53 research outputs found
Dark Nuclei I: Cosmology and Indirect Detection
In a companion paper (to be presented), lattice field theory methods are used
to show that in two-color, two-flavor QCD there are stable nuclear states in
the spectrum. As a commonly studied theory of composite dark matter, this
motivates the consideration of possible nuclear physics in this and other
composite dark sectors. In this work, early Universe cosmology and indirect
detection signatures are explored for both symmetric and asymmetric dark
matter, highlighting the unique features that arise from considerations of dark
nuclei and associated dark nuclear processes. The present day dark matter
abundance may be composed of dark nucleons and/or dark nuclei, where the latter
are generated through it dark nucleosynthesis. For symmetric dark matter,
indirect detection signatures are possible from annihilation, dark
nucleosynthesis, and dark nuclear capture and we present a novel explanation of
the galactic center gamma ray excess based on the latter. For asymmetric dark
matter, dark nucleosynthesis may alter the capture of dark matter in stars,
allowing for captured particles to be processed into nuclei and ejected from
the star through dark nucleosynthesis in the core. Notably, dark
nucleosynthesis realizes a novel mechanism for indirect detection signals of
asymmetric dark matter from regions such as the galactic center, without having
to rely on a symmetric dark matter component.Comment: 31 pages, 9 figure
Aspects of hadron and instatnton physics in lattice quantum field theories
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1997.Includes bibliographical references (p. 103-110).by Andrew Pochinsky.Ph.D
Nucleon structure with pion mass down to 149 MeV
We present isovector nucleon observables: the axial, tensor, and scalar
charges and the Dirac radius. Using the BMW clover-improved Wilson action and
pion masses as low as 149 MeV, we achieve good control over chiral
extrapolation to the physical point. Our analysis is done using three different
source-sink separations in order to identify excited-state effects, and we make
use of the summation method to reduce their size.Comment: 7 pages, 5 figures. Talk presented at the 30th International
Symposium on Lattice Field Theory (Lattice 2012), June 24-29, 2012, Cairns,
Australi
Dark nuclei. II. Nuclear spectroscopy in two-color QCD
We consider two-color QCD with two flavors of quarks as a possible theory of composite dark matter and use lattice field theory methods to investigate nuclear spectroscopy in the spin J = 0 and J = 1 multibaryon sectors. We find compelling evidence that J = 1 systems with baryon number B = 2,3 (and their mixed meson-baryon counterparts) are bound states—the analogues of nuclei in this theory. In addition, we estimate the σ-terms of the J = 0 and J = 1 single baryon states which are important for the coupling of the theory to scalar currents that may mediate interactions with the visible sector.Simons Foundation (Postdoctoral Fellowship)United States. Dept. of Energy (Early Career Research Award DE-SC0010495)Solomon Buchsbaum AT&T Research FundUnited States. Dept. of Energy (Grant DE-FG02-94ER40818
Nucleon form factors with light Wilson quarks
We present nucleon observables - primarily isovector vector form factors -
from calculations using 2+1 flavors of Wilson quarks. One ensemble is used for
a dedicated high-precision study of excited-state effects using five
source-sink separations between 0.7 and 1.6 fm. We also present results from a
larger set of calculations that include an ensemble with pion mass 149 MeV and
box size 5.6 fm, which nearly eliminates the uncertainty associated with
extrapolation to the physical pion mass. The results show agreement with
experiment for the vector form factors, which occurs only when excited-state
contributions are reduced. Finally, we show results from a subset of ensembles
that have pion mass 254 MeV with varying temporal and spatial box sizes, which
we use for a controlled study of finite-volume effects and a test of the
"" rule of thumb.Comment: 7 pages, 3 figures. Talk presented at the 31st International
Symposium on Lattice Field Theory (Lattice 2013), July 29-August 3, 2013,
Mainz, German
Computing the nucleon charge and axial radii directly at in lattice QCD
We describe a procedure for extracting momentum derivatives of nucleon matrix
elements on the lattice directly at . This is based on the Rome method
for computing momentum derivatives of quark propagators. We apply this
procedure to extract the nucleon isovector magnetic moment and charge radius as
well as the isovector induced pseudoscalar form factor at and the axial
radius. For comparison, we also determine these quantities with the traditional
approach of computing the corresponding form factors, i.e. and
for the case of the vector current and and
for the axial current, at multiple values followed by
-expansion fits. We perform our calculations at the physical pion mass using
a 2HEX-smeared Wilson-clover action. To control the effects of excited-state
contamination, the calculations were done at three source-sink separations and
the summation method was used. The derivative method produces results
consistent with those from the traditional approach but with larger statistical
uncertainties especially for the isovector charge and axial radii.Comment: 16 pages, 7 figure
High-precision calculation of the strange nucleon electromagnetic form factors
We report a direct lattice QCD calculation of the strange nucleon
electromagnetic form factors and in the kinematic range . For the first time, both and
are shown to be nonzero with high significance. This work uses
closer-to-physical lattice parameters than previous calculations, and achieves
an unprecedented statistical precision by implementing a recently proposed
variance reduction technique called hierarchical probing. We perform
model-independent fits of the form factor shapes using the -expansion and
determine the strange electric and magnetic radii and magnetic moment. We
compare our results to parity-violating electron-proton scattering data and to
other theoretical studies.Comment: 6 pages, 5 figures. v2: references adde
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