41,789 research outputs found
Comments concerning the paper "Measurement of negatively charged pion spectra in inelastic p+p interactions at 20, 31, 40, 80 and 158 GeV/c" by the NA61 collaboration
New data from the NA61 collaboration on the production of negative pions in
p+p interactions at beam momenta between 20 and 158 GeV/c are critically
compared to available results in the same energy range. It is concluded that
the NA61 data show some discrepancies with the previous results. This concerns
in particular the total yields, the integrated rapidity distributions and
the double differential cross sections.Comment: 16 pages, 13 figure
Frequency versus relaxation oscillations in a semiconductor laser with coherent filtered optical feedback
We investigate the dynamics of a semiconductor laser subject to coherent delayed filtered optical feedback. A systematic bifurcation analysis reveals that this system supports two fundamentally different types of oscillations, namely relaxation oscillations and external roundtrip oscillations. Both occur stably in large domains under variation of the feedback conditions, where the feedback phase is identified as a key quantity for controlling this dynamical complexity. We identify two separate parameter regions of stable roundtrip oscillations, which occur throughout in the form of pure frequency oscillations
When is an alternative possibility robust?
According to some, free will requires alternative possibilities. But not any old alternative possibility will do. Sometimes, being able to bring about an alternative does not bestow any control on an agent. In order to bestow control, and so be directly relevant qua alternative to grounding the agent's moral responsibility, alternatives need to be robust. Here, I investigate the nature of robust alternatives. I argue that Derk Pereboom's latest robustness criterion is too strong, and I suggest a different criterion based on the idea that what agents need to be able to do is keep open the possibility of securing their blamelessness, rather than needing to directly ensure their own blamelessness at the time of decision
Dicke quantum spin glass of atoms and photons
Recent studies of strongly interacting atoms and photons in optical cavities
have rekindled interest in the Dicke model of atomic qubits coupled to discrete
photon cavity modes. We study the multimode Dicke model with variable
atom-photon couplings. We argue that a quantum spin glass phase can appear,
with a random linear combination of the cavity modes superradiant. We compute
atomic and photon spectral response functions across this quantum phase
transition, both of which should be accessible in experiment.Comment: 4 pages, 3 figures, v2: described quantum optics set-up in more
detail; extended discussion on photon correlation functions and experimental
signatures; added reference
Free-induction decay and envelope modulations in a narrowed nuclear spin bath
We evaluate free-induction decay for the transverse components of a localized
electron spin coupled to a bath of nuclear spins via the Fermi contact
hyperfine interaction. Our perturbative treatment is valid for special
(narrowed) bath initial conditions and when the Zeeman energy of the electron
exceeds the total hyperfine coupling constant : . Using one unified
and systematic method, we recover previous results reported at short and long
times using different techniques. We find a new and unexpected modulation of
the free-induction-decay envelope, which is present even for a purely isotropic
hyperfine interaction without spin echoes and for a single nuclear species. We
give sub-leading corrections to the decoherence rate, and show that, in
general, the decoherence rate has a non-monotonic dependence on electron Zeeman
splitting, leading to a pronounced maximum. These results illustrate the
limitations of methods that make use of leading-order effective Hamiltonians
and re-exponentiation of short-time expansions for a strongly-interacting
system with non-Markovian (history-dependent) dynamics.Comment: 13 pages, 9 figure
Glycerol confined in zeolitic imidazolate frameworks: The temperature-dependent cooperativity length scale of glassy freezing
In the present work, we employ broadband dielectric spectroscopy to study the
molecular dynamics of the prototypical glass former glycerol confined in two
microporous zeolitic imidazolate frameworks (ZIF-8 and ZIF-11) with
well-defined pore diameters of 1.16 and 1.46 nm, respectively. The spectra
reveal information on the modified alpha relaxation of the confined supercooled
liquid, whose temperature dependence exhibits clear deviations from the typical
super-Arrhenius temperature dependence of the bulk material, depending on
temperature and pore size. This allows assigning well-defined cooperativity
length scales of molecular motion to certain temperatures above the glass
transition. We relate these and previous results on glycerol confined in other
host systems to the temperature-dependent length scale deduced from nonlinear
dielectric measurements. The combined experimental data can be consistently
described by a critical divergence of this correlation length as expected
within theoretical approaches assuming that the glass transition is due to an
underlying phase transition.Comment: 14 pages, 5 figures + Supplemental Material (4 pages, 6 figures).
Final version as accepted for publicatio
A survey of backward proton and pion production in p+C interactions at beam momenta from 1 to 400 GeV/c
New data on proton and pion production in p+C interactions from the CERN PS
and SPS accelerators are used in conjunction with other available data sets to
perform a comprehensive survey of backward hadronic cross sections. This survey
covers the complete backward hemisphere in the range of lab angles from 10 to
180 degrees, from 0.2 to 1.4 GeV/c in lab momentum and from 1 to 400 GeV/c in
projectile momentum. Using the constraints of continuity and smoothness of the
angular, momentum and energy dependences a consistent description of the
inclusive cross sections is established which allows the control of the
internal consistency of the nineteen available data sets.Comment: 52 pages 47 figure
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