7,704 research outputs found
Covariant Helicity-Coupling Amplitudes: A New Formulation
We have worked out covariant amplitudes for any two-body decay of a resonance
with an arbitrary non-zero mass, which involves arbitrary integer spins in the
initial and the final states. One key new ingredient for this work is the
application of the total intrinsic spin operator which is given
directly in terms of the generators of the Poincar\'e group.
Using the results of this study, we show how to explore the Lorentz factors
which appear naturally, if the momentum-space wave functions are used to form
the covariant decay amplitudes. We have devised a method of constructing our
covariant decay amplitudes, such that they lead to the Zemach amplitudes when
the Lorentz factors are set one
Mechanically Detecting and Avoiding the Quantum Fluctuations of a Microwave Field
During the theoretical investigation of the ultimate sensitivity of
gravitational wave detectors through the 1970's and '80's, it was debated
whether quantum fluctuations of the light field used for detection, also known
as photon shot noise, would ultimately produce a force noise which would
disturb the detector and limit the sensitivity. Carlton Caves famously answered
this question with "They do." With this understanding came ideas how to avoid
this limitation by giving up complete knowledge of the detector's motion. In
these back-action evading (BAE) or quantum non-demolition (QND) schemes, one
manipulates the required quantum measurement back-action by placing it into a
component of the motion which is unobserved and dynamically isolated. Using a
superconducting, electro-mechanical device, we realize a sensitive measurement
of a single motional quadrature with imprecision below the zero-point
fluctuations of motion, detect both the classical and quantum measurement
back-action, and demonstrate BAE avoiding the quantum back-action from the
microwave photons by 9 dB. Further improvements of these techniques are
expected to provide a practical route to manipulate and prepare a squeezed
state of motion with mechanical fluctuations below the quantum zero-point
level, which is of interest both fundamentally and for the detection of very
weak forces
Putative spin liquid in the triangle-based iridate BaIrTiO
We report on thermodynamic, magnetization, and muon spin relaxation
measurements of the strong spin-orbit coupled iridate BaIrTiO,
which constitutes a new frustration motif made up a mixture of edge- and
corner-sharing triangles. In spite of strong antiferromagnetic exchange
interaction of the order of 100~K, we find no hint for long-range magnetic
order down to 23 mK. The magnetic specific heat data unveil the -linear and
-squared dependences at low temperatures below 1~K. At the respective
temperatures, the zero-field muon spin relaxation features a persistent spin
dynamics, indicative of unconventional low-energy excitations. A comparison to
the isostructural compound BaRuTiO suggests that a concerted
interplay of compass-like magnetic interactions and frustrated geometry
promotes a dynamically fluctuating state in a triangle-based iridate.Comment: Physical Review B accepte
Bremsstrahlung photon polarization for , and high energy collisions
The polarization of bremsstrahlung photon in the processes , and is calculated for peripheral
kinematics, in the high energy limit where the cross section does not decrease
with the incident energy. When the initial electron is
unpolarized(longitudinally polarized) the final photon can be linearly
(circularly) polarized. The Stokes parameters of the photon polarization are
calculated as a function of the kinematical variables of process: the energy of
recoil particle, the energy fraction of scattered electron, and the polar and
azimuthal angles of photon. Numerical results are given in form of tables, for
typical values of the relevant kinematic variables.Comment: 9 pages, 3 figure
Interplay between carrier and impurity concentrations in annealed GaMnAs intrinsic anomalous Hall Effect
Investigating the scaling behavior of annealed GaMnAs anomalous
Hall coefficients, we note a universal crossover regime where the scaling
behavior changes from quadratic to linear, attributed to the anomalous Hall
Effect intrinsic and extrinsic origins, respectively. Furthermore, measured
anomalous Hall conductivities when properly scaled by carrier concentration
remain constant, equal to theoretically predicated values, spanning nearly a
decade in conductivity as well as over 100 K in T. Both the qualitative
and quantitative agreement confirms the validity of new equations of motion
including the Berry phase contributions as well as tunablility of the intrinsic
anomalous Hall Effect.Comment: 4 pages, 5 figure
Spin Dynamics in the LTT Phase of ~1/8 Doped Single Crystal La_{1.67}Eu_{0.2}Sr_{0.13}CuO_4
We present La and Cu NMR relaxation measurements in single crystal
La_{1.67}Eu_{0.2}Sr_{0.13}CuO_4. A strong peak in the La spin-lattice
relaxation rate observed in the spin ordered state is well-described by the BPP
mechanism[1] and arises from continuous slowing of electronic spin fluctuations
with decreasing temperature; these spin fluctuations exhibit XY-like anisotropy
in the ordered state. The spin pseudogap is enhanced by the static
charge-stripe order in the LTT phase.Comment: Four pages, three figure
An extreme [OIII] emitter at : a low metallicity Lyman continuum source
[Abridged] We investigate the physical properties of a Lyman continuum
emitter candidate at with photometric coverage from to MIPS
24m band and VIMOS/VLT and MOSFIRE/Keck spectroscopy. Investigation of the
UV spectrum confirms a direct spectroscopic detection of the Lyman continuum
emission with . Non-zero Ly flux at the systemic redshift and
high Lyman- escape fraction suggest a low HI column density. The weak C
and Si low-ionization absorption lines are also consistent with a low covering
fraction along the line of sight. The
[OIII] equivalent width is one of the
largest reported for a galaxy at
(, rest-frame) and the NIR spectrum shows that this is mainly due to an
extremely strong [OIII] emission. The large observed [OIII]/[OII] ratio ()
and high ionization parameter are consistent with prediction from
photoionization models in case of a density-bounded nebula scenario.
Furthermore, the
is
comparable to recent measurements reported at , in the reionization
epoch. We also investigate the possibility of an AGN contribution to explain
the ionizing emission but most of the AGN identification diagnostics suggest
that stellar emission dominates instead. This source is currently the first
high- example of a Lyman continuum emitter exhibiting indirect and direct
evidences of a Lyman continuum leakage and having physical properties
consistent with theoretical expectation from Lyman continuum emission from a
density-bounded nebula.Comment: 14 pages, 11 figures, accepted for publication in A&A. Minor
modifications, Figure 2 updated, Figure 9 adde
Cold ideal equation of state for strongly magnetized neutron-star matter: effects on muon production and pion condensationn
Neutron stars with very strong surface magnetic fields have been suggested as
the site for the origin of observed soft gamma repeaters (SGRs). In this paper
we investigate the influence of such strong magnetic fields on the properties
and internal structure of these magnetized neutron stars (magnetars). We study
properties of a degenerate equilibrium ideal neutron-proton-electron (npe) gas
with and without the effects of the anomalous nucleon magnetic moments in a
magnetic field. The presence of a sufficiently strong magnetic field changes
the ratio of protons to neutrons as well as the neutron drip density. We also
study the appearance of muons as well as pion condensation in strong magnetic
fields. We discuss the possibility that boson condensation in the interior of
magnetars might be a source of SGRs.Comment: 10 pages included 9 figures, ApJ in pres
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