1,867 research outputs found
Shortcuts to Adiabaticity Assisted by Counterdiabatic Born-Oppenheimer Dynamics
Shortcuts to adiabaticity (STA) provide control protocols to guide the
dynamics of a quantum system through an adiabatic reference trajectory in an
arbitrary prescheduled time. Designing STA proves challenging in complex
quantum systems when the dynamics of the degrees of freedom span different time
scales. We introduce Counterdiabatic Born-Oppenheimer Dynamics (CBOD) as a
framework to design STA in systems with a large separation of energy scales.
CBOD exploits the Born-Oppenheimer approximation to separate the Hamiltonian
into effective fast and slow degrees of freedom and calculate the corresponding
counterdiabatic drivings for each subsystem. We show the validity of the CBOD
technique via an example of coupled harmonic oscillators, which can be solved
exactly for comparison, and further apply it to a system of two-charged
particles.Comment: 14 pages, 3 figures, published New Journal of Physic
Non Singular Origin of the Universe and its Present Vacuum Energy Density
We consider a non singular origin for the Universe starting from an Einstein
static Universe, the so called "emergent universe" scenario, in the framework
of a theory which uses two volume elements and , where is a metric independent density, used as an additional
measure of integration. Also curvature, curvature square terms and for scale
invariance a dilaton field are considered in the action. The first order
formalism is applied. The integration of the equations of motion associated
with the new measure gives rise to the spontaneous symmetry breaking (S.S.B) of
scale invariance (S.I.). After S.S.B. of S.I., it is found that a non trivial
potential for the dilaton is generated. In the Einstein frame we also add a
cosmological term that parametrizes the zero point fluctuations. The resulting
effective potential for the dilaton contains two flat regions, for relevant for the non singular origin of the Universe,
followed by an inflationary phase and , describing
our present Universe. The dynamics of the scalar field becomes non linear and
these non linearities are instrumental in the stability of some of the emergent
universe solutions, which exists for a parameter range of values of the vacuum
energy in , which must be positive but not very big,
avoiding the extreme fine tuning required to keep the vacuum energy density of
the present universe small. Zero vacuum energy density for the present universe
defines the threshold for the creation of the universe.Comment: 28 pages, short version of this paper awarded an honorable mention by
the Gravity Research Foundation, 2011, accepted for publication in
International Journal of Modern Physics
Diffraction in time of a confined particle and its Bohmian paths
Diffraction in time of a particle confined in a box which its walls are
removed suddenly at is studied. The solution of the time-dependent
Schr\"{o}dinger equation is discussed analytically and numerically for various
initial wavefunctions. In each case Bohmian trajectories of the particles are
computed and also the mean arrival time at a given location is studied as a
function of the initial state.Comment: 8 pages, 6 figure
Matter-wave diffraction in time with a linear potential
Diffraction in time of matter waves incident on a shutter which is removed at
time is studied in the presence of a linear potential. The solution is
also discussed in phase space in terms of the Wigner function. An alternative
configuration relevant to current experiments where particles are released from
a hard wall trap is also analyzed for single-particle states and for a
Tonks-Girardeau gas.Comment: 11 pages, 6 figure
Quenched Dynamics of Artificial Spin Ice: Coarsening versus Kibble-Zurek
Artificial spin ices are ideal frustrated model systems in which to explore
or design emergent phenomena with unprecedented characterization of the
constituent degrees of freedom. In square spin ice, violations of the ice rule
are topological excitations essential to the kinetics of the system, providing
an ideal testbed for studying the dynamics of such defects under varied quench
rates. In this work we describe the first test of the Kibble-Zurek mechanism
and critical coarsening in colloidal square and colloidal hexagonal ice under
quenches from a weakly interacting liquid state into a strongly interacting
regime. As expected, for infinitely slow quenches, the system is defect free,
while for increasing quench rate, an increasing number of defects remain in the
sample. For square ice, we find regimes in which the defect population
decreases as a power law with decreasing quench rate. A detailed scaling
analysis shows that for a wide range of parameters, including quench rates that
are accessible by experiments, the behavior is described by critical coarsening
rather than by the Kibble-Zurek mechanism, since the defect-defect interactions
are long ranged. For quenches closer to the critical point, however, there can
be a competition between the two mechanisms.Comment: 7 pages, 6 figure
diagnostics on the nature of dark energy
The two dominant components of the cosmic budget today, pressureles matter
and dark energy, may or may not be interacting with each other. Currently, both
possibilities appear compatible with observational data. We propose several
criteria based on the history of the Hubble factor that can help discern
whether they are interacting and whether dark energy is phantom or quintessence
in nature.Comment: 22 pages, 7 figures. Accepted for publication in IJMP
Exact propagators for atom-laser interactions
A class of exact propagators describing the interaction of an -level atom
with a set of on-resonance -lasers is obtained by means of the Laplace
transform method. State-selective mirrors are described in the limit of strong
lasers. The ladder, V and configurations for a three-level atom are
discussed. For the two level case, the transient effects arising as result of
the interaction between both a semi-infinite beam and a wavepacket with the
on-resonance laser are examined.Comment: 13 pages, 6 figure
Exclusive light particle measurements for the system F + C at 96 MeV
Decay sequence of hot {31}^P nucleus has been investigated through
exclusive light charged particle measurements in coincidence with individual
evaporation residues using the reaction {19}^F (96 MeV) + {12}^C.
Information on the sequential decay chain have been extracted by confronting
the data with the predictions of the statistical model. It is observed from the
present analysis that such exclusive light charged particle data may be used as
a powerful tool to probe the decay sequence of the hot light compound systems.Comment: 13 pages, 8 figures, Physical Review C (in press
On holographic dark-energy models
Different holographic dark-energy models are studied from a unifying point of
view. We compare models for which the Hubble scale, the future event horizon or
a quantity proportional to the Ricci scale are taken as the infrared cutoff
length. We demonstrate that the mere definition of the holographic dark-energy
density generally implies an interaction with the dark-matter component. We
discuss the relation between the equation-of-state parameter and the energy
density ratio of both components for each of the choices, as well as the
possibility of non-interacting and scaling solutions. Parameter estimations for
all three cutoff options are performed with the help of a Bayesian statistical
analysis, using data from supernovae type Ia and the history of the Hubble
parameter. The CDM model is the clear winner of the analysis.
According to the Bayesian Information Criterion (), all holographic models
should be considered as ruled out, since the difference to the
corresponding CDM value is . According to the Akaike Information
Criterion (), however, we find for models with
Hubble-scale and Ricci-scale cutoffs, indicating, that they may still be
competitive. As we show for the example of the Ricci-scale case, also the use
of certain priors, reducing the number of free parameters to that of the
CDM model, may result in a competitive holographic model.Comment: 37 pages, 11 figures, 3 tables, statistical analysis improved,
accepted for publication in Phys.Rev.
Adjuvants : an essential component of neisseria vaccines
Adjuvants may be classified into delivery systems and immune potentiator or modulator molecules based on their mechanism of action. Neisseria vaccines containing traditional adjuvants such as aluminium salts have existed for long time, but meningitis caused by Neisseria meningitidis serogroups, particularly serogroup B, continues to be a global health problem. Novel strategies have applied in silico and recombinant technologies to develop "universal" antigens (e.g. proteins, peptides and plasmid DNA) for vaccines, but these antigens have been shown to be poorly immunogenic even when alum adjuvanted, implying a need for better vaccine design. In this work we review the use of natural, detoxified, or synthetic molecules in combination with antigens to activate the innate immune system and to modulate the adaptive immune responses. In the main, antigenic and imune potentiator signals are delivered using nano-, micro-particles, alum, or emulsions. The importance of interaction between adjuvants and antigens to activate and target dendritic cells, the bridge between the innate and adaptive immune systems, will be discussed. In addition, nasal vaccine strategies based on the development of mucosal adjuvants and Neisseria derivatives to eliminate the pathogen at the site of infection provide promising adjuvants effective not only against respiratory pathogens, but also against pathogens responsible for enteric and sexually transmitted diseases
- …