10,434 research outputs found
Ground-state of graphene in the presence of random charged impurities
We calculate the carrier density dependent ground state properties of
graphene in the presence of random charged impurities in the substrate taking
into account disorder and interaction effects non-perturbatively on an equal
footing in a self-consistent theoretical formalism. We provide detailed
quantitative results on the dependence of the disorder-induced spatially
inhomogeneous two-dimensional carrier density distribution on the external gate
bias, the impurity density, and the impurity location. We find that the
interplay between disorder and interaction is strong, particularly at lower
impurity densities. We show that for the currently available typical graphene
samples, inhomogeneity dominates graphene physics at low (
cm) carrier density with the density fluctuations becoming larger than
the average density.Comment: Final version, accepted for publication in Phys. Rev. Let
Spontaneous interlayer superfluidity in bilayer systems of cold polar molecules
Quantum degenerate cold-atom gases provide a remarkable opportunity to study
strongly interacting systems. Recent experimental progress in producing
ultracold polar molecules with a net electric dipole moment opens up new
possibilities to realize novel quantum phases governed by the long-range and
anisotropic dipole-dipole interactions. In this work we predict the existence
of experimentally observable novel broken-symmetry states with spontaneous
interlayer coherence in cold polar molecules. These exotic states appear due to
strong repulsive interlayer interactions and exhibit properties of superfluids,
ferromagnets and excitonic condensates.Comment: 7 pages, 5 figures, final versio
Effects of an extra U(1) axial condensate on the strong decays of pseudoscalar mesons
We consider a scenario (supported by some lattice results) in which a
U(1)-breaking condensate survives across the chiral transition in QCD. This
scenario has important consequences for the pseudoscalar-meson sector, which
can be studied using an effective Lagrangian model. In particular, generalizing
the results obtained in two previous papers, where the effects on the radiative
decays eta,eta' --> gamma gamma were studied, in this paper we study the
effects of the U(1) chiral condensate on the strong decays of the "light"
pseudoscalar mesons, i.e., eta,eta' --> 3pi^0; eta,eta' --> pi^+ pi^- pi^0;
eta' --> eta pi^0 pi^0; eta' --> eta pi^+ pi^-; and also on the strong decays
of an exotic ("heavy") SU(3)-singlet pseudoscalar state eta_X, predicted by the
model.Comment: One misprint in Eq. (2.10) has been eliminated; Eqs. (B.8) and (B.9)
in Appendix B have been corrected; 46 pages, 1 tabl
Lattice QCD inputs to the CKM unitarity triangle analysis
We perform a global fit to the CKM unitarity triangle using the latest
experimental and theoretical constraints. Our emphasis is on the hadronic weak
matrix elements that enter the analysis, which must be computed using lattice
QCD or other nonperturbative methods. Realistic lattice QCD calculations which
include the effects of the dynamical up, down, and strange quarks are now
available for all of the standard inputs to the global fit. We therefore
present lattice averages for all of the necessary hadronic weak matrix
elements. We attempt to account for correlations between lattice QCD results in
a reasonable but conservative manner: whenever there are reasons to believe
that an error is correlated between two lattice calculations, we take the
degree of correlation to be 100%. These averages are suitable for use as inputs
both in the global CKM unitarity triangle fit and other phenomenological
analyses. In order to illustrate the impact of the lattice averages, we make
Standard Model predictions for the parameters BK, |Vcb|, and |Vub|/|Vcb|. We
find a (2-3) sigma tension in the unitarity triangle, depending upon whether we
use the inclusive or exclusive determination of |Vcb|. If we interpret the
tension as a sign of new physics in either neutral kaon or B mixing, we find
that the scenario with new physics in kaon-mixing is preferred by present data.Comment: 33 pages, 12 figures, references added, discussion slightly expanded,
updated values of alpha, Vcb inclusive, and Vub inclusiv
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