4,596 research outputs found
Impact of off-shell dynamics on the transport properties and the dynamical evolution of Charm Quarks at RHIC and LHC temperatures
We evaluate drag and diffusion transport coefficients comparing a
quasi-particle approximation with on-shell constituents of the QGP medium and a
dynamical quasi-particles model with off-shell bulk medium at finite
temperature T. We study the effects of the width of the particles of
the bulk medium on the charm quark transport properties exploring the range
where . We find that off-shell effects are in general quite
moderate and can induce a reduction of the drag coefficient at low momenta that
disappear already at moderate momenta, . We also
observe a moderate reduction of the breaking of the Fluctuation-Dissipation
theorem (FDT) at finite momenta.
Moreover, we have performed a first study of the dynamical evolution of HQ
elastic energy loss in a bulk medium at fixed temperature extending the
Boltzmann (BM) collision integral to include off-shell dynamics. A comparison
among the Langevin dynamics, the BM collisional integral with on-shell and the
BM extension to off-shell dynamics shows that the evolution of charm energy
when off-shell effects are included remain quite similar to the case of the
on-shell BM collision integral.Comment: 13 pages, 14 figure
Transitory Inhibition of the left anterior intraparietal sulcus impairs joint actions: a continuous Theta-Burst stimulation study
Although temporal coordination is a hallmark of motor interactions, joint action (JA) partners do not simply synchronize; they rather dynamically adapt to each other to achieve a joint goal. We created a novel paradigm to tease apart the processes underlying synchronization and JA and tested the causal contribution of the left anterior intraparietal sulcus (aIPS) in these behaviors. Participants had to synchronize their congruent or incongruent movements with a virtual partner in two conditions: (i) being instructed on what specific action to perform, independently from what action the partner performed (synchronization), and (ii) being instructed to adapt online to the partner's action (JA). Offline noninvasive inhibitory brain stimulation (continuous theta-burst stimulation) over the left aIPS selectively modulated interpersonal synchrony in JA by boosting synchrony during congruent interactions and impairing it during incongruent ones, while leaving performance in the synchronization condition unaffected. These results suggest that the left aIPS plays a causal role in supporting online adaptation to a partner's action goal, whereas it is not necessarily engaged in social situations where the goal of the partner is irrelevant. This indicates that, during JAs, the integration of one's own and the partner's action goal is supported by aIPS
Non-Hermitian Hamiltonian for a Modulated Jaynes-Cummings Model with PT Symmetry
We consider a two-level system such as a two-level atom, interacting with a
cavity field mode in the rotating wave approximation, when the atomic
transition frequency or the field mode frequency is periodically driven in
time. We show that in both cases, for an appropriate choice of the modulation
parameters, the state amplitudes in a generic {-}excitation subspace obey
the same equations of motion that can be obtained from a \emph{static}
non-Hermitian Jaynes-Cummings Hamiltonian with symmetry, that
is with an imaginary coupling constant. This gives further support to recent
results showing the possible physical interest of symmetric
non-Hermitian Hamiltonians. We also generalize the well-known diagonalization
of the Jaynes-Cummings Hamiltonian to the non-Hermitian case in terms of
pseudo-bosons and pseudo-fermions, and discuss relevant mathematical and
physical aspects.Comment: 9 page
Effects of a uniform acceleration on atom-field interactions
We review some quantum electrodynamical effects related to the uniform
acceleration of atoms in vacuum. After discussing the energy level shifts of a
uniformly accelerated atom in vacuum, we investigate the atom-wall
Casimir-Polder force for accelerated atoms, and the van der
Waals/Casimir-Polder interaction between two accelerated atoms. The possibility
of detecting the Unruh effect through these phenomena is also discussed in
detail.Comment: 6 pages. Special Issue: 20th Central European Workshop on Quantum
Optics - Stockholm - June 201
Dynamical Casimir-Polder potentials in non-adiabatic conditions
In this paper we review different aspects of the dynamical Casimir- Polder
potential between a neutral atom and a perfectly conducting plate under
nonequilibrium conditions. In order to calculate the time evolution of the
atom-wall Casimir-Polder potential, we solve the Heisenberg equations
describing the dynamics of the coupled system using an iterative technique.
Different nonequilibrium initial states are considered, such as bare and
partially dressed states. The partially dressed states considered are obtained
by a sudden change of a physical parameter of the atom or of its position
relative to the conducting plate. Experimental feasibility of detecting the
considered dynamical effects is also discussed.Comment: 6 pages; Special Issue: 20th Central European Workshop on Quantum
Optics - Stockholm - June 201
Catching galaxies in the act of quenching star formation
Detecting galaxies when their star-formation is being quenched is crucial to
understand the mechanisms driving their evolution. We identify for the first
time a sample of quenching galaxies selected just after the interruption of
their star formation by exploiting the [O III]5007/Halpha ratio and searching
for galaxies with undetected [O III]. Using a sample of ~174000 star-forming
galaxies extracted from the SDSS-DR8 at 0.04 < z < 0.21,we identify the ~300
quenching galaxy best candidates with low [O III]/Halpha, out of ~26000
galaxies without [O III] emission. They have masses between 10^9.7 and 10^10.8
Mo, consistently with the corresponding growth of the quiescent population at
these redshifts. Their main properties (i.e. star-formation rate, colours and
metallicities) are comparable to those of the star-forming population,
coherently with the hypothesis of recent quenching, but preferably reside in
higher-density environments.Most candidates have morphologies similar to
star-forming galaxies, suggesting that no morphological transformation has
occurred yet. From a survival analysis we find a low fraction of candidates
(~0.58% of the star-forming population), leading to a short quenching timescale
of tQ~50Myr and an e-folding time for the quenching history of tauQ~90Myr, and
their upper limits of tQ<0.76 Gyr and tauQ<1.5Gyr, assuming as quenching
galaxies 50% of objects without [O III] (~7.5%).Our results are compatible with
a 'rapid' quenching scenario of satellites galaxies due to the final phase of
strangulation or ram-pressure stripping. This approach represents a robust
alternative to methods used so far to select quenched galaxies (e.g. colours,
specific star-formation rate, or post-starburst spectra).Comment: 22 pages, 23 figures, accepted for publication in MNRA
Causative role of left aIPS in coding shared goals during human-avatar complementary joint actions
Successful motor interactions require agents to anticipate what a partner is doing in order to predictively adjust their own movements. Although the neural underpinnings of the ability to predict others' action goals have been well explored during passive action observation, no study has yet clarified any critical neural substrate supporting interpersonal coordination during active, non-imitative (complementary) interactions. Here, we combine non-invasive inhibitory brain stimulation (continuous Theta Burst Stimulation) with a novel human-avatar interaction task to investigate a causal role for higher-order motor cortical regions in supporting the ability to predict and adapt to others' actions. We demonstrate that inhibition of left anterior intraparietal sulcus (aIPS), but not ventral premotor cortex, selectively impaired individuals' performance during complementary interactions. Thus, in addition to coding observed and executed action goals, aIPS is crucial in coding 'shared goals', that is, integrating predictions about one's and others' complementary actions
Nonequilibrium dressing in a cavity with a movable reflecting mirror
We consider a movable mirror coupled to a one-dimensional massless scalar
field in a cavity. Both the field and the mirror's mechanical degrees of
freedom are described quantum-mechanically, and they can interact each other
via the radiation pressure operator. We investigate the dynamical evolution of
mirror and field starting from a nonequilibrium initial state, and their local
interaction which brings the system to a stationary configuration for long
times. This allows us to study the time-dependent dressing process of the
movable mirror interacting with the field, and its dynamics leading to a local
equilibrium dressed configuration. Also, in order to explore the effect of the
radiation pressure on both sides of the movable mirror, we generalize the
effective field-mirror Hamiltonian and previous results to the case of two
cavities sharing the same mobile boundary. This leads us to address, in the
appropriate limit, the dynamical dressing problem of a single mobile wall,
bounded by a harmonic potential, in the vacuum space.Comment: 10 pages, 4 figure
Harmonic oscillator model for the atom-surface Casimir-Polder interaction energy
In this paper we consider a quantum harmonic oscillator interacting with the
electromagnetic radiation field in the presence of a boundary condition
preserving the continuous spectrum of the field, such as an infinite perfectly
conducting plate. Using an appropriate Bogoliubov-type transformation we can
diagonalize exactly the Hamiltonian of our system in the continuum limit and
obtain non-perturbative expressions for its ground-state energy. From the
expressions found, the atom-wall Casimir-Polder interaction energy can be
obtained, and well-know lowest-order results are recovered as a limiting case.
Use and advantage of this method for dealing with other systems where
perturbation theory cannot be used is also discussed.Comment: 6 page
A methodology to select galaxies just after the quenching of star formation
We propose a new methodology aimed at finding star-forming galaxies in the
phase which immediately follows the star-formation (SF) quenching, based on the
use of high- to low-ionization emission line ratios. These ratios rapidly
disappear after the SF halt, due to the softening of the UV ionizing radiation.
We focus on [O III] 5007/H and [Ne III] 3869/[O II]
3727, studying them with simulations obtained with the CLOUDY
photoionization code. If a sharp quenching is assumed, we find that the two
ratios are very sensitive tracers as they drop by a factor 10 within
10 Myr from the interruption of the SF; instead, if a smoother and
slower SF decline is assumed (i.e. an exponentially declining star-formation
history with -folding time 200 Myr), they decrease by a factor
2 within 80 Myr. We mitigate the ionization -- metallicity
degeneracy affecting our methodology using pairs of emission line ratios
separately related to metallicity and ionization, adopting the [N II]
6584/[O II] 3727 ratio as metallicity diagnostic. Using a
Sloan Digital Sky Survey galaxy sample, we identify 10 examples among the most
extreme quenching candidates within the [O III] 5007/H vs. [N
II] 6584/[O II] 3727 plane, characterized by low [O III]
5007/H, faint [Ne III] 3869, and by blue
dust-corrected spectra and colours, as expected if the SF quenching has
occurred in the very recent past. Our results also suggest that the observed
fractions of quenching candidates can be used to constrain the quenching
mechanism at work and its time-scales.Comment: Accepted for publication in MNRAS; 19 pages, 21 figures, 1 tabl
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