2,722 research outputs found
On the parameterization dependence of the energy momentum tensor and the metric
We use results by Kirilin to show that in general relativity the nonleading
terms in the energy-momentum tensor of a particle depends on the
parameterization of the gravitational field. While the classical metric that is
calculated from this source, used to define the leading long-distance
corrections to the metric, also has a parameteriztion dependence, it can be
removed by a coordinate change. Thus the classical observables are
parameterization independent. The quantum effects that emerge within the same
calculation of the metric also depend on the parameterization and a full
quantum calculation requires the inclusion of further diagrams. However, within
a given parameterization the quantum effects calculated by us in a previous
paper are well defined. Flaws of Kirilin's proposed alternate metric definition
are described and we explain why the diagrams that we calculated are the
appropriate ones.Comment: 8 pages, 2 figure
On the Ultraviolet Behaviour of Newton's constant
We clarify a point concerning the ultraviolet behaviour of the Quantum Field
Theory of gravity, under the assumption of the existence of an ultraviolet
Fixed Point. We explain why Newton's constant should to scale like the inverse
of the square of the cutoff, even though it is technically inessential. As a
consequence of this behaviour, the existence of an UV Fixed Point would seem to
imply that gravity has a built-in UV cutoff when described in Planck units, but
not necessarily in other units.Comment: 8 pages; CQG class; minor changes and rearrangement
The Electromagnetic Mass Differences of Pions and Kaons
We use the Cottingham method to calculate the pion and kaon electromagnetic
mass differences with as few model dependent inputs as possible. The
constraints of chiral symmetry at low energy, QCD at high energy and
experimental data in between are used in the dispersion relation. We find
excellent agreement with experiment for the pion mass difference. The kaon mass
difference exhibits a strong violation of the lowest order prediction of
Dashen's theorem, in qualitative agreement with several other recent
calculations.Comment: 40 pages, Latex, needs axodraw. and psfig. macros, 4 figure
Fermion masses in noncommutative geometry
Recent indications of neutrino oscillations raise the question of the
possibility of incorporating massive neutrinos in the formulation of the
Standard Model (SM) within noncommutative geometry (NCG). We find that the NCG
requirement of Poincare duality constrains the numbers of massless quarks and
neutrinos to be unequal unless new fermions are introduced. Possible scenarios
in which this constraint is satisfied are discussed.Comment: 4 pages, REVTeX; typos are corrected in (19), "Possible Solutions"
and "Conclusion" are modified; additional calculational details are included;
references are update
Photon-Photon Scattering, Pion Polarizability and Chiral Symmetry
Recent attempts to detect the pion polarizability via analysis of
measurements are examined. The connection
between calculations based on dispersion relations and on chiral perturbation
theory is established by matching the low energy chiral amplitude with that
given by a full dispersive treatment. Using the values for the polarizability
required by chiral symmetry, predicted and experimental cross sections are
shown to be in agreement.Comment: 21 pages(+10 figures available on request), LATEX, UMHEP-38
Cosmological Consequences of String Axions
Axion fluctuations generated during inflation lead to isocurvature and
non-Gaussian temperature fluctuations in the cosmic microwave background
radiation. Following a previous analysis for the model independent string axion
we consider the consequences of a measurement of these fluctuations for two
additional string axions. We do so independent of any cosmological assumptions
except for the axions being massless during inflation. The first axion has been
shown to solve the strong CP problem for most compactifications of the
heterotic string while the second axion, which does not solve the strong CP
problem, obeys a mass formula which is independent of the axion scale. We find
that if gravitational waves interpreted as arising from inflation are observed
by the PLANCK polarimetry experiment with a Hubble constant during inflation of
H_inf \apprge 10^13 GeV the existence of the first axion is ruled out and the
second axion cannot obey the scale independent mass formula. In an appendix we
quantitatively justify the often held assumption that temperature corrections
to the zero temperature QCD axion mass may be ignored for temperatures T
\apprle \Lambda_QCD.Comment: 27 pages, 4 figures; v2: References corrected; v3: Assumptions
simplified, minor corrections, conclusions unchange
Classical Physics and Quantum Loops
The standard picture of the loop expansion associates a factor of h-bar with
each loop, suggesting that the tree diagrams are to be associated with
classical physics, while loop effects are quantum mechanical in nature. We
discuss examples wherein classical effects arise from loop contributions and
display the relationship between the classical terms and the long range effects
of massless particles.Comment: 15 pages, 3 figure
Asymptotic Limits and Structure of the Pion Form Factor
We use dispersive techniques to address the behavior of the pion form factor
as and . We perform the matching with the
constraints of perturbative QCD and chiral perturbation theory in the high
energy and low energy limits, leading to four sum rules. We present a version
of the dispersive input which is consistent with the data and with all
theoretical constraints. The results indicate that the asymptotic perturbative
QCD limit is approached relatively slowly, and give a model independent
determination of low energy chiral parameters.Comment: 8 pages, Latex, 2 figure
Baryon magnetic moments and sigma terms in lattice-regularized chiral perturbation theory
An SU(3) chiral Lagrangian for the lightest decuplet of baryons is
constructed on a discrete lattice of spacetime points, and is added to an
existing lattice Lagrangian for the lightest octets of mesons and baryons. A
nonzero lattice spacing renders all loop integrations finite, and the continuum
limit of any physical observable is identical to the result obtained from
dimensional regularization. Chiral symmetry and gauge invariance are preserved
even at nonzero lattice spacing. Specific calculations discussed here include
the non-renormalization of a conserved vector current, the magnetic moments of
octet baryons, and the pi N and KN sigma terms that relate to the nucleon's
strangeness content. The quantitative difference between physics at a nonzero
lattice spacing and physics in the continuum limit is easily computed, and it
represents an expectation for the size of discretization errors in
corresponding lattice QCD simulations.Comment: 19 pages, 5 figures, one paragraph added to introduction, to appear
in Phys Rev
Enhanced chiral logarithms in partially quenched QCD
I discuss the properties of pions in ``partially quenched'' theories, i.e.
those in which the valence and sea quark masses, and , are
different. I point out that for lattice fermions which retain some chiral
symmetry on the lattice, e.g. staggered fermions, the leading order prediction
of the chiral expansion is that the mass of the pion depends only on , and
is independent of . This surprising result is shown to receive corrections
from loop effects which are of relative size , and which thus
diverge when the valence quark mass vanishes. Using partially quenched chiral
perturbation theory, I calculate the full one-loop correction to the mass and
decay constant of pions composed of two non-degenerate quarks, and suggest
various combinations for which the prediction is independent of the unknown
coefficients of the analytic terms in the chiral Lagrangian. These results can
also be tested with Wilson fermions if one uses a non-perturbative definition
of the quark mass.Comment: 14 pages, 3 figures, uses psfig. Typos in eqs (18)-(20) corrected
(alpha_4 is replaced by alpha_4/2
- …