14 research outputs found
Bloch-Nordsieck Thermometers: One-loop Exponentiation in Finite Temperature QED
We study the scattering of hard external particles in a heat bath in a
real-time formalism for finite temperature QED. We investigate the distribution
of the 4-momentum difference of initial and final hard particles in a fully
covariant manner when the scale of the process, , is much larger than the
temperature, . Our computations are valid for all subject to this
constraint. We exponentiate the leading infra-red term at one-loop order
through a resummation of soft (thermal) photon emissions and absorptions. For
, we find that tensor structures arise which are not present at .
These carry thermal signatures. As a result, external particles can serve as
thermometers introduced into the heat bath. We investigate the phase space
origin of and terms.Comment: LaTeX file, 29 pages including 3 figure
Stringent constraint on the scalar-neutrino coupling constant from quintessential cosmology
An extremely light (), slowly-varying scalar
field (quintessence) with a potential energy density as large as 60% of
the critical density has been proposed as the origin of the accelerated
expansion of the Universe at present. The interaction of this smoothly
distributed component with another predominately smooth component, the cosmic
neutrino background, is studied. The slow-roll approximation for generic potentials may then be used to obtain a limit on the scalar-neutrino coupling
constant, found to be many orders of magnitude more stringent than the limits
set by observations of neutrinos from SN 1987A. In addition, if quintessential
theory allows for a violation of the equivalence principle in the sector of
neutrinos, the current solar neutrino data can probe such a violation at the
10^{-10} level.Comment: 7 pages, MPLA in press, some parts disregarded and a footnote adde
Comments on two papers by Kapusta and Wong
We critically examine recently published results on the thermal production of
massive vector bosons in a quark-gluon plasma. We claim the production rate is
a collinear safe observable.Comment: 6 pages LATEX documen
Conformal proper times according to the Woodhouse causal axiomatics of relativistic spacetimes
On the basis of the Woodhouse causal axiomatics, we show that conformal
proper times and an extra variable in addition to those of space and time,
precisely and physically identified from experimental examples, together give a
physical justification for the `chronometric hypothesis' of general relativity.
Indeed, we show that, with a lack of these latter two ingredients, no clock
paradox solution exists in which the clock and message functions are solely at
the origin of the asymmetry. These proper times originate from a given
conformal structure of the spacetime when ascribing different compatible
projective structures to each Woodhouse particle, and then, each defines a
specific Weylian sheaf structure. In addition, the proper time
parameterizations, as two point functions, cannot be defined irrespective of
the processes in the relative changes of physical characteristics. These
processes are included via path-dependent conformal scale factors, which act
like sockets for any kind of physical interaction and also represent the values
of the variable associated with the extra dimension. As such, the differential
aging differs far beyond the first and second clock effects in Weyl geometries,
with the latter finally appearing to not be suitable.Comment: 25 pages, 2 figure
The Strongly Coupled 't Hooft Model on the Lattice
We study the strong coupling limit of the one-flavor and two-flavor massless
't Hooft models, -color , on a lattice. We use
staggered fermions and the Hamiltonian approach to lattice gauge theories. We
show that the one-flavor model is effectively described by the
antiferromagnetic Ising model, whose ground state is the vacuum of the gauge
model in the infinite coupling limit; expanding around this ground state we
derive a strong coupling expansion and compute the lowest lying hadron masses
as well as the chiral condensate of the gauge theory. Our lattice computation
well reproduces the results of the continuum theory. Baryons are massless in
the infinite coupling limit; they acquire a mass already at the second order in
the strong coupling expansion in agreement with the Witten argument that
baryons are the solitons.
The spectrum and chiral condensate of the two-flavor model are effectively
described in terms of observables of the quantum antiferromagnetic Heisenberg
model. We explicitly write the lowest lying hadron masses and chiral condensate
in terms of spin-spin correlators on the ground state of the spin model. We
show that the planar limit () of the gauge
model corresponds to the large spin limit () of the
antiferromagnet and compute the hadron mass spectrum in this limit finding
that, also in this model, the pattern of chiral symmetry breaking of the
continuum theory is well reproduced on the lattice.Comment: LaTex, 25 pages, no figure
Improved lattice QCD with quarks: the 2 dimensional case
QCD in two dimensions is investigated using the improved fermionic lattice
Hamiltonian proposed by Luo, Chen, Xu, and Jiang. We show that the improved
theory leads to a significant reduction of the finite lattice spacing errors.
The quark condensate and the mass of lightest quark and anti-quark bound state
in the strong coupling phase (different from t'Hooft phase) are computed. We
find agreement between our results and the analytical ones in the continuum.Comment: LaTeX file (including text + 10 figures
Status of the wave function of Quantum Mechanics, or, What is Quantum Mechanics trying to tell us?
The most debated status of the wave function of Quantum Mechanics is
discussed in the light of the epistemological vs ontological opposition
Elementary Particles: What are they? Substances, elements and primary matter
The most successful "Standard Model" allows one to define the so-called
"Elementary Particles". Now from another point of view, philosophical, how can
we think of them? Which kind of a status can be attributed to Elementary
Particles and their associated quantised fields? Beyond the unprecedented
efficiency and reach of quantum field theories the current paper attempts at
understanding the nature of what we talk about, the enigmatic reality of the
quantum world