39 research outputs found
Frequency shifts in noble-gas magnetometers
Polarized nuclei are a powerful tool in nuclear spin studies and in searches
for beyond-the-standard model physics. Noble-gas comagnetometer systems, which
compare two nuclear species, have thus far been limited by anomalous frequency
variations of unknown origin. We studied the self-interactions in a
He-Xe system by independently addressing, controlling and measuring
the influence of each component of the nuclear spin polarization. Our results
directly rule out prior explanations of the shifts, and demonstrate
experimentally that they can be explained by species dependent
self-interactions. We also report the first gas phase frequency shift induced
by Xe on He.Comment: v.
Two-Loop Quark Self-Energy in a New Formalism (II): Renormalization of the Quark Propagator in the Light-Cone Gauge
The complete two-loop correction to the quark propagator, consisting of the
spider, rainbow, gluon bubble and quark bubble diagrams, is evaluated in the
noncovariant light-cone gauge (lcg). (The overlapping self-energy diagram had
already been computed.) The chief technical tools include the powerful matrix
integration technique, the n^*-prescription for the spurious poles of 1/qn, and
the detailed analysis of the boundary singularities in five- and
six-dimensional parameter space. It is shown that the total divergent
contribution to the two-loop correction Sigma_2 contains both covariant and
noncovariant components, and is a local function of the external momentum p,
even off the mass-shell, as all nonlocal divergent terms cancel exactly.
Consequently, both the quark mass and field renormalizations are local. The
structure of Sigma_2 implies a quark mass counterterm of the form ,
\tilde\alpha_s = g^2\Gamma(\eps)(4\pi)^{\eps -2}, with W depending only on
the dimensional regulator epsilon, and on the numbers of colors and flavors. It
turns out that \delta m(lcg) is identical to the mass counterterm in the
general linear covariant gauge. Our results are in agreement with the
Bassetto-Dalbosco-Soldati renormalization scheme.Comment: 36 pages Latex, 5 eps figures, to appear in Nucl.Phys.
Fast Evaluation of Feynman Diagrams
We develop a new representation for the integrals associated with Feynman
diagrams. This leads directly to a novel method for the numerical evaluation of
these integrals, which avoids the use of Monte Carlo techniques. Our approach
is based on based on the theory of generalized sinc () functions,
from which we derive an approximation to the propagator that is expressed as an
infinite sum. When the propagators in the Feynman integrals are replaced with
the approximate form all integrals over internal momenta and vertices are
converted into Gaussians, which can be evaluated analytically. Performing the
Gaussians yields a multi-dimensional infinite sum which approximates the
corresponding Feynman integral. The difference between the exact result and
this approximation is set by an adjustable parameter, and can be made
arbitrarily small. We discuss the extraction of regularization independent
quantities and demonstrate, both in theory and practice, that these sums can be
evaluated quickly, even for third or fourth order diagrams. Lastly, we survey
strategies for numerically evaluating the multi-dimensional sums. We illustrate
the method with specific examples, including the the second order sunset
diagram from quartic scalar field theory, and several higher-order diagrams. In
this initial paper we focus upon scalar field theories in Euclidean spacetime,
but expect that this approach can be generalized to fields with spin.Comment: uses feynmp macros; v2 contains improved description of
renormalization, plus other minor change
Phenomenology of Quantum Gravity and its Possible Role in Neutrino Anomalies
New phenomenological models of Quantum Gravity have suggested that a
Lorentz-Invariant discrete spacetime structure may become manifest through a
nonstandard coupling of matter fields and spacetime curvature. On the other
hand, there is strong experimental evidence suggesting that neutrino
oscillations cannot be described by simply considering neutrinos as massive
particles. In this manuscript we motivate and construct one particular
phenomenological model of Quantum Gravity that could account for the so-called
neutrino anomalies.Comment: For the proceedings of "Relativity and Gravitation: 100 Years after
Einstein in Prague" (June 2012, Prague
On the evaluation of a certain class of Feynman diagrams in x-space: Sunrise-type topologies at any loop order
We review recently developed new powerful techniques to compute a class of
Feynman diagrams at any loop order, known as sunrise-type diagrams. These
sunrise-type topologies have many important applications in many different
fields of physics and we believe it to be timely to discuss their evaluation
from a unified point of view. The method is based on the analysis of the
diagrams directly in configuration space which, in the case of the sunrise-type
diagrams and diagrams related to them, leads to enormous simplifications as
compared to the traditional evaluation of loops in momentum space. We present
explicit formulae for their analytical evaluation for arbitrary mass
configurations and arbitrary dimensions at any loop order. We discuss several
limiting cases of their kinematical regimes which are e.g. relevant for
applications in HQET and NRQCD.Comment: 100 pages, 16 eps-figures include
US Cosmic Visions: New Ideas in Dark Matter 2017: Community Report
This white paper summarizes the workshop "U.S. Cosmic Visions: New Ideas in
Dark Matter" held at University of Maryland on March 23-25, 2017.Comment: 102 pages + reference