4,640 research outputs found
Relaxing a large cosmological constant in the astrophysical domain
We study the problem of relaxing a large cosmological constant in the
astrophysical domain through a dynamical mechanism based on a modified action
of gravity previously considered by us at the cosmological level. We solve the
model in the Schwarzschild-de Sitter metric for large and small astrophysical
scales, and address its physical interpretation by separately studying the
Jordan's frame and Einstein's frame formulations of it. In particular, we
determine the extremely weak strength of fifth forces in our model and show
that they are virtually unobservable. Finally, we estimate the influence that
the relaxation mechanism may have on pulling apart the values of the two
gravitational potentials Psi and Phi of the metric, as this implies a departure
of the model from General Relativity and could eventually provide an
observational test of the new framework at large astrophysical scales, e.g.
through gravitational lensing.Comment: 14 pages, 3 figures, accepted in Mod. Phys. Lett. A, extended
discussion, references adde
SIC~POVMs and Clifford groups in prime dimensions
We show that in prime dimensions not equal to three, each group covariant
symmetric informationally complete positive operator valued measure (SIC~POVM)
is covariant with respect to a unique Heisenberg--Weyl (HW) group. Moreover,
the symmetry group of the SIC~POVM is a subgroup of the Clifford group. Hence,
two SIC~POVMs covariant with respect to the HW group are unitarily or
antiunitarily equivalent if and only if they are on the same orbit of the
extended Clifford group. In dimension three, each group covariant SIC~POVM may
be covariant with respect to three or nine HW groups, and the symmetry group of
the SIC~POVM is a subgroup of at least one of the Clifford groups of these HW
groups respectively. There may exist two or three orbits of equivalent
SIC~POVMs for each group covariant SIC~POVM, depending on the order of its
symmetry group. We then establish a complete equivalence relation among group
covariant SIC~POVMs in dimension three, and classify inequivalent ones
according to the geometric phases associated with fiducial vectors. Finally, we
uncover additional SIC~POVMs by regrouping of the fiducial vectors from
different SIC~POVMs which may or may not be on the same orbit of the extended
Clifford group.Comment: 30 pages, 1 figure, section 4 revised and extended, published in J.
Phys. A: Math. Theor. 43, 305305 (2010
Aspects of power corrections in hadron-hadron collisions
The program of understanding inverse-power law corrections to event shapes
and energy flow observables in e+ e- annihilation to two jets and DIS (1+1)
jets has been a significant success of QCD phenomenology over the last decade.
The important extension of this program to similar observables in hadron
collisions is not straightforward, being obscured by both conceptual and
technical issues. In this paper we shed light on some of these issues by
providing an estimate of power corrections to the inter-jet E_t flow
distribution in hadron collisions using the techniques that were employed in
the e+ e- annihilation and DIS cases.Comment: 15 pages, 1 figure, uses JHEP3.cl
On the dynamic tensile strength of Zirconium
Despite its fundamental nature, the process of dynamic tensile failure (spall) is poorly understood. Spall initiation via cracks, voids, etc, before subsequent coalesce, is known to be highly microstructure-dependant. In particular, the availability of slip planes and other methods of plastic deformation controls the onset (or lack thereof) of spall. While studies have been undertaken into the spall response of BCC and FCC materials, less attention has paid to the spall response of highly anisotropic HCP materials. Here the dynamic behaviour of zirconium is investigated via plate-impact experiments, with the aim of building on an ongoing in-house body of work investigating these highly complex materials. In particular, in this paper the effect of impact stress on spall in a commercially sourced Zr rod is considered, with apparent strain-rate softening highlighted
Mutually unbiased bases: tomography of spin states and star-product scheme
Mutually unbiased bases (MUBs) are considered within the framework of a
generic star-product scheme. We rederive that a full set of MUBs is adequate
for a spin tomography, i.e. knowledge of all probabilities to find a system in
each MUB-state is enough for a state reconstruction. Extending the ideas of the
tomographic-probability representation and the star-product scheme to
MUB-tomography, dequantizer and quantizer operators for MUB-symbols of spin
states and operators are introduced, ordinary and dual star-product kernels are
found. Since MUB-projectors are to obey specific rules of the star-product
scheme, we reveal the Lie algebraic structure of MUB-projectors and derive new
relations on triple- and four-products of MUB-projectors. Example of qubits is
considered in detail. MUB-tomography by means of Stern-Gerlach apparatus is
discussed.Comment: 11 pages, 1 table, partially presented at the 17th Central European
Workshop on Quantum Optics (CEWQO'2010), June 6-11, 2010, St. Andrews,
Scotland, U
CONTEMPORARY CHALLENGES FACING THE AUSTRALIAN JUDICIARY: AN EMPIRICAL INTERRUPTION
© 2019 Melbourne University Law Review. All rights reserved. The structures that regulate and support the Australian judiciary reflect and serve the traditional judicial values of independence, impartiality and the rule of law. Yet modern society places emphasis on an additional range of values that are expected of government and public institutions. These contemporary values include diversity, transparency, accountability and efficiency. Reforms to introduce regulatory and support structures that prioritise and facilitate these values in the judicial arm has proved challenging and, sometimes, contentious. This article reports on a survey of Australian judicial officers (n = 142) from across different jurisdictions. Participants were asked what they considered to be the most pressing challenges that face the various levels of the Australian judiciary, and whether the current regulatory and support environment achieves international best practice. The responses provide a nuanced picture of the state of the modern Australian judiciary as it appears to those within it. The study facilitates an understanding of the degree to which judicial officers are satisfied with the current legal and regulatory framework and, where they are dissatisfied, the nature of their disquiet. While not seeking to offer complete resolutions to the many issues canvassed, the data and analysis presented in this article serve as an interruption to regulatory and academic studies of the Australian judiciary, with the potential to illuminate and re-orientate the reform conversation in light of the judicial perspective on these various issues
Parameterizing scalar-tensor theories for cosmological probes
We study the evolution of density perturbations for a class of models
which closely mimic CDM background cosmology. Using the quasi-static
approximation, and the fact that these models are equivalent to scalar-tensor
gravity, we write the modified Friedmann and cosmological perturbation
equations in terms of the mass of the scalar field. Using the perturbation
equations, we then derive an analytic expression for the growth parameter
in terms of , and use our result to reconstruct the linear matter
power spectrum. We find that the power spectrum at is characterized
by a tilt relative to its General Relativistic form, with increased power on
small scales. We discuss how one has to modify the standard, constant
prescription in order to study structure formation for this class of models.
Since is now scale and time dependent, both the amplitude and transfer
function associated with the linear matter power spectrum will be modified. We
suggest a simple parameterization for the mass of the scalar field, which
allows us to calculate the matter power spectrum for a broad class of
models
Retrodictively Optimal Localisations in Phase Space
In a previous paper it was shown that the distribution of measured values for
a retrodictively optimal simultaneous measurement of position and momentum is
always given by the initial state Husimi function. This result is now
generalised to retrodictively optimal simultaneous measurements of an arbitrary
pair of rotated quadratures x_theta1 and x_theta2. It is shown, that given any
such measurement, it is possible to find another such measurement,
informationally equivalent to the first, for which the axes defined by the two
quadratures are perpendicular. It is further shown that the distribution of
measured values for such a meaurement belongs to the class of generalised
Husimi functions most recently discussed by Wuensche and Buzek. The class
consists of the subset of Wodkiewicz's operational probability distributions
for which the filter reference state is a squeezed vaccuum state.Comment: 11 pages, 2 figures. AMS Latex. Replaced with published versio
On analytical solutions of f(R) modified gravity theories in FLRW cosmologies
A novel analytical method for f(R) modified theories without matter in
Friedmann-Lemaitre-Robertson-Walker spacetimes is introduced. The equation of
motion for the scale factor in terms of cosmic time is reduced to the equation
for the evolution of the Ricci scalar R with the Hubble parameter H. The
solution of equation of motion for actions of the form of power law in Ricci
scalar R, is presented with a detailed elaboration of the action quadratic in
R. The reverse use of the introduced method is exemplified in finding
functional forms f(R) which lead to specified scale factor functions. The
analytical solutions are corroborated by numerical calculations with excellent
agreement. Possible further applications to the phases of inflationary
expansion and late-time acceleration as well as f(R) theories with radiation
are outlined.Comment: 16 pages, 6 figures. v2: minor changes, references added. v3: minor
changes, more references added. v4: version to appear in IJMPD. v5: DOI and
journal reference adde
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