9,900 research outputs found
TeV resonances in top physics at the LHC
We consider the possibility of studying novel particles at the TeV scale with
enhanced couplings to the top quark via top quark pair production at the LHC
and VLHC. In particular we discuss the case of neutral scalar and vector
resonances associated with a strongly interacting electroweak symmetry breaking
sector. We constrain the couplings of these resonances by imposing appropriate
partial wave unitarity conditions and known low energy constraints. We evaluate
the new physics signals via WW -> tt~ for various models without making
approximation for the initial state W bosons, and optimize the acceptance cuts
for the signal observation. We conclude that QCD backgrounds overwhelm the
signals in both the LHC and a 200 TeV VLHC, making it impossible to study this
type of physics in the tt~ channel at those machines.Comment: 15p, add. comments to clarify model, +2 ref., version to appear PR
K+ -> pi+ nu nu(bar) and FCNC from non-universal Z' bosons
Motivated by the E787 and E949 result for K+ -> pi+ nu nu(bar) we examine the
effects of a new non-universal right-handed Z' boson on flavor changing
processes. We place bounds on the tree-level FCNC from K-K(bar) and B-B(bar)
mixing as well as from the observed CP violation in kaon decay. We discuss the
implications for K -> pi nu nu(bar), B -> X nu nu(bar) and B -> tau+ tau-. We
find that existing bounds allow substantial enhancements in the K+ -> pi+ nu
nu(bar) rate, particularly through a new one-loop Z' penguin operator.Comment: Typos corrected, references added, version to appear in PR
Charge-density waves in one-dimensional Hubbard superlattices
We study the formation of charge density waves (CDW's) in one-dimensional
Hubbard superlattices, modeled by a repeated pattern of repulsive (U>0) and
free (U=0) sites. By means of Lanczos diagonalizations for the ground state, we
calculate the charge structure factor. Our results show that while the
superlattice structure affects the modulation of the charge density waves, the
periodicity can still be predicted through an effective density. We also show
that, for a fixed repulsive layer thickness, the periodicity of the CDW is an
oscillatory function of the free layer thickness.Comment: 4 pages, 4 figure
Shaping the waveform of entangled photons
We demonstrate experimentally the tunable control of the joint spectrum, i.e.
waveform and degree of frequency correlations, of paired photons generated in
spontaneous parametric downconversion. This control is mediated by the spatial
shape of the pump beam in a type-I noncollinear configuration. We discuss the
applicability of this technique to other sources of frequency entangled
photons, such as electromagnetically induced Raman transitions.Comment: 5 Pages, 4 Figure
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