357 research outputs found
An Observational Test of Two-field Inflation
We study adiabatic and isocurvature perturbation spectra produced by a period
of cosmological inflation driven by two scalar fields. We show that there
exists a model-independent consistency condition for all two-field models of
slow-roll inflation, despite allowing for model-dependent linear processing of
curvature and isocurvature perturbations during and after inflation on
super-horizon scales. The scale-dependence of all spectra are determined solely
in terms of slow-roll parameters during inflation and the dimensionless
cross-correlation between curvature and isocurvature perturbations. We present
additional model-dependent consistency relations that may be derived in
specific two-field models, such as the curvaton scenario.Comment: 6 pages, latex with revtex, no figures; v2, minor changes, to appear
in Physical Review
Can inflationary models of cosmic perturbations evade the secondary oscillation test?
We consider the consequences of an observed Cosmic Microwave Background (CMB)
temperature anisotropy spectrum containing no secondary oscillations. While
such a spectrum is generally considered to be a robust signature of active
structure formation, we show that such a spectrum {\em can} be produced by
(very unusual) inflationary models or other passive evolution models. However,
we show that for all these passive models the characteristic oscillations would
show up in other observable spectra. Our work shows that when CMB polarization
and matter power spectra are taken into account secondary oscillations are
indeed a signature of even these very exotic passive models. We construct a
measure of the observability of secondary oscillations in a given experiment,
and show that even with foregrounds both the MAP and \pk satellites should be
able to distinguish between models with and without oscillations. Thus we
conclude that inflationary and other passive models can {\em not} evade the
secondary oscillation test.Comment: Final version accepted for publication in PRD. Minor improvements
have been made to the discussion and new data has been included. The
conclusions are unchagne
The Conservation Costs of Game Ranching
The devolution of user rights of wildlife in southern Africa has led to a widespread land-use shift from livestock farming to game ranching. The economic advantages of game ranching over livestock farming are significant, but so too are the risks associated with breeding financially valuable game where free-ranging wildlife pose a credible threat. Here, we assessed whether the conservation potential of game ranching, and a decentralized approach to conservation more generally, may be undermined by an increase in human-wildlife conflict. We demonstrate that game rancher tolerance towards free-ranging wildlife has significantly decreased as the game ranching industry has evolved. Our findings reveal a conflict of interest between wealth and wildlife conservation resulting from local decision-making in the absence of adequate centralized governance and evidence-based best practice. As a fundamental pillar of devolution-based natural resource management, game ranching proves an important mechanism for economic growth, albeit at a significant cost to conservation
Electroactive biofilms: new means for electrochemistry
This work demonstrates that electrochemical reactions can be catalysed by the natural biofilms that form on
electrode surfaces dipping into drinking water or compost. In drinking water, oxygen reduction was monitored with
stainless steel ultra-microelectrodes under constant potential electrolysis at )0.30 V/SCE for 13 days. 16 independent experiments were conducted in drinking water, either pure or with the addition of acetate or dextrose. In
most cases, the current increased and reached 1.5–9.5 times the initial current. The current increase was attributed to
biofilm forming on the electrode in a similar way to that has been observed in seawater. Epifluorescence microscopy
showed that the bacteria size and the biofilm morphology depended on the nutrients added, but no quantitative
correlation between biofilm morphology and current was established. In compost, the oxidation process was
investigated using a titanium based electrode under constant polarisation in the range 0.10–0.70 V/SCE. It was
demonstrated that the indigenous micro-organisms were responsible for the current increase observed after a few
days, up to 60 mA m)2. Adding 10 mM acetate to the compost amplified the current density to 145 mA m)2 at 0.50 V/SCE. The study suggests that many natural environments, other than marine sediments, waste waters and
seawaters that have been predominantly investigated until now, may be able to produce electrochemically active
biofilm
Bounds from Primordial Black Holes with a Near Critical Collapse Initial Mass Function
Recent numerical evidence suggests that a mass spectrum of primordial black
holes (PBHs) is produced as a consequence of near critical gravitational
collapse. Assuming that these holes formed from the initial density
perturbations seeded by inflation, we calculate model independent upper bounds
on the mass variance at the reheating temperature by requiring the mass density
not exceed the critical density and the photon emission not exceed current
diffuse gamma-ray measurements. We then translate these results into bounds on
the spectral index n by utilizing the COBE data to normalize the mass variance
at large scales, assuming a constant power law, then scaling this result to the
reheating temperature. We find that our bounds on n differ substantially
(\delta n > 0.05) from those calculated using initial mass functions derived
under the assumption that the black hole mass is proportional to the horizon
mass at the collapse epoch. We also find a change in the shape of the diffuse
gamma-ray spectrum which results from the Hawking radiation. Finally, we study
the impact of a nonzero cosmological constant and find that the bounds on n are
strengthened considerably if the universe is indeed vacuum-energy dominated
today.Comment: 24 pages, REVTeX, 5 figures; minor typos fixed, two refs added,
version to be published in PR
Signatures of Relativistic Neutrinos in CMB Anisotropy and Matter Clustering
We present a detailed analytical study of ultra-relativistic neutrinos in
cosmological perturbation theory and of the observable signatures of
inhomogeneities in the cosmic neutrino background. We note that a modification
of perturbation variables that removes all the time derivatives of scalar
gravitational potentials from the dynamical equations simplifies their solution
notably. The used perturbations of particle number per coordinate, not proper,
volume are generally constant on superhorizon scales. In real space an
analytical analysis can be extended beyond fluids to neutrinos.
The faster cosmological expansion due to the neutrino background changes the
acoustic and damping angular scales of the cosmic microwave background (CMB).
But we find that equivalent changes can be produced by varying other standard
parameters, including the primordial helium abundance. The low-l integrated
Sachs-Wolfe effect is also not sensitive to neutrinos. However, the gravity of
neutrino perturbations suppresses the CMB acoustic peaks for the multipoles
with l>~200 while it enhances the amplitude of matter fluctuations on these
scales. In addition, the perturbations of relativistic neutrinos generate a
*unique phase shift* of the CMB acoustic oscillations that for adiabatic
initial conditions cannot be caused by any other standard physics. The origin
of the shift is traced to neutrino free-streaming velocity exceeding the sound
speed of the photon-baryon plasma. We find that from a high resolution, low
noise instrument such as CMBPOL the effective number of light neutrino species
can be determined with an accuracy of sigma(N_nu) = 0.05 to 0.09, depending on
the constraints on the helium abundance.Comment: 38 pages, 7 figures. Version accepted for publication in PR
Hubble expansion and structure formation in the "running FLRW model" of the cosmic evolution
A new class of FLRW cosmological models with time-evolving fundamental
parameters should emerge naturally from a description of the expansion of the
universe based on the first principles of quantum field theory and string
theory. Within this general paradigm, one expects that both the gravitational
Newton's coupling, G, and the cosmological term, Lambda, should not be strictly
constant but appear rather as smooth functions of the Hubble rate. This
scenario ("running FLRW model") predicts, in a natural way, the existence of
dynamical dark energy without invoking the participation of extraneous scalar
fields. In this paper, we perform a detailed study of these models in the light
of the latest cosmological data, which serves to illustrate the
phenomenological viability of the new dark energy paradigm as a serious
alternative to the traditional scalar field approaches. By performing a joint
likelihood analysis of the recent SNIa data, the CMB shift parameter, and the
BAOs traced by the Sloan Digital Sky Survey, we put tight constraints on the
main cosmological parameters. Furthermore, we derive the theoretically
predicted dark-matter halo mass function and the corresponding redshift
distribution of cluster-size halos for the "running" models studied. Despite
the fact that these models closely reproduce the standard LCDM Hubble
expansion, their normalization of the perturbation's power-spectrum varies,
imposing, in many cases, a significantly different cluster-size halo redshift
distribution. This fact indicates that it should be relatively easy to
distinguish between the "running" models and the LCDM cosmology using realistic
future X-ray and Sunyaev-Zeldovich cluster surveys.Comment: Version published in JCAP 08 (2011) 007: 1+41 pages, 6 Figures, 1
Table. Typos corrected. Extended discussion on the computation of the
linearly extrapolated density threshold above which structures collapse in
time-varying vacuum models. One appendix, a few references and one figure
adde
Neutrino masses: From fantasy to facts
Theory suggests the existence of neutrino masses, but little more. Facts are
coming close to reveal our fantasy: solar and atmospheric neutrino data
strongly indicate the need for neutrino conversions, while LSND provides an
intriguing hint. The simplest ways to reconcile these data in terms of neutrino
oscillations invoke a light sterile neutrino in addition to the three active
ones. Out of the four neutrinos, two are maximally-mixed and lie at the LSND
scale, while the others are at the solar mass scale. These schemes can be
distinguished at neutral-current-sensitive solar & atmospheric neutrino
experiments. I discuss the simplest theoretical scenarios, where the lightness
of the sterile neutrino, the nearly maximal atmospheric neutrino mixing, and
the generation of & all follow
naturally from the assumed lepton-number symmetry and its breaking. Although
the most likely interpretation of the present data is in terms of
neutrino-mass-induced oscillations, one still has room for alternative
explanations, such as flavour changing neutrino interactions, with no need for
neutrino mass or mixing. Such flavour violating transitions arise in theories
with strictly massless neutrinos, and may lead to other sizeable flavour
non-conservation effects, such as , conversion in
nuclei, unaccompanied by neutrino-less double beta decay.Comment: 33 pages, latex, 16 figures. Invited Talk at Ioannina Conference,
Symmetries in Intermediate High Energy Physics and its Applications, Oct.
1998, to be published by Springer Tracts in Modern Physics. Festschrift in
Honour of John Vergados' 60th Birthda
Professionalism, Golf Coaching and a Master of Science Degree: A commentary
As a point of reference I congratulate Simon Jenkins on tackling the issue of professionalism in coaching. As he points out coaching is not a profession, but this does not mean that coaching would not benefit from going through a professionalization process. As things stand I find that the stimulus article unpacks some critically important issues of professionalism, broadly within the context of golf coaching. However, I am not sure enough is made of understanding what professional (golf) coaching actually is nor how the development of a professional golf coach can be facilitated by a Master of Science Degree (M.Sc.). I will focus my commentary on these two issues
Does accelerating universe indicates Brans-Dicke theory
The evolution of universe in Brans-Dicke (BD) theory is discussed in this
paper.
Considering a parameterized scenario for BD scalar field
which plays the role of gravitational "constant" ,
we apply the Markov Chain Monte Carlo method to investigate a global
constraints on BD theory with a self-interacting potential according to the
current observational data: Union2 dataset of type supernovae Ia (SNIa),
high-redshift Gamma-Ray Bursts (GRBs) data, observational Hubble data (OHD),
the cluster X-ray gas mass fraction, the baryon acoustic oscillation (BAO), and
the cosmic microwave background (CMB) data. It is shown that an expanded
universe from deceleration to acceleration is given in this theory, and the
constraint results of dimensionless matter density and parameter
are, and
which is consistent with the
result of current experiment exploration, . In
addition, we use the geometrical diagnostic method, jerk parameter , to
distinguish the BD theory and cosmological constant model in Einstein's theory
of general relativity.Comment: 16 pages, 3 figure
- …