78,738 research outputs found
Diagrammatic insights into next-to-soft corrections
We confirm recently proposed theorems for the structure of next-to-soft
corrections in gauge and gravity theories using diagrammatic techniques, first
developed for use in QCD phenomenology. Our aim is to provide a useful
alternative insight into the next-to-soft theorems, including tools that may be
useful for further study. We also shed light on a recently observed double copy
relation between next-to-soft corrections in the gauge and gravity cases.Comment: 12 pages, 4 figure
The Cornell Potential from General Geometries in AdS / QCD
We consider the heavy quark-antiquark potential in the AdS / QCD
correspondence, focusing in particular on a recently calculated AdS-like metric
deformed by back-reaction effects. We find that tuning the long-distance
behaviour of the potential leads to a discrepancy at small distances, and
discuss how to better constrain AdS / QCD geometries. A systematic comparison
of various geometries is presented, based on goodness of fit to lattice data in
the quenched approximation. The back-reacted geometry is seen to be
phenomenologically favoured over an alternative geometry with the same number
of parameters, although it does not perform as well as some other geometries.Comment: 12 pages, 4 figures. Revised and expanded version to appear in
Physics Letters
New insights into soft gluons and gravitons
The study of gluon radiation in QCD, in the limit of small ("soft") momentum,
remains an active research area, with a variety of phenomenological and
theoretical applications. Soft gluon emission leads to large logarithms in
perturbation theory which have to be summed up to all orders in the coupling,
and also governs the structure of infrared singularities. Recently, new
techniques and mathematical structures have been discovered, which enhance our
understanding of these all-order properties. This contribution will review a
number of key topics, including the relationship between QCD and gravity.Comment: 6 pages, 3 figures; Proceedings of 36th International Conference on
High Energy Physics, July 4-11, 2012, Melbourne, Australi
Room-temperature ballistic transport in narrow graphene strips
We investigate electron-phonon couplings, scattering rates, and mean free
paths in zigzag-edge graphene strips with widths of the order of 10 nm. Our
calculations for these graphene nanostrips show both the expected similarity
with single-wall carbon nanotubes (SWNTs) and the suppression of the
electron-phonon scattering due to a Dirichlet boundary condition that prohibits
one major backscattering channel present in SWNTs. Low-energy acoustic phonon
scattering is exponentially small at room temperature due to the large phonon
wave vector required for backscattering. We find within our model that the
electron-phonon mean free path is proportional to the width of the nanostrip
and is approximately 70 m for an 11-nm-wide nanostrip.Comment: 5 pages and 5 figure
The excess burden of cancer in men in the UK
In general men are at significantly greater risk than women from nearly all of the common cancers that occur in both sexes (with the exception of breast cancer) (White 2009, Wilkins 2006, DH 2007). This report will consider the current overall burden of cancer among men in the UK, estimated from the latest statistics, and outline the extent of the differences between the sexes. All figures and calculations reported here are based on data extracted from the Cancer Research UK CancerStats web pages extracted in June 2009 (Cancer Research UK, 2009)
The classical double copy for Taub-NUT spacetime
The double copy is a much-studied relationship between gauge theory and
gravity amplitudes. Recently, this was generalised to an infinite family of
classical solutions to Einstein's equations, namely stationary Kerr-Schild
geometries. In this paper, we extend this to the Taub-NUT solution in gravity,
which has a double Kerr-Schild form. The single copy of this solution is a
dyon, whose electric and magnetic charges are related to the mass and NUT
charge in the gravity theory. Finally, we find hints that the classical double
copy extends to curved background geometries.Comment: 13 pages, no figures. Minor edits to match journal versio
Resolving the virial discrepancy in clusters of galaxies with modified Newtonian dynamics
A sample of 197 X-ray emitting clusters of galaxies is considered in the
context of Milgrom's modified Newtonian dynamics (MOND). It is shown that the
gas mass, extrapolated via an assumed model to a fixed radius of 3 Mpc,
is correlated with the gas temperature as predicted by MOND (). The observed temperatures are generally consistent with the inferred
mass of hot gas; no substantial quantity of additional unseen matter is
required in the context of MOND. However, modified dynamics cannot resolve the
strong lensing discrepancy in those clusters where this phenomenon occurs. The
prediction is that additional baryonic matter may be detected in the central
regions of rich clusters.Comment: Submitted to A&A, 4 pages, 3 figures, A&A macro
ROSAT PSPC observations of the outer regions of the Perseus cluster of galaxies
We present an analysis of four off-axis ROSAT PSPC observations of the
Perseus cluster of galaxies (Abell~426). We detect the surface brightness
profile to a radius of 80 arcmin ( Mpc) from the X-ray
peak. The profile is measured in various sectors and in three different energy
bands. Firstly, a colour analysis highlights a slight variation of over
the region, and cool components in the core and in the eastern sector. We apply
the -model to the profiles from different sectors and present a solution
to the, so-called, -problem. The residuals from an azimuthally-averaged
profile highlight extended emission both in the East and in the West, with
estimated luminosities of about 8 and 1 , respectively.
We fit several models to the surface brightness profile, including the one
obtained from the Navarro, Frenk and White (1995) potential. We obtain the best
fit with the gas distribution described by a power law in the inner, cooling
region and a -model for the extended emission. Through the best-fit
results and the constraints from the deprojection of the surface brightness
profiles, we define the radius where the overdensity inside the cluster is 200
times the critical value, , at Mpc. Within Mpc (), the total mass in the Perseus cluster is
and its gas fraction is about 30 per cent.Comment: 21 pages, 23 figures; accepted for publication in MNRAS; also
available at http://www-xray.ast.cam.ac.uk/~settori/paper.htm
- …