7,651 research outputs found
Theory of controlled quantum dynamics
We introduce a general formalism, based on the stochastic formulation of
quantum mechanics, to obtain localized quasi-classical wave packets as
dynamically controlled systems, for arbitrary anharmonic potentials. The
control is in general linear, and it amounts to introduce additional quadratic
and linear time-dependent terms to the given potential. In this way one can
construct for general systems either coherent packets moving with constant
dispersion, or dynamically squeezed packets whose spreading remains bounded for
all times. In the standard operatorial framework our scheme corresponds to a
suitable generalization of the displacement and scaling operators that generate
the coherent and squeezed states of the harmonic oscillator.Comment: LaTeX, A4wide, 28 pages, no figures. To appear in J. Phys. A: Math.
Gen., April 199
IGR J14257-6117, a magnetic accreting white dwarf with a very strong X-ray orbital modulation
IGR J14257-6117 is an unclassified source in the hard X-ray catalogues.
Optical follow-ups suggest it could be a Cataclysmic Variable of the magnetic
type. We present the first high S/N X-ray observation performed by \XMM\ at
0.3--10 keV, complemented with 10--80 keV coverage by \Swift/BAT, aimed at
revealing the source nature. We detected for the first time a fast periodic
variability at 509.5\,s and a longer periodic variability at 4.05\,h, ascribed
to the white dwarf (WD) spin and binary orbital periods, respectively. These
unambiguously identify IGR J14257-6117 as a magnetic CV of the Intermediate
Polar (IP) type. The energy resolved light curves at both periods reveal
amplitudes decreasing with increasing energy, with the orbital modulation
reaching in the softest band. The energy spectrum shows optically
thin thermal emission with an excess at the iron complex, absorbed by two dense
media (), partially covering the X-ray
source. These are likely localised in the magnetically confined accretion flow
above the WD surface and at the disc rim, producing the energy dependent spin
and orbital variabilities, respectively. IGR J14257-6117, joins the group of
strongest orbitally modulated IPs now counting four systems. Drawing
similarities with low-mass X-ray binaries displaying orbital dips, these IPs
should be seen at large orbital inclinations allowing azimuthally extended
absorbing material fixed in the binary frame to intercept the line of sight.
For IGR J14257-6117, we estimate (). Whether
also the mass accretion rate plays a role in the large orbital modulations in
IPs cannot be established with the present data.Comment: Accepted for publication on MNRAS. 9 pages, 6 table, 5 figure
Constraining f(R) gravity with PLANCK data on galaxy cluster profiles
Models of gravity that introduce corrections to the Newtonian
potential in the weak field limit are tested at the scale of galaxy clusters.
These models can explain the dynamics of spiral and elliptical galaxies without
resorting to dark matter. We compute the pressure profiles of 579 galaxy
clusters assuming that the gas is in hydrostatic equilibrium within the
potential well of the modified gravitational field. The predicted profiles are
compared with the average profile obtained by stacking the data of our cluster
sample in the Planck foreground clean map SMICA. We find that the resulting
profiles of these systems fit the data without requiring a dominant dark matter
component, with model parameters similar to those required to explain the
dynamics of galaxies. Our results do not rule out that clusters are dynamically
dominated by Dark Matter but support the idea that Extended Theories of Gravity
could provide an explanation to the dynamics of self-gravitating systems and to
the present period of accelerated expansion, alternative to the concordance
cosmological model.Comment: 10 pages, 5 figures, accepted for publication in MNRA
ESR theory for interacting 1D quantum wires
We compute the electron spin resonance (ESR) intensity for one-dimensional
quantum wires in semiconductor heterostructures, taking into account
electron-electron interactions and spin-orbit coupling. The ESR spectrum is
shown to be very sensitive to interactions. While in the absence of
interactions, the spectrum is a flat band, characteristic threshold
singularities appear in the interacting limit. This suggests the practical use
of ESR to reveal spin dynamics in a Luttinger liquid.Comment: 7 pages, 2 figures. To be published in Europhys. Let
On the strategy frequency problem in batch Minority Games
Ergodic stationary states of Minority Games with S strategies per agent can
be characterised in terms of the asymptotic probabilities with which
an agent uses of his strategies. We propose here a simple and general
method to calculate these quantities in batch canonical and grand-canonical
models. Known analytic theories are easily recovered as limiting cases and, as
a further application, the strategy frequency problem for the batch
grand-canonical Minority Game with S=2 is solved. The generalization of these
ideas to multi-asset models is also presented. Though similarly based on
response function techniques, our approach is alternative to the one recently
employed by Shayeghi and Coolen for canonical batch Minority Games with
arbitrary number of strategies.Comment: 17 page
On the transition to efficiency in Minority Games
The existence of a phase transition with diverging susceptibility in batch
Minority Games (MGs) is the mark of informationally efficient regimes and is
linked to the specifics of the agents' learning rules. Here we study how the
standard scenario is affected in a mixed population game in which agents with
the `optimal' learning rule (i.e. the one leading to efficiency) coexist with
ones whose adaptive dynamics is sub-optimal. Our generic finding is that any
non-vanishing intensive fraction of optimal agents guarantees the existence of
an efficient phase. Specifically, we calculate the dependence of the critical
point on the fraction of `optimal' agents focusing our analysis on three
cases: MGs with market impact correction, grand-canonical MGs and MGs with
heterogeneous comfort levels.Comment: 12 pages, 3 figures; contribution to the special issue "Viewing the
World through Spin Glasses" in honour of David Sherrington on the occasion of
his 65th birthda
Adaptive drivers in a model of urban traffic
We introduce a simple lattice model of traffic flow in a city where drivers
optimize their route-selection in time in order to avoid traffic jams, and
study its phase structure as a function of the density of vehicles and of the
drivers' behavioral parameters via numerical simulations and mean-field
analytical arguments. We identify a phase transition between a low- and a
high-density regime. In the latter, inductive drivers may surprisingly behave
worse than randomly selecting drivers.Comment: 7 pages, final versio
Swift J0525.6+2416 and IGR J04571+4527: two new hard X-ray selected magnetic cataclysmic variables identified with XMM-Newton
IGR J04571+4527 and Swift J0525.6+2416 are two hard X-ray sources detected in
the Swift/BAT and INTEGRAL/IBIS surveys. They were proposed to be magnetic
cataclysmic variables of the Intermediate Polar (IP) type, based on optical
spectroscopy. IGR J04571+4527 also showed a 1218 s optical periodicity,
suggestive of the rotational period of a white dwarf, further pointing towards
an IP classification. We here present detailed X-ray (0.3-10 keV) timing and
spectral analysis performed with XMM-Newton, complemented with hard X-ray
coverage (15-70 keV) from Swift/BAT. These are the first high signal to noise
observations in the soft X-ray domain for both sources, allowing us to identify
the white dwarf X-ray spin period of Swift J0525.6+2416 (226.28 s), and IGR
J04571+4527 (1222.6 s). A model consisting of multi-temperature optically thin
emission with complex absorption adequately fits the broad-band spectrum of
both sources. We estimate a white dwarf mass of about 1.1 and 1.0 solar masses
for IGR J04571+4527 and Swift J0525.6+2416, respectively. The above
characteristics allow us to unambiguously classify both sources as IPs,
confirming the high incidence of this subclass among hard X-ray emitting
Cataclysmic Variables.Comment: 8 pages, 4 figures, 3 tables. Accepted for publication in MNRA
Magnetic Cataclysmic Variables discovered in hard X-rays
Among hard X-ray galactic sources detected by INTEGRAL and Swift surveys,
those discovered as accreting white dwarfs have surprisingly boosted in number,
representing 20% of the galactic sample. The majority are identified as
magnetic cataclysmic variabiles of the intermediate polar type suggesting this
subclass as an important constituent of galactic population of X-ray sources.
In this conference-proceeding, we review the X-ray emission properties as
observed with our ongoing XMM-Newton programme of newly discovered INTEGRAL
and/or Swift sources that enlarged almost by a factor of two, identifying
cataclysmic variabiles commonalities and outliers.Comment: Proceedings of the 12th INTEGRAL conference and 1st AHEAD Gamma-ray
Workshop, Geneva (Switzerland), 11-15 February 2019, Ed. C. Ferrigno, E.
Bozzo, P. von Balmoos
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