21 research outputs found
Double Kerr-Schild spacetimes and the Newman-Penrose map
The Newman-Penrose map, which is closely related to the classical double
copy, associates certain exact solutions of Einstein's equations with self-dual
solutions of the vacuum Maxwell equations. Here we initiate an extension of the
Newman-Penrose map to a broader class of spacetimes. As an example, we apply
principles from the Newman-Penrose map to associate a self-dual gauge field to
the Kerr-Taub-NUT-(A)dS spacetime and we show that the result agrees with
previously studied examples of classical double copies. The corresponding field
strength exhibits a discrete electric-magnetic duality that is distinct from
its (Hodge star) self-dual property.Comment: 14 pages + reference
Hamiltonian Truncation Effective Theory
Hamiltonian truncation is a non-perturbative numerical method for calculating observables of a quantum field theory. The starting point for this method is to truncate the interacting Hamiltonian to a finite-dimensional space of states spanned by the eigenvectors of the free Hamiltonian H0 with eigenvalues below some energy cutoff Emax. In this work, we show how to treat Hamiltonian truncation systematically using effective field theory methodology. We define the finite-dimensional effective Hamiltonian by integrating out the states above Emax. The effective Hamiltonian can be computed by matching a transition amplitude to the full theory, and gives corrections order by order as an expansion in powers of 1/Emax. The effective Hamiltonian is non-local, with the non-locality controlled in an expansion in powers of H0/Emax. The effective Hamiltonian is also non-Hermitian, and we discuss whether this is a necessary feature or an artifact of our definition. We apply our formalism to 2D λφ4 theory, and compute the the leading 1/E 2 max corrections to the effective Hamiltonian. We show that these corrections non trivially satisfy the crucial property of separation of scales. Numerical diagonalization of the effective Hamiltonian gives residual errors of order 1/E 3 max, as expected by our power counting. We also present the power counting for 3D λφ4 theory and perform calculations that demonstrate the separation of scales in this theory
The Final SDSS High-Redshift Quasar Sample of 52 Quasars at z>5.7
We present the discovery of nine quasars at identified in the Sloan
Digital Sky Survey (SDSS) imaging data. This completes our survey of
quasars in the SDSS footprint. Our final sample consists of 52 quasars at
, including 29 quasars with mag selected from
11,240 deg of the SDSS single-epoch imaging survey (the main survey), 10
quasars with selected from 4223 deg of the SDSS
overlap regions (regions with two or more imaging scans), and 13 quasars down
to mag from the 277 deg in Stripe 82. They span a
wide luminosity range of . This well-defined sample
is used to derive the quasar luminosity function (QLF) at . After
combining our SDSS sample with two faint ( mag) quasars from
the literature, we obtain the parameters for a double power-law fit to the QLF.
The bright-end slope of the QLF is well constrained to be
. Due to the small number of low-luminosity quasars, the
faint-end slope and the characteristic magnitude are
less well constrained, with and
mag. The spatial density of luminous quasars,
parametrized as , drops rapidly
from to 6, with . Based on our fitted QLF and assuming
an IGM clumping factor of , we find that the observed quasar population
cannot provide enough photons to ionize the IGM at \%
confidence. Quasars may still provide a significant fraction of the required
photons, although much larger samples of faint quasars are needed for more
stringent constraints on the quasar contribution to reionization.Comment: 20 pages, 12 figures, Accepted for publication in The Astrophysical
Journa
SDSS J094604.90+183541.8: A Gravitationally Lensed Quasar at z=4.8
We report the discovery of a gravitationally lensed quasar identified
serendipitously in the Sloan Digital Sky Survey (SDSS). The object, SDSS
J094604.90+183541.8, was initially targeted for spectroscopy as a luminous red
galaxy, but the SDSS spectrum has the features of both a z=0.388 galaxy and a
z=4.8 quasar. We have obtained additional imaging that resolves the system into
two quasar images separated by 3.06 arcsec and a bright galaxy that is strongly
blended with one of the quasar images. We confirm spectroscopically that the
two quasar images represent a single lensed source at z=4.8 with a total
magnification of 3.2, and we derive a model for the lensing galaxy. This is the
highest redshift lensed quasar currently known. We examine the issues
surrounding the selection of such an unusual object from existing data and
briefly discuss implications for lensed quasar surveys.Comment: AJ accepted, 9 pages, 6 figures, referee suggestions include