310 research outputs found
Application of Pad\'{e} interpolation to stationary state problems
If the small and large coupling behavior of a physical system can be computed
perturbatively and expressed respectively as power series in a coupling
parameter and , a Pad\'{e} approximant embracing the two series can
interpolate between these two limits and provide an accurate estimate of the
system's behavior in the generally intractable intermediate coupling regime.
The methodology and validity of this approach are illustrated by considering
several stationary state problems in quantum mechanics.Comment: RevTeX4, 7 pages (including 7 tables); v4 typos correcte
How CMB and large-scale structure constrain chameleon interacting dark energy
We explore a chameleon type of interacting dark matter-dark energy scenario
in which a scalar field adiabatically traces the minimum of an effective
potential sourced by the dark matter density. We discuss extensively the effect
of this coupling on cosmological observables, especially the parameter
degeneracies expected to arise between the model parameters and other
cosmological parameters, and then test the model against observations of the
cosmic microwave background (CMB) anisotropies and other cosmological probes.
We find that the chameleon parameters and , which determine
respectively the slope of the scalar field potential and the dark matter-dark
energy coupling strength, can be constrained to and using CMB data alone. The latter parameter in particular is constrained
only by the late Integrated Sachs-Wolfe effect. Adding measurements of the
local Hubble expansion rate tightens the bound on by a factor of
two, although this apparent improvement is arguably an artefact of the tension
between the local measurement and the value inferred from Planck data in
the minimal CDM model. The same argument also precludes chameleon
models from mimicking a dark radiation component, despite a passing similarity
between the two scenarios in that they both delay the epoch of matter-radiation
equality. Based on the derived parameter constraints, we discuss possible
signatures of the model for ongoing and future large-scale structure surveys.Comment: 25 pages, 6 figure
Unparticle constraints from SN1987A
The existence of an unparticle sector, weakly coupled to the standard model,
would have a profound impact on supernova (SN) physics. Emission of energy into
the unparticle sector from the core of SN1987A would have significantly
shortened the observed neutrino burst. The unparticle interaction with
nucleons, neutrinos, electrons and muons is constrained to be so weak that it
is unlikely to provide any missing-energy signature at colliders. One important
exception are models where scale invariance in the hidden sector is broken by
the Higgs vacuum expectation value. In this case the SN emission is suppressed
by threshold effects.Comment: 4 pages, 1 figur
Boltzmann hierarchy for interacting neutrinos I: formalism
Starting from the collisional Boltzmann equation, we derive for the first
time and from first principles the Boltzmann hierarchy for neutrinos including
interactions with a scalar particle. Such interactions appear, for example, in
majoron-like models of neutrino mass generation. We study two limits of the
scalar mass: (i) An extremely massive scalar whose only role is to mediate an
effective 4-fermion neutrino-neutrino interaction, and (ii) a massless scalar
that can be produced in abundance and thus demands its own Boltzmann hierarchy.
In contrast to, e.g., the first-order Boltzmann hierarchy for
Thomson-scattering photons, our interacting neutrino/scalar Boltzmann
hierarchies contain additional momentum-dependent collision terms arising from
a non-negligible energy transfer in the neutrino-neutrino and neutrino-scalar
interactions. This necessitates that we track each momentum mode of the phase
space distributions individually, even if the particles were massless.
Comparing our hierarchy with the commonly used -parameterisation, we find no formal correspondence between the two
approaches, which raises the question of whether the latter parameterisation
even has an interpretation in terms of particle scattering. Lastly, although we
have invoked majoron-like models as a motivation for our study, our treatment
is in fact generally applicable to all scenarios in which the neutrino and/or
other ultrarelativistic fermions interact with scalar particles.Comment: 44 pages, 14 figures; included scalar Boltzmann hierarchy in the
massless case and plots of integral kernels; accepted by JCA
Getting leverage on inflation with a large photometric redshift survey
We assess the potential of a future large-volume photometric redshift survey
to constrain observational inflationary parameters using three large-scale
structure observables: the angular shear and galaxy power spectra, and the
cluster mass function measured through weak lensing. When used in combination
with Planck-like CMB measurements, we find that the spectral index n_s can be
constrained to a 1 sigma precision of up to 0.0025. The sensitivity to the
running of the spectral index can potentially improve to 0.0017, roughly a
factor of five better than the present 1 sigma~constraint from Planck and
auxiliary CMB data, allowing us to test the assumptions of the slow-roll
scenario with unprecedented accuracy. Interestingly, neither CMB+shear nor
CMB+galaxy nor CMB+clusters alone can achieve this level of sensitivity; it is
the combined power of all three probes that conspires to break the different
parameter degeneracies inherent in each type of observations. We make our
forecast software publicly available via download or upon request from the
authors.Comment: 22 pages, 6 figures; the forecast software can be downloaded from
http://jhamann.web.cern.ch/jhamann/simdata/simdata.tar.g
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