141 research outputs found
Constructing the Tree-Level Yang-Mills S-Matrix Using Complex Factorization
A remarkable connection between BCFW recursion relations and constraints on
the S-matrix was made by Benincasa and Cachazo in 0705.4305, who noted that
mutual consistency of different BCFW constructions of four-particle amplitudes
generates non-trivial (but familiar) constraints on three-particle coupling
constants --- these include gauge invariance, the equivalence principle, and
the lack of non-trivial couplings for spins >2. These constraints can also be
derived with weaker assumptions, by demanding the existence of four-point
amplitudes that factorize properly in all unitarity limits with complex
momenta. From this starting point, we show that the BCFW prescription can be
interpreted as an algorithm for fully constructing a tree-level S-matrix, and
that complex factorization of general BCFW amplitudes follows from the
factorization of four-particle amplitudes. The allowed set of BCFW deformations
is identified, formulated entirely as a statement on the three-particle sector,
and using only complex factorization as a guide. Consequently, our analysis
based on the physical consistency of the S-matrix is entirely independent of
field theory. We analyze the case of pure Yang-Mills, and outline a proof for
gravity. For Yang-Mills, we also show that the well-known scaling behavior of
BCFW-deformed amplitudes at large z is a simple consequence of factorization.
For gravity, factorization in certain channels requires asymptotic behavior
~1/z^2.Comment: 35 pages, 6 figure
From dense-dilute duality to self duality in high energy evolution
I describe recent work on inclusion of Pomeron loops in the high energy
evolution. In particular I show that the complete eikonal high energy evolution
kernel must be selfdual.Comment: Talk given at DIS05, April 2005, Madiso
Red Supergiants in the Andromeda Galaxy (M31)
Red supergiants are a short-lived stage in the evolution of moderately
massive stars (10-25Mo), and as such their location in the H-R diagram provides
an exacting test of stellar evolutionary models. Since massive star evolution
is strongly affected by the amount of mass-loss a star suffers, and since the
mass-loss rates depend upon metallicity, it is highly desirable to study the
physical properties of these stars in galaxies of various metallicities. Here
we identify a sample of red supergiants in M31 (the most metal-rich of the
Local Group galaxies) and derive their physical properties by fitting MARCS
atmosphere models to moderate resolution optical spectroscopy, and from V-K
photometry.Comment: Accepted for publication in the Astrophysical Journa
Satellites will address critical science priorities for quantifying ocean carbon
The ability to routinely quantify global carbon dioxide (CO2) absorption by the oceans has become crucial: it provides a powerful constraint for establishing global and regional carbon (C) budgets, and enables identification of the ecological impacts and risks of this uptake on the marine environment. Advances in understanding, technology, and international coordination have made it possible to measure CO2 absorption by the oceans to a greater degree of accuracy than is possible in terrestrial landscapes. These advances, combined with new satellite‐based Earth observation capabilities, increasing public availability of data, and cloud computing, provide important opportunities for addressing critical knowledge gaps. Furthermore, Earth observation in synergy with in‐situ monitoring can provide the large‐scale ocean monitoring that is necessary to support policies to protect ocean ecosystems at risk, and motivate societal shifts toward meeting C emissions targets; however, sustained effort will be needed
An Electron Fixed Target Experiment to Search for a New Vector Boson A' Decaying to e+e-
We describe an experiment to search for a new vector boson A' with weak
coupling alpha' > 6 x 10^{-8} alpha to electrons (alpha=e^2/4pi) in the mass
range 65 MeV < m_A' < 550 MeV. New vector bosons with such small couplings
arise naturally from a small kinetic mixing of the "dark photon" A' with the
photon -- one of the very few ways in which new forces can couple to the
Standard Model -- and have received considerable attention as an explanation of
various dark matter related anomalies. A' bosons are produced by radiation off
an electron beam, and could appear as narrow resonances with small production
cross-section in the trident e+e- spectrum. We summarize the experimental
approach described in a proposal submitted to Jefferson Laboratory's PAC35,
PR-10-009. This experiment, the A' Experiment (APEX), uses the electron beam of
the Continuous Electron Beam Accelerator Facility at Jefferson Laboratory
(CEBAF) at energies of ~1-4 GeV incident on 0.5-10% radiation length Tungsten
wire mesh targets, and measures the resulting e+e- pairs to search for the A'
using the High Resolution Spectrometer and the septum magnet in Hall A. With a
~1 month run, APEX will achieve very good sensitivity because the statistics of
e+e- pairs will be ~10,000 times larger in the explored mass range than any
previous search for the A' boson. These statistics and the excellent mass
resolution of the spectrometers allow sensitivity to alpha'/alpha one to three
orders of magnitude below current limits, in a region of parameter space of
great theoretical and phenomenological interest. Similar experiments could also
be performed at other facilities, such as the Mainz Microtron.Comment: 19 pages, 12 figures, 2 table
The Cosmology of Composite Inelastic Dark Matter
Composite dark matter is a natural setting for implementing inelastic dark
matter - the O(100 keV) mass splitting arises from spin-spin interactions of
constituent fermions. In models where the constituents are charged under an
axial U(1) gauge symmetry that also couples to the Standard Model quarks, dark
matter scatters inelastically off Standard Model nuclei and can explain the
DAMA/LIBRA annual modulation signal. This article describes the early Universe
cosmology of a minimal implementation of a composite inelastic dark matter
model where the dark matter is a meson composed of a light and a heavy quark.
The synthesis of the constituent quarks into dark mesons and baryons results in
several qualitatively different configurations of the resulting dark matter
hadrons depending on the relative mass scales in the system.Comment: 31 pages, 4 figures; references added, typos correcte
On the Nature of Stars with Planets
We consider the metallicities and kinematics of nearby stars known to have
planetary-mass companions in the general context of the overall properties of
the local Galactic Disk. We have used Stromgren photometry to determine
abundances for both the extrasolar-planet host stars and for a volume-limited
sample of 486 F, G and K stars selected from the Hipparcos catalogue. The
latter data show that the Sun lies near the modal abundance of the disk, with
over 45% of local stars having super-solar metallicities. Twenty of the latter
stars (4.1%) are known to have planetary-mass companions. Using that ratio to
scale data for the complete sample of planetary host stars, we find that the
fraction of stars with extrasolar planets rises sharply with increasing
abundance, confirming previous results. However, the frequency remains at the
3-4% level for stars within 0.15 dex of solar abundance, and falls to ~1% only
for stars with abundances less than half solar. Given the present observational
constraints, both in velocity precision and in the available time baseline,
these numbers represent a lower limit to the frequency of extrasolar planetary
systems. A comparison between the kinematics of the planetary host stars and a
representative sample of disk stars suggests that the former have an average
age which is ~60% of the latter.Comment: 46 pages, 13 figures; accepted for PAS
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