26,396 research outputs found
Minimal Lepton Flavor Violation Implications of the Anomalies
The latest measurements of rare decays in the LHCb experiment have
led to results in tension with the predictions of the standard model (SM),
including a tentative indication of the violation of lepton flavor
universality. Assuming that this situation will persist because of new physics,
we explore some of the potential consequences in the context of the SM extended
with the seesaw mechanism involving right-handed neutrinos plus effective
dimension-six lepton-quark operators under the framework of minimal flavor
violation. We focus on a couple of such operators which can accommodate the
LHCb anomalies and conform to the minimal flavor violation hypothesis in both
their lepton and quark parts. We examine specifically the
lepton-flavor-violating decays , ,
, and , as well as
and , induced by such operators. The estimated branching
fractions of some of these decay modes with in the final states are
allowed by the pertinent experimental constraints to reach a few times
if other operators do not yield competitive effects. We also look at
the implications for and , finding that
their rates can be a few times larger than their SM values. These results are
testable in future experiments.Comment: 16 pages, no figures, clarifying comments added, references updated,
matches journal versio
Scaling and diffusion of Dirac composite fermions
We study the effects of quenched disorder and a dissipative Coulomb interaction on an anyon gas in a periodic potential undergoing a quantum phase transition. We use a (2+1)−dimensional low-energy effective description that involves Nf=1 Dirac fermion coupled to a U(1) Chern-Simons gauge field at level (θ−1/2). When θ=1/2 the anyons are free Dirac fermions that exhibit an integer quantum Hall transition; when θ=1 the anyons are bosons undergoing a superconductor-insulator transition in the universality class of the three-dimensional XY model. Using the large Nf approximation we perform a renormalization-group analysis. We find the Coulomb interaction to be an irrelevant perturbation of the clean fixed point for any θ. The dissipative Coulomb interaction allows for two classes of IR stable fixed points in the presence of disorder: those with a finite nonzero Coulomb coupling and dynamical critical exponent z=1 and those with an effectively infinite Coulomb coupling and 1<z<2. At θ=1/2 the clean fixed point is stable to charge-conjugation preserving (random mass) disorder, while a line of diffusive fixed points is obtained when the product of charge-conjugation and time-reversal symmetries is preserved. At θ=1 we find a finite disorder fixed point with unbroken charge-conjugation symmetry whether or not the Coulomb interaction is present. Other cases result in runaway flows. We comment on the relation of our results to other theoretical studies and the relevancy to experiment
Running cosmological constant with observational tests
We investigate the running cosmological constant model with dark energy
linearly proportional to the Hubble parameter, , in which the CDM limit is recovered by taking .
We derive the linear perturbation equations of gravity under the
Friedmann-Lema\"itre-Robertson-Walker cosmology, and show the power spectra of
the CMB temperature and matter density distribution. By using the Markov chain
Monte Carlo method, we fit the model to the current observational data and find
that and for coupled to matter and radiation-matter, respectively,
along with constraints on other cosmological parameters.Comment: 12 pages, 5 figures, version accepted by PL
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