1,690 research outputs found
Large N lattice QCD and its extended strong-weak connection to the hypersphere
We calculate an effective Polyakov line action of QCD at large Nc and large
Nf from a combined lattice strong coupling and hopping expansion working to
second order in both, where the order is defined by the number of windings in
the Polyakov line. We compare with the action, truncated at the same order, of
continuum QCD on S^1 x S^d at weak coupling from one loop perturbation theory,
and find that a large Nc correspondence of equations of motion found in
\cite{Hollowood:2012nr} at leading order, can be extended to the next order.
Throughout the paper, we review the background necessary for computing higher
order corrections to the lattice effective action, in order to make higher
order comparisons more straightforward.Comment: 33 pages, 7 figure
Calculating the chiral condensate diagrammatically at strong coupling
We calculate the chiral condensate of QCD at infinite coupling as a function
of the number of fundamental fermion flavours using a lattice diagrammatic
approach inspired by recent work of Tomboulis, and other work from the 80's. We
outline the approach where the diagrams are formed by combining a truncated
number of sub-diagram types in all possible ways. Our results show evidence of
convergence and agreement with simulation results at small Nf. However,
contrary to recent simulation results, we do not observe a transition at a
critical value of Nf. We further present preliminary results for the chiral
condensate of QCD with symmetric or adjoint representation fermions at infinite
coupling as a function of Nf for Nc = 3. In general, there are sources of error
in this approach associated with miscounting of overlapping diagrams, and
over-counting of diagrams due to symmetries. These are further elaborated upon
in a longer paper.Comment: presented at the 32nd International Symposium on Lattice Field Theory
(Lattice 2014), 23-28 June 2014, New York, NY, US
Identifying Better Effective Higgsless Theories via W_L W_L Scattering
The three site Higgsless model has been offered as a benchmark for studying
the collider phenomenology of Higgsless models. In this talk, we present how
well the three site Higgsless model performs as a general representative of
Higgsless models in describing W_L W_L scattering, and which modifications can
make it more representative. We employ general sum rules relating the masses
and couplings of the Kaluza-Klein (KK) modes of the gauge fields in continuum
and deconstructed Higgsless models as a way to compare the different theories.
After comparing the three site Higgsless model to flat and warped continuum
Higgsless models, we analyze an extensions of the three site Higgsless model,
namely, the Hidden Local Symmetry (HLS) Higgsless model. We demonstrate that
W_LW_L scattering in the HLS Higgsless model can very closely approximate
scattering in the continuum models, provided that the parameter `a' is chosen
to mimic rho-meson dominance of pi-pi scattering in QCD
Calculating the chiral condensate of QCD at infinite coupling using a generalised lattice diagrammatic approach
We develop a lattice diagrammatic technique for calculating the chiral
condensate of QCD at infinite coupling inspired by recent work of Tomboulis and
earlier work from the 80's. The technique involves calculating the contribution
of gauge link diagrams formed from all possible combinations of a number of
sub-diagram types. This is achieved by performing a resummation, using a
truncated number of sub-diagram types. We show how to calculate the relevant
sub-diagrams, including a new technique for evaluating group integrals with
arbitrary number of gauge link elements, using Young Projectors. Including up
to four different diagram types we calculate the chiral condensate as a
function of Nf, and show that two real solutions result, which are non-zero for
all integer Nf. We analyse these solutions and find signs of convergence of the
expansion at small Nf. We discuss sources of error associated with this
approach in detail and implement a technique to reduce over-counting of
diagrams.Comment: 47 pages, including 2 appendices, 10 plot
The Octave (Birmingham - Sheffield Hallam) automated pipeline for extracting oscillation parameters of solar-like main-sequence stars
The number of main-sequence stars for which we can observe solar-like
oscillations is expected to increase considerably with the short-cadence
high-precision photometric observations from the NASA Kepler satellite. Because
of this increase in number of stars, automated tools are needed to analyse
these data in a reasonable amount of time. In the framework of the asteroFLAG
consortium, we present an automated pipeline which extracts frequencies and
other parameters of solar-like oscillations in main-sequence and subgiant
stars. The pipeline uses only the timeseries data as input and does not require
any other input information. Tests on 353 artificial stars reveal that we can
obtain accurate frequencies and oscillation parameters for about three quarters
of the stars. We conclude that our methods are well suited for the analysis of
main-sequence stars, which show mainly p-mode oscillations.Comment: accepted by MNRA
Future Perspectives on GLP-1 Receptor Agonists and GLP-1/glucagon Receptor Co-agonists in the Treatment of NAFLD
Along the obesity pandemic, the prevalence of non-alcoholic fatty liver disease (NAFLD), often regarded as the hepatic manifestation of the metabolic syndrome, increases worldwide representing now the prevalent liver disease in western countries. No pharmacotherapy is approved for the treatment of NAFLD and, currently, the cornerstone treatment is lifestyle modifications focusing on bodyweight loss, notoriously difficult to obtain and even more difficult to maintain. Thus, novel therapeutic approaches are highly demanded. Glucagon-like peptide-1 (GLP-1) receptor agonists (GLP-1RAs) are approved for the treatment of type 2 diabetes and obesity. They exert their body weight-lowering effect by reducing satiety and food intake. GLP-1RAs have also been shown to reduce liver inflammation and fibrosis. Furthermore, glucagon receptor agonism is being investigated for the treatment of NAFLD due to its appetite and food intake-reducing effects, as well as its ability to increase lipid oxidation and thermogenesis. Recent studies suggest that glucagon receptor signaling is disrupted in NAFLD, indicating that supra-physiological glucagon receptor agonism might represent a new NAFLD treatment target. The present review provides (1) an overview in the pathophysiology of NAFLD, including the potential involvement of GLP-1 and glucagon, (2) an introduction to the currently available GLP-1RAs and (3) outlines the potential of emerging GLP-1RAs and GLP-1/glucagon receptor co-agonists in the treatment of NAFLD
ASTEC -- the Aarhus STellar Evolution Code
The Aarhus code is the result of a long development, starting in 1974, and
still ongoing. A novel feature is the integration of the computation of
adiabatic oscillations for specified models as part of the code. It offers
substantial flexibility in terms of microphysics and has been carefully tested
for the computation of solar models. However, considerable development is still
required in the treatment of nuclear reactions, diffusion and convective
mixing.Comment: Astrophys. Space Sci, in the pres
Low abundances of heavy elements in the solar outer layers: comparisons of solar models with helioseismic inversions
Recent solar photospheric abundance analyses have led to a significant
reduction of the metal abundances compared to the previous determinations. The
solar models computed with standard opacities and diffusion processes using
these new abundances give poor agreement with helioseismic inversions for the
sound-speed profile, the surface helium abundance, and the convective zone
depth.
We attempt to obtain a good agreement between helioseismic inversions and
solar models which present the "old" mixture in the interior and new chemical
composition in the convective zone. To reach this result, we assume an
undermetallic accretion at the beginning of the main sequence.
We compute solar models with the Toulouse-Geneva Evolution Code, in which we
simulate an undermetallic accretion in the early stages of the main sequence,
in order to obtain new mixture in the outer convective zone. We compare the
sound-speed profile, the convective zone depth, and the surface helium
abundance with those deduced from helioseismology.
The model with accretion but without any mixing process inside is in better
agreement with helioseismology than the solar model with the new abundances
throughout. There is, however, a spike under the convective zone which reaches
3.4%. Furthermore, the convective zone depth and the surface helium abundance
are too low. Introducing undershooting below the convective zone allows us to
recover the good convective zone radius and the addition of rotation-induced
mixing and tachocline allows us to reconcile the surface helium abundance. But
in any case the agreement of the sound-speed profile with helioseismic
inference is worse than obtained with the old abundances.Comment: 5 pages, 2 figure
Abrupt permafrost thaw triggers activity of copiotrophs and microbiome predators
Permafrost soils store a substantial part of the global soil carbon and nitrogen. However, global warming causes abrupt erosion and
gradual thaw, which make these stocks vulnerable to microbial decomposition into greenhouse gases. Here, we investigated the microbial response to abrupt in situ permafrost thaw. We sequenced the total RNA of a 1 m deep soil core consisting of up to 26 500-year-old
permafrost material from an active abrupt erosion site. We analysed the microbial community in the active layer soil, the recently
thawed, and the intact permafrost, and found maximum RNA:DNA ratios in recently thawed permafrost indicating a high microbial
activity. In thawed permafrost, potentially copiotrophic Burkholderiales and Sphingobacteriales, but also microbiome predators dominated the community. Overall, both thaw-dependent and long-term soil properties significantly correlated with changes in community composition, as did microbiome predator abundance. Bacterial predators were dominated in shallower depths by Myxococcota,
while protozoa, especially Cercozoa and Ciliophora, almost tripled in relative abundance in thawed layers. Our findings highlight the
ecological importance of a diverse interkingdom and active microbial community highly abundant in abruptly thawing permafrost,
as well as predation as potential biological control mechanism
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