30,926 research outputs found
The space-time structure of hard scattering processes
Recent studies of exclusive electroproduction of vector mesons at JLab make
it possible for the first time to play with two independent hard scales: the
virtuality Q^2 of the photon, which sets the observation scale, and the
momentum transfer t to the hadronic system, which sets the interaction scale.
They reinforce the description of hard scattering processes in terms of few
effective degrees of freedom relevant to the Jlab-Hermes energy range.Comment: 4 pages; 5 figure
Mean eigenvalues for simple, simply connected, compact Lie groups
We determine for each of the simple, simply connected, compact and complex
Lie groups SU(n), Spin and that particular region inside the unit
disk in the complex plane which is filled by their mean eigenvalues. We give
analytical parameterizations for the boundary curves of these so-called trace
figures. The area enclosed by a trace figure turns out to be a rational
multiple of in each case. We calculate also the length of the boundary
curve and determine the radius of the largest circle that is contained in a
trace figure. The discrete center of the corresponding compact complex Lie
group shows up prominently in the form of cusp points of the trace figure
placed symmetrically on the unit circle. For the exceptional Lie groups ,
and with trivial center we determine the (negative) lower bound on
their mean eigenvalues lying within the real interval . We find the
rational boundary values -2/7, -3/13 and -1/31 for , and ,
respectively.Comment: 12 pages, 8 figure
Elective Modernism and the Politics of (Bio) Ethical Expertise
In this essay I consider whether the political perspective of third wave science studies – ‘elective modernism’ – offers a suitable framework for understanding the policy-making contributions that (bio)ethical experts might make. The question arises as a consequence of the fact that I have taken inspiration from the third wave in order to develop an account of (bio)ethical expertise. I offer a précis of this work and a brief summary of elective modernism before considering their relation. The view I set out suggests that elective modernism is a political philosophy and that although its use in relation to the use of scientific expertise in political and policy-making process has implications for the role of (bio)ethical expertise it does not, in the final analysis, provide an account that is appropriate for this latter form of specialist expertise. Nevertheless, it is an informative perspective, and one that can help us make sense of the political uses of (bio)ethical expertise
Long distance quantum teleportation in a quantum relay configuration
A long distance quantum teleportation experiment with a fiber-delayed Bell
State Measurement (BSM) is reported. The source creating the qubits to be
teleported and the source creating the necessary entangled state are connected
to the beam splitter realizing the BSM by two 2 km long optical fibers. In
addition, the teleported qubits are analyzed after 2,2 km of optical fiber, in
another lab separated by 55 m. Time bin qubits carried by photons at 1310 nm
are teleported onto photons at 1550 nm. The fidelity is of 77%, above the
maximal value obtainable without entanglement. This is the first realization of
an elementary quantum relay over significant distances, which will allow an
increase in the range of quantum communication and quantum key distribution.Comment: 4 pages, submitte
Gribov horizon and i-particles: about a toy model and the construction of physical operators
Restricting the functional integral to the Gribov region leads to a
deep modification of the behavior of Euclidean Yang-Mills theories in the
infrared region. For example, a gluon propagator of the Gribov type,
, can be viewed as a propagating pair of
unphysical modes, called here -particles, with complex masses . From this viewpoint, gluons are unphysical and one can see them as
being confined. We introduce a simple toy model describing how a suitable set
of composite operators can be constructed out of -particles whose
correlation functions exhibit only real branch cuts, with associated positive
spectral density. These composite operators can thus be called physical and are
the toy analogy of glueballs in the Gribov-Zwanziger theory.Comment: 35 pages, 10 .pdf figures. v2: version accepted for publication in
Physical Review
Thermopower as a Possible Probe of Non-Abelian Quasiparticle Statistics in Fractional Quantum Hall Liquids
We show in this paper that thermopower is enhanced in non-Abelian quantum
Hall liquids under appropriate conditions. This is because thermopower measures
entropy per electron in the clean limit, while the degeneracy and entropy
associated with non-Abelian quasiparticles enhance entropy when they are
present. Thus thermopower can potentially probe non-Abelian nature of the
quasiparticles, and measure their quantum dimension.Comment: 5 pages. Minor revisions in response to referee comments. Published
versio
A Crystallographic Basis for Critically Evaluating the Mechanisms for Secondary Grain Formation During Directional Solidification
Backreaction in trans-Planckian cosmology: renormalization, trace anomaly and selfconsistent solutions
We analyze the semiclassical Einstein equations for quantum scalar fields
satisfying modified dispersion relations. We first discuss in detail the
renormalization procedure based on adiabatic subtraction and dimensional
regularization. We show that, contrary to what expected from power counting
arguments, in 3+1 dimensions the subtraction involves up to the fourth
adiabatic order even for dispersion relations containing higher powers of the
momentum. Then we analyze the dependence of the trace of the renormalized
energy momentum tensor with the scale of new physics, and we recover the usual
trace anomaly in the appropriate limit. We also find selfconsistent de Sitter
solutions for dispersion relations that contain up to the fourth power of the
momentum. Using this particular example, we also discuss the possibility that
the modified dispersion relation can be mimicked at lower energies by an
effective initial state in a theory with the usual dispersion relation.Comment: 19 pages, 3 figure
Calculation of a Deuterium Double Shock Hugoniot from Ab initio Simulations
We calculate the equation of state of dense deuterium with two ab initio
simulations techniques, path integral Monte Carlo and density functional theory
molecular dynamics, in the density range of 0.67 < rho < 1.60 g/cc. We derive
the double shock Hugoniot and compare with the recent laser-driven double shock
wave experiments by Mostovych et al. [1]. We find excellent agreement between
the two types of microscopic simulations but a significant discrepancy with the
laser-driven shock measurements.Comment: accept for publication in Phys. Rev. Lett., Nov. 2001, 4 pages, 4
figure
Quantum Criticality in an Organic Magnet
Exchange interactions between sites in piperazinium
hexachlorodicuprate produce a frustrated bilayer magnet with a singlet ground
state. We have determined the field-temperature phase diagram by high field
magnetization and neutron scattering experiments. There are two quantum
critical points: T separates a quantum paramagnet phase from a
three dimensional, antiferromagnetically-ordered state while T
marks the onset of a fully polarized state. The ordered phase, which we
describe as a magnon Bose-Einstein condensate (BEC), is embedded in a quantum
critical regime with short range correlations. A low temperature anomaly in the
BEC phase boundary indicates that additional low energy features of the
material become important near .Comment: 4 pages, 4 figures, submitted to Phys. Rev. Lett. Replaced original
text with additional conten
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