751 research outputs found
Electroweak non-resonant corrections to top pair production close to threshold
The production of W+ W- b bbar from e+ e- collisions at energies close to the
t tbar threshold is dominated by the resonant process with a nearly on-shell t
tbar intermediate state. The W b pairs in the final state can also be reached
through the decay of off-shell tops or through background processes containing
no or only single top quarks. This non-resonant production starts to contribute
at NLO to the W+ W- b bbar total cross section in the non-relativistic
power-counting v ~ alpha_s ~ sqrt(alpha_EW). The NLO non-resonant corrections
presented in this talk represent the non-trivial NLO electroweak corrections to
the e+ e- -> W+ W- b bbar cross section in the top anti-top resonance region.
In contrast to the QCD corrections which have been calculated (almost) up to
NNNLO, the parametrically larger NLO electroweak contributions have not been
completely known so far, but are mandatory for the required accuracy at a
future linear collider. We consider the total cross section of the e+ e- -> W+
W- b bbar process and additionally implement cuts on the invariant masses of
the W+ b and W- bbar pairs.Comment: Talk presented at the 35th International Conference of High Energy
Physics - ICHEP2010, July 22-28, 2010, Paris France. 4 pages, 2 figure
Harmonic Analysis of Linear Fields on the Nilgeometric Cosmological Model
To analyze linear field equations on a locally homogeneous spacetime by means
of separation of variables, it is necessary to set up appropriate harmonics
according to its symmetry group. In this paper, the harmonics are presented for
a spatially compactified Bianchi II cosmological model -- the nilgeometric
model. Based on the group structure of the Bianchi II group (also known as the
Heisenberg group) and the compactified spatial topology, the irreducible
differential regular representations and the multiplicity of each irreducible
representation, as well as the explicit form of the harmonics are all
completely determined. They are also extended to vector harmonics. It is
demonstrated that the Klein-Gordon and Maxwell equations actually reduce to
systems of ODEs, with an asymptotic solution for a special case.Comment: 28 pages, no figures, revised version to appear in JM
Electroweak Sudakov Logarithms and Real Gauge-Boson Radiation in the TeV Region
Electroweak radiative corrections give rise to large negative,
double-logarithmically enhanced corrections in the TeV region. These are partly
compensated by real radiation and, moreover, affected by selecting
isospin-noninvariant external states. We investigate the impact of real gauge
boson radiation more quantitatively by considering different restricted final
state configurations. We consider successively a massive abelian gauge theory,
a spontaneously broken SU(2) theory and the electroweak Standard Model. We find
that details of the choice of the phase space cuts, in particular whether a
fraction of collinear and soft radiation is included, have a strong impact on
the relative amount of real and virtual corrections.Comment: 20 pages, 4 figure
On Languages Accepted by P/T Systems Composed of joins
Recently, some studies linked the computational power of abstract computing
systems based on multiset rewriting to models of Petri nets and the computation
power of these nets to their topology. In turn, the computational power of
these abstract computing devices can be understood by just looking at their
topology, that is, information flow.
Here we continue this line of research introducing J languages and proving
that they can be accepted by place/transition systems whose underlying net is
composed only of joins. Moreover, we investigate how J languages relate to
other families of formal languages. In particular, we show that every J
language can be accepted by a log n space-bounded non-deterministic Turing
machine with a one-way read-only input. We also show that every J language has
a semilinear Parikh map and that J languages and context-free languages (CFLs)
are incomparable
Quantum state transfer in a q-deformed chain
We investigate the quantum state transfer in a chain of particles satisfying
q-deformed oscillators algebra. This general algebraic setting includes the
spin chain and the bosonic chain as limiting cases. We study conditions for
perfect state transfer depending on the number of sites and excitations on the
chain. They are formulated by means of irreducible representations of a quantum
algebra realized through Jordan-Schwinger maps. Playing with deformation
parameters, we can study the effects of nonlinear perturbations or interpolate
between the spin and bosonic chain.Comment: 13 pages, 4 figure
Electroweak Corrections using Effective Field Theory: Applications to the LHC
Electroweak Sudakov logarithms at high energy, of the form alpha/sin^2
theta_W^n log^m s/M_{Z,W}^2, are summed using effective theory (EFT) methods.
The exponentiation of Sudakov logarithms and factorization is discussed in the
EFT formalism. Radiative corrections are computed to scattering processes in
the standard model involving an arbitrary number of external particles. The
computations include non-zero particle masses such as the t-quark mass,
electroweak mixing effects which lead to unequal W and Z masses and a massless
photon, and Higgs corrections proportional to the top quark Yukawa coupling.
The structure of the radiative corrections, and which terms are summed by the
EFT renormalization group is discussed in detail. The omitted terms are smaller
than 1%. We give numerical results for the corrections to dijet production,
dilepton production, t-\bar t production, and squark pair production. The
purely electroweak corrections are significant -- about 15% at 1 TeV,
increasing to 30% at 5 TeV, and they change both the scattering rate and
angular distribution. The QCD corrections (which are well-known) are also
computed with the EFT. They are much larger -- about a factor of four at 1 TeV,
increasing to a factor of thirty at 5 TeV. Mass effects are also significant;
the q \bar q -> t \bar t rate is enchanced relative to the light-quark
production rate by 40%.Comment: Additional details added on exponentiation, and the form of the
Sudakov series. Figures darkened to print better. 40 pages, 40 figure
Electrocardiogram of the Mixmaster Universe
The Mixmaster dynamics is revisited in a new light as revealing a series of
transitions in the complex scale invariant scalar invariant of the Weyl
curvature tensor best represented by the speciality index , which
gives a 4-dimensional measure of the evolution of the spacetime independent of
all the 3-dimensional gauge-dependent variables except for the time used to
parametrize it. Its graph versus time characterized by correlated isolated
pulses in its real and imaginary parts corresponding to curvature wall
collisions serves as a sort of electrocardiogram of the Mixmaster universe,
with each such pulse pair arising from a single circuit or ``complex pulse''
around the origin in the complex plane. These pulses in the speciality index
and their limiting points on the real axis seem to invariantly characterize
some of the so called spike solutions in inhomogeneous cosmology and should
play an important role as a gauge invariant lens through which to view current
investigations of inhomogeneous Mixmaster dynamics.Comment: version 3: 20 pages iopart style, 19 eps figure files for 8 latex
figures; added example of a transient true spike to contrast with the
permanent true spike example from the Lim family of true spike solutions;
remarks in introduction and conclusion adjusted and toned down; minor
adjustments to the remaining tex
Covariant Calculation of General Relativistic Effects in an Orbiting Gyroscope Experiment
We carry out a covariant calculation of the measurable relativistic effects
in an orbiting gyroscope experiment. The experiment, currently known as Gravity
Probe B, compares the spin directions of an array of spinning gyroscopes with
the optical axis of a telescope, all housed in a spacecraft that rolls about
the optical axis. The spacecraft is steered so that the telescope always points
toward a known guide star. We calculate the variation in the spin directions
relative to readout loops rigidly fixed in the spacecraft, and express the
variations in terms of quantities that can be measured, to sufficient accuracy,
using an Earth-centered coordinate system. The measurable effects include the
aberration of starlight, the geodetic precession caused by space curvature, the
frame-dragging effect caused by the rotation of the Earth and the deflection of
light by the Sun.Comment: 7 pages, 1 figure, to be submitted to Phys. Rev.
On unitarizability in the case of classical p-adic groups
In the introduction of this paper we discuss a possible approach to the
unitarizability problem for classical p-adic groups. In this paper we give some
very limited support that such approach is not without chance. In a forthcoming
paper we shall give additional evidence in generalized cuspidal rank (up to)
three.Comment: This paper is a merged and revised version of ealier preprints
arXiv:1701.07658 and arXiv:1701.07662. The paper is going to appear in the
Proceedings of the Simons Symposium on Geometric Aspects of the Trace Formul
- …