296 research outputs found
A revision of the Generalized Uncertainty Principle
The Generalized Uncertainty Principle arises from the Heisenberg Uncertainty
Principle when gravity is taken into account, so the leading order correction
to the standard formula is expected to be proportional to the gravitational
constant . On the other hand, the emerging picture suggests a
set of departures from the standard theory which demand a revision of all the
arguments used to deduce heuristically the new rule. In particular, one can now
argue that the leading order correction to the Heisenberg Uncertainty Principle
is proportional to the first power of the Planck length . If so, the
departures from ordinary quantum mechanics would be much less suppressed than
what is commonly thought.Comment: 6 pages, 1 figur
On the modification of Hamiltonians' spectrum in gravitational quantum mechanics
Different candidates of Quantum Gravity such as String Theory, Doubly Special
Relativity, Loop Quantum Gravity and black hole physics all predict the
existence of a minimum observable length or a maximum observable momentum which
modifies the Heisenberg uncertainty principle. This modified version is usually
called the Generalized (Gravitational) Uncertainty Principle (GUP) and changes
all Hamiltonians in quantum mechanics. In this Letter, we use a recently
proposed GUP which is consistent with String Theory, Doubly Special Relativity
and black hole physics and predicts both a minimum measurable length and a
maximum measurable momentum. This form of GUP results in two additional terms
in any quantum mechanical Hamiltonian, proportional to and
, respectively, where is the GUP
parameter. By considering both terms as perturbations, we study two quantum
mechanical systems in the framework of the proposed GUP: a particle in a box
and a simple harmonic oscillator. We demonstrate that, for the general
polynomial potentials, the corrections to the highly excited eigenenergies are
proportional to their square values. We show that this result is exact for the
case of a particle in a box.Comment: 11 pages, to appear in Europhysics Letter
Brane Cosmology and KK Gravitinos
The cosmology of KK gravitinos in models with extra dimensions is considered.
The main result is that the production of such KK modes is not compatible with
an epoch of non--standard expansion after inflation. This is so because the BBN
constraint on the zero mode forces the reduced five dimensional Planck mass
down to values much smaller than the usual four dimensional one, but this
in turn implies many KK states available for a given temperature. Once these
states are taken into account one finds that there is no for which the
produced KK gravitinos satisfy BBN and overclosure constraints. This conclusion
holds for both flat and warped models in which only gravity propagates in the
full spacetime.Comment: 19 pages, references added, IoP styl
Testing the performance and accuracy of the RELXILL model for the relativistic X-ray reflection from accretion disks
The reflection spectroscopic model RELXILL is commonly implemented in
studying relativistic X-ray reflection from accretion disks around black holes.
We present a systematic study of the model's capability to constrain the
dimensionless spin and ionization parameters from 6,000 NuSTAR
simulations of a bright X-ray source employing the lamppost geometry. We employ
high count spectra to show the limitations in the model without being confused
with limitations in signal-to-noise. We find that both parameters are
well-recovered at 90% confidence with improving constraints at higher
reflection fraction, high spin, and low source height. We test spectra across a
broad range - first at 1010 and then 10 total source counts
across the effective 3-79 keV band of NuSTAR, and discover a strong dependence
of the results on how fits are performed around the starting parameters, owing
to the complexity of the model itself. A blind fit chosen over an approach that
carries some estimates of the actual parameter values can lead to significantly
worse recovery of model parameters. We further stress on the importance to span
the space of nonlinear-behaving parameters like carefully and
thoroughly for the model to avoid misleading results. In light of selecting
fitting procedures, we recall the necessity to pay attention to the choice of
data binning and fit statistics used to test the goodness of fit by
demonstrating the effect on the photon index . We re-emphasize and
implore the need to account for the detector resolution while binning X-ray
data and using Poisson fit statistics instead while analyzing Poissonian data.Comment: 9 pages, 6 figures, accepted for publication in Ap
Asymmetric Properties of Heat Conduction in a One-Dimensional Frenkel-Kontorova Model
In this Letter, we show numerically that the rectifying effect of heat flux
in a one-dimensional two-segment Frenkel-Kontorova chain demonstrated in recent
literature is merely available under the limit of the weak coupling between the
two constituent segments. Surprisingly, the rectifying effect will be reversed
when the properties of the interface and the system size change. The two types
of asymmetric heat conduction are dominated by different mechanisms, which are
all induced by the nonlinearity. We further discuss the possibility of the
experimental realization of thermal diode or rectifier devices.Comment: 4 Pages, 4 figure
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