1,523 research outputs found
Diagonal Slice Four-Wave Mixing: Natural Separation of Coherent Broadening Mechanisms
We present an ultrafast coherent spectroscopy data acquisition scheme that
samples slices of the time domain used in multidimensional coherent
spectroscopy to achieve faster data collection than full spectra. We derive
analytical expressions for resonance lineshapes using this technique that
completely separate homogeneous and inhomogeneous broadening contributions into
separate projected lineshapes for arbitrary inhomogeneous broadening. These
lineshape expressions are also valid for slices taken from full
multidimensional spectra and allow direct measurement of the parameters
contributing to the lineshapes in those spectra as well as our own
Reconciling threshold and subthreshold expansions for pion-nucleon scattering
Heavy-baryon chiral perturbation theory (ChPT) at one loop fails in relating
the pion-nucleon amplitude in the physical region and for subthreshold
kinematics due to loop effects enhanced by large low-energy constants. Studying
the chiral convergence of threshold and subthreshold parameters up to fourth
order in the small-scale expansion, we address the question to what extent this
tension can be mitigated by including the as an explicit degree
of freedom and/or using a covariant formulation of baryon ChPT. We find that
the inclusion of the indeed reduces the low-energy constants to more
natural values and thereby improves consistency between threshold and
subthreshold kinematics. In addition, even in the -less theory the
resummation of corrections in the covariant scheme improves the results
markedly over the heavy-baryon formulation, in line with previous observations
in the single-baryon sector of ChPT that so far have evaded a profound
theoretical explanation.Comment: 10 pages, 4 tables, Mathematica notebook with the analytic
expressions for threshold and subthreshold parameters included as
supplementary material; journal versio
Pion-nucleon scattering in covariant baryon chiral perturbation theory with explicit Delta resonances
We present the results of a third order calculation of the pion-nucleon
scattering amplitude in a chiral effective field theory with pions, nucleons
and delta resonances as explicit degrees of freedom. We work in a manifestly
Lorentz invariant formulation of baryon chiral perturbation theory using
dimensional regularization and the extended on-mass-shell renormalization
scheme. In the delta resonance sector, the on mass-shell renormalization is
realized as a complex-mass scheme. By fitting the low-energy constants of the
effective Lagrangian to the - and -partial waves a satisfactory
description of the phase shifts from the analysis of the Roy-Steiner equations
is obtained. We predict the phase shifts for the and waves and compare
them with the results of the analysis of the George Washington University
group. The threshold parameters are calculated both in the delta-less and
delta-full cases. Based on the determined low-energy constants, we discuss the
pion-nucleon sigma term. Additionally, in order to determine the strangeness
content of the nucleon, we calculate the octet baryon masses in the presence of
decuplet resonances up to next-to-next-to-leading order in SU(3) baryon chiral
perturbation theory. The octet baryon sigma terms are predicted as a byproduct
of this calculation.Comment: 41 pages, 12 figures, 7 table
Non-Markovian large amplitude motion and nuclear fission
The general problem of dissipation in macroscopic large-amplitude collective
motion and its relation to energy diffusion of intrinsic degrees of freedom of
a nucleus is studied. By applying the cranking approach to the nuclear many
body system, a set of coupled dynamical equations for the collective classical
variables and the quantum mechanical occupancies of the intrinsic nuclear
states is derived. Different dynamical regimes of the intrinsic nuclear motion
and its consequences on time properties of collective dissipation are
discussed. The approach is applied to the descant of the nucleus from the
fission barrier.Comment: 9 pages and 3 figure
Neutrino-induced fission of neutron-rich nuclei
We calculate neutrino-induced fission cross sections for selected nuclei with
Z=84-92. We show that these reactions populate the daughter nucleus at
excitation energies where shell effects are significantly washed out,
effectively reducing the fission barrier. If the r-process occurs in the
presence of a strong neutrino fluence, and electron neutrino average energies
are sufficiently high, perhaps as a result of matter-enhanced neutrino flavor
transformation, then neutrino-induced fission could lead to significant
alteration in the r-process flow in slow outflow scenarios.Comment: 4 pages, three figure
Initial Optical Vortex Amplitude Structure Determines Pair Annihilation
We show that annihilation dynamics between oppositely charged optical vortex
pairs can be manipulated by modifying only the initial size of the vortex
cores. When sufficiently close together, vortices with strongly overlapped
cores annihilate more quickly than vortices with smaller cores that must wait
for diffraction to cause meaningful core overlap. We present numerical
simulations and experimental measurements for vortices with hyperbolic tangent
cores of various initial sizes. We also show that decreasing the core size of
an annihilating pair can prevent the annihilation event
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