186 research outputs found
Faraday effect : a field theoretical point of view
We analyze the structure of the vacuum polarization tensor in the presence of
a background electromagnetic field in a medium. We use various discrete
symmetries and crossing symmetry to constrain the form factors obtained for the
most general case. From these symmetry arguments, we show why the vacuum
polarization tensor has to be even in the background field when there is no
background medium. Taking then the background field to be purely magnetic, we
evaluate the vacuum polarization to linear order in it. The result shows the
phenomenon of Faraday rotation, i.e., the rotation of the plane of polarization
of a plane polarized light passing through this background. We find that the
usual expression for Faraday rotation, which is derived for a non-degenerate
plasma in the non-relativistic approximation, undergoes substantial
modification if the background is degenerate and/or relativistic. We give
explicit expressions for Faraday rotation in completely degenerate and
ultra-relativistic media.Comment: 20 pages, Latex, uses axodraw.st
Agro-materials : a bibliographic review
Facing the problems of plastic recycling and fossil resources exhaustion, the use of biomass to conceive new materials appears like a reasonable solution. Two axes of research are nowadays developed : on the one hand the synthesis of biodegradable plastics, whichever the methods may be, on the other hand the utilization of raw biopolymers, which is the object of this paper. From this perspective, the “plastic” properties of natural polymers, the caracteristics of the different classes of polymers, the use of charge in vegetable matrix and the possible means of improving the durability of these agro-materials are reviewed
Two Mathematically Equivalent Versions of Maxwell's Equations
This paper is a review of the canonical proper-time approach to relativistic
mechanics and classical electrodynamics. The purpose is to provide a physically
complete classical background for a new approach to relativistic quantum
theory. Here, we first show that there are two versions of Maxwell's equations.
The new version fixes the clock of the field source for all inertial observers.
However now, the (natural definition of the effective) speed of light is no
longer an invariant for all observers, but depends on the motion of the source.
This approach allows us to account for radiation reaction without the
Lorentz-Dirac equation, self-energy (divergence), advanced potentials or any
assumptions about the structure of the source. The theory provides a new
invariance group which, in general, is a nonlinear and nonlocal representation
of the Lorentz group. This approach also provides a natural (and unique)
definition of simultaneity for all observers. The corresponding particle theory
is independent of particle number, noninvariant under time reversal (arrow of
time), compatible with quantum mechanics and has a corresponding positive
definite canonical Hamiltonian associated with the clock of the source.
We also provide a brief review of our work on the foundational aspects of the
corresponding relativistic quantum theory. Here, we show that the standard
square-root and the Dirac equations are actually two distinct
spin- particle equations.Comment: Appeared: Foundations of Physic
Evolution of Black Holes in the Galaxy
In this article we consider the formation and evolution of black holes,
especially those in binary stars where radiation from the matter falling on
them can be seen. We consider a number of effects introduced by some of us,
which are not traditionally included in binary evolution of massive stars.
These are (i) hypercritical accretion, which allows neutron stars to accrete
enough matter to collapse to a black hole during their spiral-in into another
star. (ii) the strong mass loss of helium stars, which causes their evolution
to differ from that of the helium core of a massive star. (iii) The direct
formation of low-mass black holes (M\sim2\msun) from single stars, a
consequence of a significant strange-matter content of the nuclear-matter
equation of state at high density. We discuss these processes here, and then
review how they affect various populations of binaries with black holes and
neutron stars.Comment: 46 pages, 1 figure, to be published in Physics Repor
Realising the Olympic dream: vision, support and challenge
The sporting arena is replete with examples and anecdotes of great inspirational coaches that have led teams to success, often in the face of adversity and against seemingly better opponents. The role of the coach in developing and motivating athletes has also been the focus of much research in sport psychology (e.g., Challaduria 1990; Smith & Smoll, 2007). Despite the ease with which one readily accepts that coaches can be inspirational, the sport coaching literature is somewhat devoid of research on inspirational coaches and the effects of such coaches on athletic success. The purpose of the current paper is to theoretically delineate the inspirational effects of coaches in sport. Given the relative paucity of inspiration-related research in sport we draw upon contemporary theories of leadership from organisational and military psychology (e.g., transformational and charismatic leadership theories). We propose a sport-specific model of leadership that centres around the vision, support, and challenge meta-cognitive model developed by Arthur and Hardy in military contexts. The model posits that �great� coaches inspire their athletes by: (a) creating an inspirational vision of the future; (b) providing the necessary support to achieve the vision; and (c) providing the challenge to achieve the vision. The underlying proposition is that the vision provides meaning and direction for followers� effort. That is, the vision serves as the beacon around which all the sweat, pain and sacrifice involved in achieving success at the highest level in sport is directed. At the heart of this model is the notion that athletes can achieve their dreams provided they are inspired to do so; this is because all other things being equal the person who is motivated to practice longer and train harder will ultimately be the best. The current paper will delineate the coach�s role in inspiring the athlete to train harder and longer
The integrated Sachs-Wolfe Effect -- Large Scale Structure Correlation
We discuss the correlation between late-time integrated Sachs-Wolfe (ISW)
effect in the cosmic microwave background (CMB) temperature anisotropies and
the large scale structure of the local universe. This correlation has been
proposed and studied in the literature as a probe of the dark energy and its
physical properties. We consider a variety of large scale structure tracers
suitable for a detection of the ISW effect via a cross-correlation. In addition
to luminous sources, we suggest the use of tracers such as dark matter halos or
galaxy clusters. A suitable catalog of mass selected halos for this purpose can
be constructed with upcoming wide-field lensing and Sunyaev-Zel'dovich (SZ)
effect surveys. With multifrequency data, the presence of the ISW-large scale
structure correlation can also be investigated through a cross-correlation of
the frequency cleaned SZ and CMB maps. While convergence maps constructed from
lensing surveys of the large scale structure via galaxy ellipticities are less
correlated with the ISW effect, lensing potentials that deflect CMB photons are
strongly correlated and allow, probably, the best mechanism to study the
ISW-large scale structure correlation with CMB data alone.Comment: 10 Pages, PRD submitte
Spin alignment of leading mesons in hadronic decays
Helicity density matrix elements for inclusive K*(892)^0 mesons from hadronic Z^0 decays have been measured over the full range of K^*0 momentum using data taken with the OPAL experiment at LEP. A preference for occupation of the helicity zero state is observed at all scaled momentum x_p values above 0.3, with the matrix element rho_00 rising to 0.66 +/- 0.11 for x_p > 0.7. The values of the real part of the off-diagonal element rho_1-1 are negative at large x_p, with a weighted average value of -0.09 +/- 0.03 for x_p > 0.3, in agreement with new theoretical predictions based on Standard Model parameters and coherent fragmentation of the qq(bar) system from the Z^0 decay. All other helicity density matrix elements measured are consistent with zero over the entire x_p range. The K^*0 fragmentation function has also been measured and the total rate determined to be 0.74 +/- 0.02 +/- 0.02 K*(892)^0 mesons per hadronic Z^0 decay.Helicity density matrix elements for inclusive K*(892)^0 mesons from hadronic Z^0 decays have been measured over the full range of K^*0 momentum using data taken with the OPAL experiment at LEP. A preference for occupation of the helicity zero state is observed at all scaled momentum x_p values above 0.3, with the matrix element rho_00 rising to 0.66 +/- 0.11 for x_p > 0.7. The values of the real part of the off-diagonal element rho_1-1 are negative at large x_p, with a weighted average value of -0.09 +/- 0.03 for x_p > 0.3, in agreement with new theoretical predictions based on Standard Model parameters and coherent fragmentation of the qq(bar) system from the Z^0 decay. All other helicity density matrix elements measured are consistent with zero over the entire x_p range. The K^*0 fragmentation function has also been measured and the total rate determined to be 0.74 +/- 0.02 +/- 0.02 K*(892)^0 mesons per hadronic Z^0 decay.Helicity density matrix elements for inclusive K*(892)^0 mesons from hadronic Z^0 decays have been measured over the full range of K^*0 momentum using data taken with the OPAL experiment at LEP. A preference for occupation of the helicity zero state is observed at all scaled momentum x_p values above 0.3, with the matrix element rho_00 rising to 0.66 +/- 0.11 for x_p > 0.7. The values of the real part of the off-diagonal element rho_1-1 are negative at large x_p, with a weighted average value of -0.09 +/- 0.03 for x_p > 0.3, in agreement with new theoretical predictions based on Standard Model parameters and coherent fragmentation of the qq(bar) system from the Z^0 decay. All other helicity density matrix elements measured are consistent with zero over the entire x_p range. The K^*0 fragmentation function has also been measured and the total rate determined to be 0.74 +/- 0.02 +/- 0.02 K*(892)^0 mesons per hadronic Z^0 decay.Helicity density matrix elements for inclusive K*(892)^0 mesons from hadronic Z^0 decays have been measured over the full range of K^*0 momentum using data taken with the OPAL experiment at LEP. A preference for occupation of the helicity zero state is observed at all scaled momentum x_p values above 0.3, with the matrix element rho_00 rising to 0.66 +/- 0.11 for x_p > 0.7. The values of the real part of the off-diagonal element rho_1-1 are negative at large x_p, with a weighted average value of -0.09 +/- 0.03 for x_p > 0.3, in agreement with new theoretical predictions based on Standard Model parameters and coherent fragmentation of the qq(bar) system from the Z^0 decay. All other helicity density matrix elements measured are consistent with zero over the entire x_p range. The K^*0 fragmentation function has also been measured and the total rate determined to be 0.74 +/- 0.02 +/- 0.02 K*(892)^0 mesons per hadronic Z^0 decay.Helicity density matrix elements for inclusive K ∗ (892) 0 mesons from hadronic Z 0 decays have been measured over the full range of K ∗ 0 momentum using data taken with the OPAL experiment at LEP. A preference for occupation of the helicity zero state is observed at all scaled momentum x p values above 0.3, with the matrix element ϱ 00 rising to 0.66 ± 0.11 for x p > 0.7. The values of the real part of the off-diagonal element ϱ 1 - 1 are negative at large x p , with a weighted average value of −0.09 ± 0.03 for x p > 0.3, in agreement with new theoretical predictions based on Standard Model parameters and coherent fragmentation of the q q system from the Z 0 decay. All other helicity density matrix elements measured are consistent with zero over the entire x p range. The K ∗ 0 fragmentation function has also been measured and the total rate determined to be 0.74 ± 0.02 ± 0.02 K ∗ (892) 0 mesons per hadronic Z 0 decay
Search for Gravitational Waves Associated with Gamma-Ray Bursts Detected by Fermi and Swift during the LIGO-Virgo Run O3b
We search for gravitational-wave signals associated with gamma-ray bursts (GRBs) detected by the Fermi and Swift satellites during the second half of the third observing run of Advanced LIGO and Advanced Virgo (2019 November 1 15:00 UTC-2020 March 27 17:00 UTC). We conduct two independent searches: A generic gravitational-wave transients search to analyze 86 GRBs and an analysis to target binary mergers with at least one neutron star as short GRB progenitors for 17 events. We find no significant evidence for gravitational-wave signals associated with any of these GRBs. A weighted binomial test of the combined results finds no evidence for subthreshold gravitational-wave signals associated with this GRB ensemble either. We use several source types and signal morphologies during the searches, resulting in lower bounds on the estimated distance to each GRB. Finally, we constrain the population of low-luminosity short GRBs using results from the first to the third observing runs of Advanced LIGO and Advanced Virgo. The resulting population is in accordance with the local binary neutron star merger rate. © 2022. The Author(s). Published by the American Astronomical Society
Narrowband Searches for Continuous and Long-duration Transient Gravitational Waves from Known Pulsars in the LIGO-Virgo Third Observing Run
Isolated neutron stars that are asymmetric with respect to their spin axis are possible sources of detectable continuous gravitational waves. This paper presents a fully coherent search for such signals from eighteen pulsars in data from LIGO and Virgo's third observing run (O3). For known pulsars, efficient and sensitive matched-filter searches can be carried out if one assumes the gravitational radiation is phase-locked to the electromagnetic emission. In the search presented here, we relax this assumption and allow both the frequency and the time derivative of the frequency of the gravitational waves to vary in a small range around those inferred from electromagnetic observations. We find no evidence for continuous gravitational waves, and set upper limits on the strain amplitude for each target. These limits are more constraining for seven of the targets than the spin-down limit defined by ascribing all rotational energy loss to gravitational radiation. In an additional search, we look in O3 data for long-duration (hours-months) transient gravitational waves in the aftermath of pulsar glitches for six targets with a total of nine glitches. We report two marginal outliers from this search, but find no clear evidence for such emission either. The resulting duration-dependent strain upper limits do not surpass indirect energy constraints for any of these targets. © 2022. The Author(s). Published by the American Astronomical Society
- …