12,252 research outputs found
Neutral kaon mixing beyond the standard model with nf=2+1 chiral fermions
We compute the hadronic matrix elements of the four-quark operators needed
for the study of neutral kaon mixing beyond the Standard Model (SM). We use
nf=2+1 flavours of domain-wall fermions (DWF) which exhibit good chiral-flavour
symmetry. The renormalization is performed non-perturbatively through the
RI-MOM scheme and our results are converted perturbatively to MSbar. The
computation is performed on a single lattice spacing a=0.086 fm with a lightest
unitary pion mass of 290 MeV. The various systematic errors, including the
discretisation effects, are estimated and discussed. Our results confirm a
previous quenched study, where large ratios of non-SM to SM matrix elements
were obtained.Comment: 5 pages, 4 figures, 1 table. v2 paper version, R3 and B3 corrected,
conversion to 2GeV added, references adde
An AdS/QCD holographic wavefunction for the rho meson and diffractive rho meson electroproduction
We show that AdS/QCD generates predictions for the rate of diffractive rho
meson electroproduction that are in agreement with data collected at the HERA
electron-proton collider.Comment: 9 pages, 4 figures. Figure 3 added to illustrate that the AdS/QCD
prediction is impressive. Accepted for publication in Physical Review Letter
Do Quasars Lens Quasars?
If the unexpectedly high frequency of quasar pairs with very different
component redshifts is due to the lensing of a population of background quasars
by the foreground quasar, typical lens masses must be \sim10^{12}M_{\sun} and
the sum of all such quasar lenses would have to contain times the
closure density of the Universe. It then seems plausible that a very high
fraction of all \sim10^{12} M_{\sun} gravitational lenses with redshifts
contain quasars. Here I propose that these systems have evolved to
form the present population of massive galaxies with M and M
>5\times10^{11} M_{\sun}.Comment: 6 pages, aas style, ams symbols, ApJL (accepted
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