10,139 research outputs found
Short-distance and short-time structure of a unitary Fermi gas
We consider the operator product expansions for unitarity fermions. We
compute the dynamic structure factor S(q,w) at large frequency and wavenumber
away from the one-particle peak. The overall normalization of S(q,w) is
determined by Tan's contact parameter, and the dependence on q and w is
obtained in closed analytic form. We also find energy deposited into the system
by small, rapid variations of the inverse scattering length.Comment: 11 pages, 8 figure
Universal four-component Fermi gas in one dimension
A four-component Fermi gas in one dimension with a short-range four-body
interaction is shown to exhibit a one-dimensional analog of the BCS-BEC
crossover. Its low-energy physics is governed by a Tomonaga-Luttinger liquid
with three spin gaps. The spin gaps are exponentially small in the weak
coupling (BCS) limit where they arise from the charge-density-wave instability,
and become large in the strong coupling (BEC) limit because of the formation of
tightly-bound tetramers. We investigate the ground-state energy, the sound
velocity, and the gap spectrum in the BCS-BEC crossover and discuss exact
relationships valid in our system. We also show that a one-dimensional analog
of the Efimov effect occurs for five bosons while it is absent for fermions.
Our work opens up a very rich new field of universal few-body and many-body
physics in one dimension.Comment: 9 pages, 3 figures; (v2) Efimov effect for 5 bosons in 1D is
discussed; (v3) expanded versio
Conformality Lost
We consider zero-temperature transitions from conformal to non-conformal
phases in quantum theories. We argue that there are three generic mechanisms
for the loss of conformality in any number of dimensions: (i) fixed point goes
to zero coupling, (ii) fixed point runs off to infinite coupling, or (iii) an
IR fixed point annihilates with a UV fixed point and they both disappear into
the complex plane. We give both relativistic and non-relativistic examples of
the last case in various dimensions and show that the critical behavior of the
mass gap behaves similarly to the correlation length in the finite temperature
Berezinskii-Kosterlitz-Thouless (BKT) phase transition in two dimensions, xi ~
exp(c/|T-T_c|^{1/2}). We speculate that the chiral phase transition in QCD at
large number of fermion flavors belongs to this universality class, and attempt
to identify the UV fixed point that annihilates with the Banks-Zaks fixed point
at the lower end of the conformal window.Comment: 30 pages, 6 figures; v2: typos fixed, references adde
Lorentz Invariance in Chiral Kinetic Theory
We show that Lorentz invariance is realized nontrivially in the classical
action of a massless spin- particle with definite helicity. We find
that the ordinary Lorentz transformation is modified by a shift orthogonal to
the boost vector and the particle momentum. The shift ensures angular momentum
conservation in particle collisions and implies a nonlocality of the collision
term in the Lorentz-invariant kinetic theory due to side jumps. We show that
2/3 of the chiral-vortical effect for a uniformly rotating particle
distribution can be attributed to the magnetic moment coupling required by the
Lorentz invariance. We also show how the classical action can be obtained by
taking the classical limit of the path integral for a Weyl particle.Comment: 5 pages, 1 figur
Searching for magnetic monopoles trapped in accelerator material at the Large Hadron Collider
If produced in high energy particle collisions at the LHC, magnetic monopoles
could stop in material surrounding the interaction points. Obsolete parts of
the beam pipe near the CMS interaction region, which were exposed to the
products of pp and heavy ion collisions, were analysed using a SQUID-based
magnetometer. The purpose of this work is to quantify the performance of the
magnetometer in the context of a monopole search using a small set of samples
of accelerator material ahead of the 2013 shutdown.Comment: 11 page
Probing spacetime foam with extragalactic sources
Due to quantum fluctuations, spacetime is probably ``foamy'' on very small
scales. We propose to detect this texture of spacetime foam by looking for
core-halo structures in the images of distant quasars. We find that the Very
Large Telescope interferometer will be on the verge of being able to probe the
fabric of spacetime when it reaches its design performance. Our method also
allows us to use spacetime foam physics and physics of computation to infer the
existence of dark energy/matter, independent of the evidence from recent
cosmological observations.Comment: LaTeX, 11 pages, 1 figure; version submitted to PRL; several
references added; very useful comments and suggestions by Eric Perlman
incorporate
ADL: a graphical design language for real time parallel applications
Designing parallel applications is generally experienced as a tedious and difficult task, especially when hard real-time performance requirements have to be met. This paper
discusses on-going work concerning the construction of a Design Entry System which
supports the design phase of parallel real-time industrial application development. In
particular, in this paper we pay attention to the development and implementation of a
graphical Application Design Language. The work is part of the ESPRIT project Hamlet which
focuses on industrial application of transputer-based systems for commercially strategic
real-time applications
The Hamlet design entry system: an overview of ADL and its environment
Exploiting parallelism for industrial real-time applications has not received much attention compared to scientific applications. The available real-time design methods do not adequately address the issue of parallelism, resulting still in a strong need for low-level tools such as debuggers and monitors. This need illustrates that developing parallel real-time applications is indeed a difficult and tedious task. In this paper we show how problems can be alleviated if an approach is followed that allows for experimentation with designs and implementations. In particular, we discuss a development system that integrates design, implementation, execution, and analysis of real-time applications, putting emphasis on exploitation of parallelism. In the paper we primarily concentrate on the support for application *design*, as we feel that parallelism should essentially be addressed at this level
Gender, poverty and social justice
Views on poverty are deeply rooted in cultural frameworks about the human condition shaped by histories. In the debate on modernity, perspec
- …