gauge boson Z'. However due to the Z-Z' mixing
also corresponding contributions from Z boson are present that are usually
neglected. We calculate the impact of these contributions on Delta F=2
processes and rare K, B_s and B_d decays for different values of a parameter
beta, which distinguishes between various 331 models and for different fermion
representations under the SU(3)_L group. We find a general expression for the
Z-Z' mixing in terms beta, M_Z, M_Z' and tan(bar{beta}), familiar from 2 Higgs
Doublet models, that differs from the one quoted in the literature. We study in
particular the models with beta=+-n/sqrt{3} with n=1,2 which have recently been
investigated by us in the context of new data on B_{s,d}->mu^+ mu^- and
B_d->K^*(K)mu^+ mu^-. We find that these new contributions can indeed be
neglected in the case of Delta F=2 transitions and decays, like
B_d->K^*mu^+mu^-, where they are suppressed by the small vectorial Z coupling
to charged leptons. However the contributions of tree-level Z exchanges to
decays sensitive to axial-vector couplings, like B_{s,d}->mu^+ mu^- and B_d->K
mu^+ mu^-, and those with neutrinos in the final state, like b->s nu bar{nu}
transitions, K^+->pi^+ nu bar{nu} and K_L->pi^0 nu bar{nu} cannot be generally
neglected with size of Z contributions depending on beta, tan(bar{beta}) and
M_Z'. We analyze for the first time the ratio epsilon'/epsilon in these models
including both Z' and Z contributions. Our analysis of electroweak precision
observables within 331 models demonstrates transparently that the interplay of
NP effects in electroweak precision observables and those in flavour
observables could allow in the future to identify the favourite 331 model.Comment: 44 pages, 15 figures, 9 tables; clarifying comments added; version
accepted for publication in JHE
Quench dynamics of a disordered array of dissipative coupled cavities
We investigate the mean-field dynamics of a system of interacting photons in
an array of coupled cavities in presence of dissipation and disorder. We follow
the evolution of on an initially prepared Fock state, and show how the
interplay between dissipation and disorder affects the coherence properties of
the cavity emission and that these properties can be used as signatures of the
many-body phase of the whole array.Comment: 8 pages, 10 figures, new reference adde
Anomalous density of states of a Luttinger liquid in contact with a superconductor
We study the frequency and space dependence of the local tunneling density of
states of a Luttinger liquid (LL) which is connected to a superconductor. This
coupling {\em strongly} modifies the single-particle properties of the LL. It
significantly enhances the density of states near the Fermi level, whereas this
quantity vanishes as a power law for an isolated LL. The enhancement is due to
the interplay between electron-electron interactions and multiple
back-scattering processes of low-energy electrons at the interface between the
LL and the superconductor. This anomalous behavior extends over large distances
from the interface and may be detected by coupling normal probes to the system.Comment: 8 pages Revtex, two postscript figure
Non-abelian superconducting pumps
Cooper pair pumping is a coherent process. We derive a general expression for
the adiabatic pumped charge in superconducting nanocircuits in the presence of
level degeneracy and relate it to non-Abelian holonomies of Wilczek and Zee. We
discuss an experimental system where the non-Abelian structure of the adiabatic
evolution manifests in the pumped charge.Comment: 5 pages, 3 figure
Generalised Unitarity for Dimensionally Regulated Amplitudes
We present a novel set of Feynman rules and generalised unitarity
cut-conditions for computing one-loop amplitudes via d-dimensional integrand
reduction algorithm. Our algorithm is suited for analytic as well as numerical
result, because all ingredients turn out to have a four-dimensional
representation. We will apply this formalism to NLO QCD corrections.Comment: Presented at SILAFAE 2014, 24-28 Nov, Ruta N, Medellin, Colombi
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