32 research outputs found
An Extension of the Faddeev-Jackiw Technique to Fields in Curved Spacetimes
The Legendre transformation on singular Lagrangians, e.g. Lagrangians
representing gauge theories, fails due to the presence of constraints. The
Faddeev-Jackiw technique, which offers an alternative to that of Dirac, is a
symplectic approach to calculating a Hamiltonian paired with a well-defined
initial value problem when working with a singular Lagrangian. This phase space
coordinate reduction was generalized by Barcelos-Neto and Wotzasek to simplify
its application. We present an extension of the Faddeev-Jackiw technique for
constraint reduction in gauge field theories and non-gauge field theories that
are coupled to a curved spacetime that is described by General Relativity. A
major difference from previous formulations is that we do not explicitly
construct the symplectic matrix, as that is not necessary. We find that the
technique is a useful tool that avoids some of the subtle complications of the
Dirac approach to constraints. We apply this formulation to the Ginzburg-Landau
action and provide a calculation of its Hamiltonian and Poisson brackets in a
curved spacetime.Comment: 30 pages, updated to reflect published versio
Do Dark Matter Axions Form a Condensate with Long-Range Correlation?
Recently there has been significant interest in the claim that dark matter
axions gravitationally thermalize and form a Bose-Einstein condensate with
cosmologically long-range correlation. This has potential consequences for
galactic scale observations. Here we critically examine this claim. We point
out that there is an essential difference between the thermalization and
formation of a condensate due to repulsive interactions, which can indeed drive
long-range order, and that due to attractive interactions, which can lead to
localized Bose clumps (stars or solitons) that only exhibit short range
correlation. While the difference between repulsion and attraction is not
present in the standard collisional Boltzmann equation, we argue that it is
essential to the field theory dynamics, and we explain why the latter analysis
is appropriate for a condensate. Since the axion is primarily governed by
attractive interactions -- gravitation and scalar-scalar contact interactions
-- we conclude that while a Bose-Einstein condensate is formed, the claim of
long-range correlation is unjustified.Comment: New version matches the version to be published in Physical Review D
and includes a clarification about the non-relativistic limi
Scalar dark matter vortex stabilization with black holes
Galaxies and their dark-matter halos are commonly presupposed to spin. But it
is an open question how this spin manifests in halos and soliton cores made of
scalar dark matter (SDM, including fuzzy/wave/ultralight-axion dark matter).
One way spin could manifest in a necessarily irrotational SDM velocity field is
with a vortex. But recent results have cast doubt on this scenario, finding
that vortices are generally unstable except with substantial repulsive
self-interaction. In this paper, we introduce an alternative route to
stability: in both (non-relativistic) analytic calculations and simulations, a
black hole or other central mass at least as massive as a soliton can stabilize
a vortex within it. This conclusion may also apply to AU-scale halos bound to
the sun and stellar-mass-scale Bose stars.Comment: Accepted by JCAP. 22 pages, 5 figures. Supplementary animations at
https://doi.org/10.5281/zenodo.7675830 or
https://www.youtube.com/playlist?list=PLHrf0iQS5SY7Xt2sjqskF3kmHd00Hrdf
Neutrinos, Cosmic Rays and the MeV Band
The possible association of the blazar TXS 0506+056 with a high-energy
neutrino detected by IceCube holds the tantalizing potential to answer three
astrophysical questions: 1. Where do high-energy neutrinos originate? 2. Where
are cosmic rays produced and accelerated? 3. What radiation mechanisms produce
the high-energy {\gamma}-rays in blazars? The MeV gamma-ray band holds the key
to these questions, because it is an excellent proxy for photo-hadronic
processes in blazar jets, which also produce neutrino counterparts. Variability
in MeV gamma-rays sheds light on the physical conditions and mechanisms that
take place in the particle acceleration sites in blazar jets. In addition,
hadronic blazar models also predict a high level of polarization fraction in
the MeV band, which can unambiguously distinguish the radiation mechanism.
Future MeV missions with a large field of view, high sensitivity, and
polarization capabilities will play a central role in multi-messenger
astronomy, since pointed, high-resolution telescopes will follow neutrino
alerts only when triggered by an all-sky instrument.Comment: White paper submitted to the Astro2020 Decadal Surve
Prospects for Pulsar Studies at MeV Energies
Enabled by the Fermi Large Area Telescope, we now know that pulsars fill the gamma-ray sky, and we are beginning to understand their emission mechanism and their distribution throughout the Galaxy. To address key questions calls for a sensitive, wide-field MeV telescope, which can detect the population of MeV-peaked pulsars hinted at by Fermi
Prompt Emission Polarimetry of Gamma-Ray Bursts
Many aspects of astrophysical jets can be studied by measuring the polarization of the prompt emission from GRBs. Theoretical models show that a more complete understanding of the inner structure of GRBs, including the geometry and physical processes close to the central engine, can only be achieved by gamma-ray polarimetry
Relative-locality distant observers and the phenomenology of momentum-space geometry
We study the translational invariance of the relative-locality framework
proposed in arXiv:1101.0931, which had been previously established only for the
case of a single interaction. We provide an explicit example of boundary
conditions at endpoints of worldlines, which indeed ensures the desired
translational invariance for processes involving several interactions, even
when some of the interactions are causally connected (particle exchange). We
illustrate the properties of the associated relativistic description of distant
observers within the example of a -Poincar\'e-inspired momentum-space
geometry, with de Sitter metric and parallel transport governed by a non-metric
and torsionful connection. We find that in such a theory simultaneously-emitted
massless particles do not reach simultaneously a distant detector, as expected
in light of the findings of arXiv:1103.5626 on the implications of non-metric
connections. We also show that the theory admits a free-particle limit, where
the relative-locality results of arXiv:1102.4637 are reproduced. We establish
that the torsion of the -Poincar\'e connection introduces a small (but
observably-large) dependence of the time of detection, for
simultaneously-emitted particles, on some properties of the interactions
producing the particles at the source.Comment: 45 pages, 10 figure
Astro2020 Must Issue Actionable Recommendations Regarding Diversity, Inclusion, and Harassment
The 2010 Decadal survey failed to issue any recommendations on diversity and inclusion.Astro2020 cannot make the same mistake. Findings can be ignored by funding agencies;recommendations cannot. In the past decade, multiple groups have assembled detailed actionplans to fix a broken climate within our profession. Astro2020 should play a key role, bysynthesizing this work to produce actionable recommendations to support diversity andinclusion and stop harassment within our profession