2,463 research outputs found
Ultrasoft contribution to heavy-quark pair production near threshold
We compute the third-order correction to the heavy-quark current correlation
function due to the emission and absorption of an ultrasoft gluon. Our result
supplies a missing contribution to top-quark pair production near threshold and
the determination of the bottom quark mass from QCD sum rules.Comment: 10 pages, LaTe
New global stability estimates for monochromatic inverse acoustic scattering
We give new global stability estimates for monochromatic inverse acoustic
scattering. These estimates essentially improve estimates of [P. Hahner, T.
Hohage, SIAM J. Math. Anal., 33(3), 2001, 670-685] and can be considered as a
solution of an open problem formulated in the aforementioned work
Semileptonic Meson Decays Into A Highly Excited Charmed Meson Doublet
We study the heavy quark effective theory prediction for semileptonic
decays into an orbital excited -wave charmed doublet, the (, )
states (, ), at the leading order of heavy quark expansion.
The corresponding universal form factor is estimated by using the QCD sum rule
method. The decay rates we predict are and . The branching ratios are
and
, respectively.Comment: 6 pages,2 figure
The Hopf Skyrmion in QCD with Adjoint Quarks
We consider a modification of QCD in which conventional fundamental quarks
are replaced by Weyl fermions in the adjoint representation of the color SU(N).
In the case of two flavors the low-energy chiral Lagrangian is that of the
Skyrme-Faddeev model. The latter supports topologically stable solitons with
mass scaling as N^2. Topological stability is due to the existence of a
nontrivial Hopf invariant in the Skyrme-Faddeev model. Our task is to identify,
at the level of the fundamental theory, adjoint QCD, an underlying reason
responsible for the stability of the corresponding hadrons. We argue that all
"normal" mesons and baryons, with mass O(N^0), are characterized by (-1)^Q
(-1)^F =1, where Q is a conserved charge corresponding to the unbroken U(1)
surviving in the process of the chiral symmetry breaking (SU(2) \to U(1) for
two adjoint flavors). Moreover, F is the fermion number (defined mod 2 in the
case at hand). We argue that there exist exotic hadrons with mass O(N^2) and
(-1)^Q (-1)^F = -1. They are in one-to-one correspondence with the Hopf
Skyrmions. The transition from nonexotic to exotic hadrons is due to a shift in
F, namely F \to F - {\cal H} where {\cal H} is the Hopf invariant. To detect
this phenomenon we have to extend the Skyrme-Faddeev model by introducing
fermions.Comment: 18 pages, 3 figures; v.2: a reference and a comment added; v.3: two
comments added, figures improve
Efficiency at maximum power of thermally coupled heat engines
We study the efficiency at maximum power of two coupled heat engines, using
thermoelectric generators (TEGs) as engines. Assuming that the heat and
electric charge fluxes in the TEGs are strongly coupled, we simulate
numerically the dependence of the behavior of the global system on the
electrical load resistance of each generator in order to obtain the working
condition that permits maximization of the output power. It turns out that this
condition is not unique. We derive a simple analytic expression giving the
relation between the electrical load resistance of each generator permitting
output power maximization. We then focuse on the efficiency at maximum power
(EMP) of the whole system to demonstrate that the Curzon-Ahlborn efficiency may
not always be recovered: the EMP varies with the specific working conditions of
each generator but remains in the range predicted by irreversible
thermodynamics theory. We finally discuss our results in light of non-ideal
Carnot engine behavior.Comment: 11 pages, 7 figure
The New Fat Higgs: Slimmer and More Attractive
In this paper we increase the MSSM tree level higgs mass bound to a value
that is naturally larger than the LEP-II search constraint by adding to the
superpotential a term, as in the NMSSM, and UV
completing with new strong dynamics {\it before} becomes
non-perturbative. Unlike other models of this type the higgs fields remain
elementary, alleviating the supersymmetric fine-tuning problem while
maintaining unification in a natural way.Comment: 14 pages and 2 figures. Added references and updated argument about
constraints from reheating temperatur
Ultrasoft contribution to quarkonium production and annihilation
We compute the third-order correction to electromagnetic
S-wave quarkonium production and annihilation rates due to the emission and
absorption of an ultrasoft gluon. Our result completes the analysis of the
non-relativistic quarkonium bound-state dynamics in the
next-to-next-to-next-to-leading order. The impact of the ultrasoft correction
on the Upsilon(1S) leptonic width and the top quark-antiquark threshold
production cross section is estimated.Comment: 10 page
Are physical objects necessarily burnt up by the blue sheet inside a black hole?
The electromagnetic radiation that falls into a Reissner-Nordstrom black hole
develops a ``blue sheet'' of infinite energy density at the Cauchy horizon. We
consider classical electromagnetic fields (that were produced during the
collapse and then backscattered into the black hole), and investigate the
blue-sheet effects of these fields on infalling objects within a simplified
model. These effects are found to be finite and even negligible for typical
parameters.Comment: 13 pages, ordinary LaTex. Accepted for Physical Review Letters
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