44,839 research outputs found
Exact and approximate dynamics of the quantum mechanical O(N) model
We study a quantum dynamical system of N, O(N) symmetric, nonlinear
oscillators as a toy model to investigate the systematics of a 1/N expansion.
The closed time path (CTP) formalism melded with an expansion in 1/N is used to
derive time evolution equations valid to order 1/N (next-to-leading order). The
effective potential is also obtained to this order and its properties
areelucidated. In order to compare theoretical predictions against numerical
solutions of the time-dependent Schrodinger equation, we consider two initial
conditions consistent with O(N) symmetry, one of them a quantum roll, the other
a wave packet initially to one side of the potential minimum, whose center has
all coordinates equal. For the case of the quantum roll we map out the domain
of validity of the large-N expansion. We discuss unitarity violation in the 1/N
expansion; a well-known problem faced by moment truncation techniques. The 1/N
results, both static and dynamic, are also compared to those given by the
Hartree variational ansatz at given values of N. We conclude that late-time
behavior, where nonlinear effects are significant, is not well-described by
either approximation.Comment: 16 pages, 12 figrures, revte
Vacuum Structure of Two-Dimensional Theory on the Orbifold
We consider the vacuum structure of two-dimensional theory on
both in the bosonic and the supersymmetric cases. When the size
of the orbifold is varied, a phase transition occurs at , where
is the mass of . For , there is a unique vacuum, while for
, there are two degenerate vacua. We also obtain the 1-loop quantum
corrections around these vacuum solutions, exactly in the case of and
perturbatively for greater than but close to . Including the
fermions we find that the "chiral" zero modes around the fixed points are
different for . As for the quantum corrections, the
fermionic contributions cancel the singular part of the bosonic contributions
at L=0. Then the total quantum correction has a minimum at the critical length
.Comment: Revtex, 15 pages, 3 eps figure
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Trade Promotion Authority (TPA): Frequently Asked Questions
Trade Promotion Authority (TPA), formerly called fast track, is the authority Congress has granted to the President for limited periods of time to negotiate reciprocal trade agreements. The authority lays out U.S. trade negotiating objectives, procedures for congressional-executive notification and consultation, and expedited legislative procedures under which bills implementing trade agreements negotiated by the executive branch are to be considered. The most recent authority was enacted in December 2002 and expired as of July 1, 2007. Legislation to reauthorize TPA has been introduced in the 113th Congress. The United States is engaged in several sets of trade agreement negotiations. The issue of TPA reauthorization has raised a number of questions regarding TPA itself and the pending legislation. This report addresses a number of those questions that are frequently asked, including:
âą What is trade promotion authority?
âą Is TPA necessary?
âą What are trade negotiating objectives and how are they reflected in TPA statutes?
âą What requirements does Congress impose on the President under TPA?
âą Does TPA affect congressional authority on trade policy
Renormalized broken-symmetry Schwinger-Dyson equations and the 2PI-1/N expansion for the O(N) model
We derive the renormalized Schwinger-Dyson equations for the one- and
two-point functions in the auxiliary field formulation of
field theory to order 1/N in the 2PI-1/N expansion. We show that the
renormalization of the broken-symmetry theory depends only on the counter terms
of the symmetric theory with . We find that the 2PI-1/N expansion
violates the Goldstone theorem at order 1/N. In using the O(4) model as a low
energy effective field theory of pions to study the time evolution of
disoriented chiral condensates one has to {\em{explicitly}} break the O(4)
symmetry to give the physical pions a nonzero mass. In this effective theory
the {\em additional} small contribution to the pion mass due to the violation
of the Goldstone theorem in the 2-PI-1/N equations should be numerically
unimportant
Non-equilibrium dynamics in quantum field theory at high density: the tsunami
The dynamics of a dense relativistic quantum fluid out of thermodynamic
equilibrium is studied in the framework of the Phi^4 scalar field theory in the
large N limit. The time evolution of a particle distribution in momentum space
(the tsunami) is computed. The effective mass felt by the particles in such a
high density medium equals the tree level mass plus the expectation value of
the squared field. The case of negative tree level squared mass is particularly
interesting. In such case dynamical symmetry restoration as well as dynamical
symmetry breaking can happen. Furthermore, the symmetry may stay broken with
vanishing asymptotic squared mass showing the presence of out of equilibrium
Goldstone bosons. We study these phenomena and identify the set of initial
conditions that lead to each case. We compute the equation of state which turns
to depend on the initial state. Although the system does not thermalize, the
equation of state for asymptotically broken symmetry is of radiation type. We
compute the correlation functions at equal times. The two point correlator for
late times is the sum of different terms. One stems from the initial particle
distribution. Another term accounts for the out of equilibrium Goldstone bosons
created by spinodal unstabilities when the symmetry is asymptotically
broken.Both terms are of the order of the inverse of the coupling for distances
where causal signals can connect the two points. The contribution of the out of
equilibrium Goldstones exhibits scaling behaviour in a generalized sense.Comment: LaTex, 49 pages, 15 .ps figure
Machine learning with the hierarchyâofâhypotheses (HoH) approach discovers novel pattern in studies on biological invasions
Research synthesis on simple yet general hypotheses and ideas is challenging in scientific disciplines studying highly contextâdependent systems such as medical, social, and biological sciences. This study shows that machine learning, equationâfree statistical modeling of artificial intelligence, is a promising synthesis tool for discovering novel patterns and the source of controversy in a general hypothesis. We apply a decision tree algorithm, assuming that evidence from various contexts can be adequately integrated in a hierarchically nested structure. As a case study, we analyzed 163 articles that studied a prominent hypothesis in invasion biology, the enemy release hypothesis. We explored if any of the nine attributes that classify each study can differentiate conclusions as classification problem. Results corroborated that machine learning can be useful for research synthesis, as the algorithm could detect patterns that had been already focused in previous narrative reviews. Compared with the previous synthesis study that assessed the same evidence collection based on experts' judgement, the algorithm has newly proposed that the studies focusing on Asian regions mostly supported the hypothesis, suggesting that more detailed investigations in these regions can enhance our understanding of the hypothesis. We suggest that machine learning algorithms can be a promising synthesis tool especially where studies (a) reformulate a general hypothesis from different perspectives, (b) use different methods or variables, or (c) report insufficient information for conducting metaâanalyses
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The Trans-Pacific Partnership: Negotiations and Issues for Congress
[Excerpt] The Trans-Pacific Partnership (TPP) is a potential free trade agreement (FTA) among 11, and perhaps more, countries. The United States and 10 other countries of the Asia-Pacific regionâ Australia, Brunei, Canada, Chile, Malaysia, Mexico, New Zealand, Peru, Singapore, and Vietnamâare negotiating the text of the FTA. Canada and Mexico participated for the first time in the Auckland round of negotiations in December 2012, and Japan recently announced it would seek to participate in the negotiations. With 29 chapters under negotiation, the TPP partners envision the agreement to be âcomprehensive and high-standard,â in that they seek to eliminate tariffs and non-tariff barriers to trade in goods, services, and agriculture, and to establish rules on a wide range of issues including foreign direct investment and other economic activities. They also strive to create a â21st-century agreementâ that addresses new and cross-cutting issues presented by an increasingly globalized economy.
The TPP draws congressional interest on a number of fronts. Congress would have to approve implementing legislation for U.S. commitments under the agreement to enter into force. In addition, under long-established executive-legislative practice, the Administration notifies and consults with congressional leaders, before, during, and after trade agreements have been negotiated. Furthermore, the TPP will likely affect a range of sectors and regions of the U.S. economy of direct interest to Members of Congress and could influence the shape and path of U.S. trade policy for the foreseeable future.
This report examines the issues related to the proposed TPP, the state and substance of the negotiations (to the degree that the information is publically available), the specific areas under negotiation, the policy and economic contexts in which the TPP would fit, and the issues for Congress that the TPP presents. The report will be revised and updated as events warrant
-graded Heisenberg algebras and deformed supersymmetries
The notion of -grading on the enveloping algebra generated by products of
q-deformed Heisenberg algebras is introduced for complex number in the unit
disc. Within this formulation, we consider the extension of the notion of
supersymmetry in the enveloping algebra. We recover the ordinary
grading or Grassmann parity for associative superalgebra, and a modified
version of the usual supersymmetry. As a specific problem, we focus on the
interesting limit for which the Arik and Coon deformation of the
Heisenberg algebra allows to map fermionic modes to bosonic ones in a modified
sense. Different algebraic consequences are discussed.Comment: 2 figure
The von Neumann-Wigner type potentials and the wave functions' asymptotics for the discrete levels in continuum
One to one correspondence between the decay law of the von Neumann-Wigner
type potentials and the asymptotic behaviour of the wave functions representing
bound states in the continuum is established.Comment: latex, 7 page
Perceptually smooth timbral guides by state-space analysis of phase-vocoder parameters
Sculptor is a phase-vocoder-based package of programs
that allows users to explore timbral manipulation
of sound in real time. It is the product
of a research program seeking ultimately to perform
gestural capture by analysis of the sound a
performer makes using a conventional instrument.
Since the phase-vocoder output is of high dimensionality â
typically more than 1,000 channels per
analysis frameâmapping phase-vocoder output to
appropriate input parameters for a synthesizer is
only feasible in theory
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