85 research outputs found
Non-commutative Gross-Neveu model at large N
The non-commutative O(N) Gross-Neveu model is solved in the large N limit in
two and three space-time dimensions. The commutative version of the two
dimensional model is a renormalizable quantum field theory, both in a coupling
constant expansion and an expansion in 1/N. The non-commutative version has a
renormalizable coupling constant expansion where ultraviolet divergences can be
removed by adjusting counterterms to each order. On the other hand, in a
previous work, we showed that the non-commutative theory is not renormalizable
in the large N expansion. This is argued to be due to a combined effect of
asymptotic freedom and the ultraviolet/infrared mixing that occurs in a
non-commutative field theory. In the present paper we will elaborate on this
result and extend it to study the large N limit of the three dimensional
Gross-Neveu model. We shall see that the large N limit of the three dimensional
theory is also trivial when the ultraviolet cutoff is removed.Comment: 23 page
Thermal Correlators in Little String Theory
We calculate, using holographic duality, the thermal two-point function in
finite temperature little string theory. The analysis of those correlators
reveals possible instabilities of the thermal ensemble, as in previous
discussions of the thermodynamics of little string theory. We comment on the
dependence of the instability on the spatial volume of the system.Comment: 13 page
Closed Timelike Curves and Holography in Compact Plane Waves
We discuss plane wave backgrounds of string theory and their relation to
Goedel-like universes. This involves a twisted compactification along the
direction of propagation of the wave, which induces closed timelike curves. We
show, however, that no such curves are geodesic. The particle geodesics and the
preferred holographic screens we find are qualitatively different from those in
the Goedel-like universes. Of the two types of preferred screen, only one is
suited to dimensional reduction and/or T-duality, and this provides a
``holographic protection'' of chronology. The other type of screen, relevant to
an observer localized in all directions, is constructed both for the compact
and non-compact plane waves, a result of possible independent interest. We
comment on the consistency of field theory in such spaces, in which there are
closed timelike (and null) curves but no closed timelike (or null) geodesics.Comment: 21 pages, 3 figures, LaTe
Mapping Cosmic Dawn and Reionization: Challenges and Synergies
Cosmic dawn and the Epoch of Reionization (EoR) are among the least explored
observational eras in cosmology: a time at which the first galaxies and
supermassive black holes formed and reionized the cold, neutral Universe of the
post-recombination era. With current instruments, only a handful of the
brightest galaxies and quasars from that time are detectable as individual
objects, due to their extreme distances. Fortunately, a multitude of
multi-wavelength intensity mapping measurements, ranging from the redshifted 21
cm background in the radio to the unresolved X-ray background, contain a
plethora of synergistic information about this elusive era. The coming decade
will likely see direct detections of inhomogenous reionization with CMB and 21
cm observations, and a slew of other probes covering overlapping areas and
complementary physical processes will provide crucial additional information
and cross-validation. To maximize scientific discovery and return on
investment, coordinated survey planning and joint data analysis should be a
high priority, closely coupled to computational models and theoretical
predictions.Comment: 5 pages, 1 figure, submitted to the Astro2020 Decadal Survey Science
White Paper cal
Cosmology with the Highly Redshifted 21cm Line
In addition to being a probe of Cosmic Dawn and Epoch of Reionization
astrophysics, the 21cm line at is also a powerful way to constrain
cosmology. Its power derives from several unique capabilities. First, the 21cm
line is sensitive to energy injections into the intergalactic medium at high
redshifts. It also increases the number of measurable modes compared to
existing cosmological probes by orders of magnitude. Many of these modes are on
smaller scales than are accessible via the CMB, and moreover have the advantage
of being firmly in the linear regime (making them easy to model theoretically).
Finally, the 21cm line provides access to redshifts prior to the formation of
luminous objects. Together, these features of 21cm cosmology at provide
multiple pathways toward precise cosmological constraints. These include the
"marginalizing out" of astrophysical effects, the utilization of redshift space
distortions, the breaking of CMB degeneracies, the identification of signatures
of relative velocities between baryons and dark matter, and the discovery of
unexpected signs of physics beyond the CDM paradigm at high redshifts.Comment: Science white paper submitted to Decadal 2020 surve
Running couplings and triviality of field theories on non-commutative spaces
We examine the issue of renormalizability of asymptotically free field
theories on non-commutative spaces. As an example, we solve the non-commutative
O(N) invariant Gross-Neveu model at large N. On commutative space this is a
renormalizable model with non-trivial interactions. On the noncommutative
space, if we take the translation invariant ground state, we find that the
model is non-renormalizable. Removing the ultraviolet cutoff yields a trivial
non-interacting theory.Comment: Latex, 9p, Minor changes, references and clarifications are adde
A Roadmap for Astrophysics and Cosmology with High-Redshift 21 cm Intensity Mapping
In this white paper, we lay out a US roadmap for high-redshift 21 cm
cosmology (30 < z < 6) in the 2020s. Beginning with the currently-funded HERA
and MWA Phase II projects and advancing through the decade with a coordinated
program of small-scale instrumentation, software, and analysis projects
targeting technology development, this roadmap incorporates our current best
understanding of the systematics confronting 21 cm cosmology into a plan for
overcoming them, enabling next-generation, mid-scale 21 cm arrays to be
proposed late in the decade. Submitted for consideration by the Astro2020
Decadal Survey Program Panel for Radio, Millimeter, and Submillimeter
Observations from the Ground as a Medium-Sized Project.Comment: 10 pages (plus a cover page and references), 6 figures. Submitted as
a APC White Paper for Astro202
Structure and Functions of Pediatric Aerodigestive Programs: A Consensus Statement
Aerodigestive programs provide coordinated interdisciplinary care to pediatric patients with complex congenital or acquired conditions affecting breathing, swallowing, and growth. Although there has been a proliferation of programs, as well as national meetings, interest groups and early research activity, there is, as of yet, no consensus definition of an aerodigestive patient, standardized structure, and functions of an aerodigestive program or a blueprint for research prioritization. The Delphi method was used by a multidisciplinary and multi-institutional panel of aerodigestive providers to obtain consensus on 4 broad content areas related to aerodigestive care: (1) definition of an aerodigestive patient, (2) essential construct and functions of an aerodigestive program, (3) identification of aerodigestive research priorities, and (4) evaluation and recognition of aerodigestive programs and future directions. After 3 iterations of survey, consensus was obtained by either a supermajority of 75% or stability in median ranking on 33 of 36 items. This included a standard definition of an aerodigestive patient, level of participation of specific pediatric disciplines in a program, essential components of the care cycle and functions of the program, feeding and swallowing assessment and therapy, procedural scope and volume, research priorities and outcome measures, certification, coding, and funding. We propose the first consensus definition of the aerodigestive care model with specific recommendations regarding associated personnel, infrastructure, research, and outcome measures. We hope that this may provide an initial framework to further standardize care, develop clinical guidelines, and improve outcomes for aerodigestive patients
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