355 research outputs found
Dynamical dark energy and variation of fundamental "constants"
In this thesis we study the influence of a possible variation of fundamental
"constants" on the process of Big Bang Nucleosynthesis (BBN). Our findings are
combined with further studies on variations of constants in other physical
processes to constrain models of grand unification (GUT) and quintessence. We
will find that the 7Li problem of BBN can be ameliorated if one allows for
varying constants, where especially varying light quark masses show a strong
influence. Furthermore, we show that recent studies of varying constants are in
contradiction with each other and BBN in the framework of six exemplary GUT
scenarios, if one assumes monotonic variation with time. We conclude that there
is strong tension between recent claims of varying constants, hence either some
claims have to be revised, or there are much more sophisticated GUT relations
(and/or non-monotonic variations) realized in nature. The methods introduced in
this thesis prove to be powerful tools to probe regimes well beyond the
Standard Model of particle physics or the concordance model of cosmology, which
are currently inaccessible by experiments. Once the first irrefutable proofs of
varying constants are available, our method will allow for probing the
consistency of models beyond the standard theories like GUT or quintessence and
also the compatibility between these models.Comment: PhD thesis (University of Heidelberg, November 2008), 131 page
Competing bounds on the present-day time variation of fundamental constants
We compare the sensitivity of a recent bound on time variation of the fine
structure constant from optical clocks with bounds on time varying fundamental
constants from atomic clocks sensitive to the electron-to-proton mass ratio,
from radioactive decay rates in meteorites, and from the Oklo natural reactor.
Tests of the Weak Equivalence Principle also lead to comparable bounds on
present variations of constants. The "winner in sensitivity" depends on what
relations exist between the variations of different couplings in the standard
model of particle physics, which may arise from the unification of gauge
interactions. WEP tests are currently the most sensitive within unified
scenarios. A detection of time variation in atomic clocks would favour
dynamical dark energy and put strong constraints on the dynamics of a
cosmological scalar field.Comment: ~4 Phys Rev page
Primordial nucleosynthesis as a probe of fundamental physics parameters
We analyze the effect of variation of fundamental couplings and mass scales
on primordial nucleosynthesis in a systematic way. The first step establishes
the response of primordial element abundances to the variation of a large
number of nuclear physics parameters, including nuclear binding energies. We
find a strong influence of the n-p mass difference (for the 4He abundance), of
the nucleon mass (for deuterium) and of A=3,4,7 binding energies (for 3He, 6Li
and 7Li). A second step relates the nuclear parameters to the parameters of the
Standard Model of particle physics. The deuterium, and, above all, 7Li
abundances depend strongly on the average light quark mass hat{m} \equiv
(m_u+m_d)/2. We calculate the behaviour of abundances when variations of
fundamental parameters obey relations arising from grand unification. We also
discuss the possibility of a substantial shift in the lithium abundance while
the deuterium and 4He abundances are only weakly affected.Comment: v2: 34 pages, 2 figures, typo in last GUT scenario corrected, added
discussion and graph of nonlinear behaviour in GUT scenarios, added short
section discussing binding of dineutron and 8Be, refs added, conclusions
unaltered. Accepted for publication, Phys. Rev.
Thermally Assisted Spin Hall Effect
The spin polarized charge transport is systematically analyzed as a thermally
driven stochastic process. The approach is based on Kramers' equation
describing the semiclassical motion under the inclusion of stochastic and
damping forces. Due to the relativistic spin-orbit coupling the damping
experiences a relativistic correction leading to an additional contribution
within the spin Hall conductivity. A further contribution to the conductivity
is originated from the averaged underlying crystal potential, the mean value of
which depends significantly on the electric field. We derive an exact
expression for the electrical conductivity. All corrections are estimated in
lowest order of a relativistic approach and in the linear response regime.Comment: 12 pages, 1 figur
Advances in risk assessment for climate change adaptation policy
This is the author accepted manuscript. The final version is available from the publisher via the DOI in this recordClimate change risk assessment involves formal analysis of the consequences, likelihoods and responses to the impacts of climate change and the options for addressing these under societal constraints. Conventional approaches to risk assessment are challenged by the significant temporal and spatial dynamics of climate change; by the amplification of risks through societal preferences and values; and through the interaction of multiple risk factors. This paper introduces the theme issue by reviewing the current practice and frontiers of climate change risk assessment, with specific emphasis on the development of adaptation policy that aims to manage those risks. These frontiers include integrated assessments, dealing with climate risks across borders and scales, addressing systemic risks, and innovative co-production methods to prioritize solutions to climate challenges with decision-makers. By reviewing recent developments in the use of large-scale risk assessment for adaptation policy-making, we suggest a forward-looking research agenda to meet ongoing strategic policy requirements in local, national and international contexts. This article is part of the theme issue ‘Advances in risk assessment for climate change adaptation policy’.The authors acknowledge support from the UK Department for Environment, Food and Rural Affairs
in the preparation of the International Dimensions Assessment of the UK Climate Change Risk Assessment.
W.N.A. acknowledges support from High-end Climate Impacts and Extremes project of the EU. S.S. would
like to acknowledge the financial support of Ireland’s Environmental Protection Agency (EPA) under the
EPA Research Programme 2014–2020, of the UK Economic and Social Research Council (ESRC) through the
Centre for Climate Change Economics and Policy, and of the Grantham Foundation for the Protection of the
Environment through the Grantham Research Institute on Climate Change and the Environment
Unifying cosmological and recent time variations of fundamental couplings
A number of positive and null results on the time variation of fundamental
constants have been reported. It is difficult to judge whether or not these
claims are mutually consistent, since the observable quantities depend on
several parameters, namely the coupling strengths and masses of particles. The
evolution of these coupling-parameters over cosmological history is also a
priori unknown. A direct comparison requires a relation between the couplings.
We explore several distinct scenarios based on unification of gauge couplings,
providing a representative (though not exhaustive) sample of such relations.
For each scenario we obtain a characteristic time dependence and discuss
whether a monotonic time evolution is allowed. For all scenarios, some
contradictions between different observations appear. We show how a clear
observational determination of non-zero variations would test the dominant
mechanism of varying couplings within unified theories.Comment: Formatting changes and minor typos, equivalent to published version.
35 pages (11pt article format), 8 figure
Time variation of fundamental couplings and dynamical dark energy
Scalar field dynamics may give rise to a nonzero cosmological variation of
fundamental constants. Within different scenarios based on the unification of
gauge couplings, the various claimed observations and bounds may be combined in
order to trace or restrict the time history of the couplings and masses. If the
scalar field is responsible for a dynamical dark energy or quintessence,
cosmological information becomes available for its time evolution. Combining
this information with the time variation of couplings, one can determine the
interaction strength between the scalar and atoms, which may be observed by
tests of the Weak Equivalence Principle. We compute bounds on the present rate
of coupling variation from experiments testing the differential accelerations
for bodies with equal mass and different composition and compare the
sensitivity of various methods. In particular, we discuss two specific models
of scalar evolution: crossover quintessence and growing neutrino models.Comment: 26 pages, 2 figures; minor typos & added references, to be published
in JCA
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Zweitveröffentlichun
Big bang nucleosynthesis as a probe of fundamental "constants"
Big Bang nucleosynthesis (BBN) is the earliest sensitive probe of the values
of many fundamental particle physics parameters. We have found the leading
linear dependences of primordial abundances on all relevant parameters of the
standard BBN code, including binding energies and nuclear reaction rates. This
enables us to set limits on possible variations of fundamental parameters. We
find that 7Li is expected to be significantly more sensitive than other species
to many fundamental parameters, a result which also holds for variations of
coupling strengths in grand unified (GUT) models. Our work also indicates which
areas of nuclear theory need further development if the values of ``constants''
are to be more accurately probed.Comment: Refereed article to be published in Nuclear Physics in Astrophysics
III Proceedings, J. Phys. G. Special Issue. Based on work in collaboration
with C. Wetterich (Heidelberg). 6 page
X-ray and optical properties of Broad Absorption Line Quasars in the Canada-France-Hawaii Telescope Legacy Survey
We study the X-ray and optical properties of 16 Broad Absorption Line (BAL)
quasars detected in about 3 degree square region common to the wide synoptic
(W-1) component of the Canada-France-HawaiiTelescope Legacy Survey (CFHTLS) and
the XMM Large Scale Structure survey (XMM-LSS). The BAL fraction is found to be
10% in full sample, 7% for the optical colour selected QSOs and as high as 33%
if we consider QSOs selected from their IR colours. The X-ray detected non-BAL
and BAL quasars have a mean observed X-ray-to-optical spectral slope of -1.47
+/- 0.13 and -1.66 +/- 0.17 respectively. We also find that the BAL QSOs have
alpha_ox systematically smaller than what is expected from the relationship
between optical luminosity and alpha_ox as derived from our sample. Based on
this, we show, as already reported in the literature for quasars with high
optical luminosities, our new sample of BAL QSOs have X-ray luminosity a factor
of three smaller than what has been found for non-BAL QSOs with similar optical
luminosities. Comparison of hardness ratio of the BAL and non-BAL QSOs suggests
a possible soft X-ray weakness of BAL QSOs. Combining our sample, of relatively
fainter QSOs, with others from the literature we show that larger balnicity
index (BI) and maximum velocity (V_max) of the C IV absorption are correlated
with steeper X-ray to optical spectral index. We argue that this is most likely
a consequence of the existence of a lower envelope in the distribution of BI
(or V_max) values versus optical luminosity. Our results thus show that the
previously known X-ray weakness of BAL QSOs extends to lower optical
luminosities as well.Comment: 12 pages, 12 figures, 3 tables, accepted for publication in MNRA
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