647 research outputs found
Geometric phases and quantum phase transitions
Quantum phase transition is one of the main interests in the field of
condensed matter physics, while geometric phase is a fundamental concept and
has attracted considerable interest in the field of quantum mechanics. However,
no relevant relation was recognized before recent work. In this paper, we
present a review of the connection recently established between these two
interesting fields: investigations in the geometric phase of the many-body
systems have revealed so-called "criticality of geometric phase", in which
geometric phase associated with the many-body ground state exhibits
universality, or scaling behavior in the vicinity of the critical point. In
addition, we address the recent advances on the connection of some other
geometric quantities and quantum phase transitions. The closed relation
recently recognized between quantum phase transitions and some of geometric
quantities may open attractive avenues and fruitful dialog between different
scientific communities.Comment: Invited review article for IJMPB; material covered till June 2007; 10
page
Subtraction at NNLO
We propose a framework for the implementation of a subtraction formalism at
NNLO in QCD, based on an observable- and process-independent cancellation of
infrared singularities. As a first simple application, we present the
calculation of the contribution to the e+e- dijet cross section proportional to
C_F T_RComment: 42 pages Latex; 7 figures included. Modifications to the text, and
references added; the results are unchange
Decay of Loschmidt Echo Enhanced by Quantum Criticality
We study the transition of a quantum system from a pure state to a mixed
one, which is induced by the quantum criticality of the surrounding system
coupled to it. To characterize this transition quantitatively, we carefully
examine the behavior of the Loschmidt echo (LE) of modelled as an Ising
model in a transverse field, which behaves as a measuring apparatus in quantum
measurement. It is found that the quantum critical behavior of strongly
affects its capability of enhancing the decay of LE: near the critical value of
the transverse field entailing the happening of quantum phase transition, the
off-diagonal elements of the reduced density matrix describing vanish
sharply.Comment: 4 pages, 3 figure
Derivation of the cubic NLS and Gross-Pitaevskii hierarchy from manybody dynamics in based on spacetime norms
We derive the defocusing cubic Gross-Pitaevskii (GP) hierarchy in dimension
, from an -body Schr\"{o}dinger equation describing a gas of
interacting bosons in the GP scaling, in the limit . The
main result of this paper is the proof of convergence of the corresponding
BBGKY hierarchy to a GP hierarchy in the spaces introduced in our previous work
on the well-posedness of the Cauchy problem for GP hierarchies,
\cite{chpa2,chpa3,chpa4}, which are inspired by the solutions spaces based on
space-time norms introduced by Klainerman and Machedon in \cite{klma}. We note
that in , this has been a well-known open problem in the field. While our
results do not assume factorization of the solutions, consideration of
factorized solutions yields a new derivation of the cubic, defocusing nonlinear
Schr\"odinger equation (NLS) in .Comment: 44 pages, AMS Late
Political scandal at the end of ideology? The mediatized politics of the Bo Xilai case
In this article, I use the high-profile Bo Xilai case to illustrate the dialectics of media and politics in contemporary China. I start by explaining some of the similarities and key differences between mediatized politics in the West and in China. This leads to an emphasis on the ideological dimension of media logic that is largely missing from discussions derived from a liberal democratic context. I then analyze the dialectics of the mediatized ideological struggle and politicized media logic running through the Bo Xilai scandal. In the last section, I summarize the theoretical contributions that the Chinese case makes to the study of mediatized politics
Low-value care practice in headache: a Spanish mixed methods research study
Background Headache is one of the most prevalent diseases. The Global Burden of Disease Study ranks it as the seventh most common disease overall and the second largest neurological cause of disability in the world. The "Do Not Do" recommendations are a strategy for increasing the quality of care and reducing the cost of care for headache. This study aimed to identify specific low-value practices in headache care, determine their frequency, and estimate the cost overrun that they represent, in order to establish "Do not Do" recommendations specifically for headache by consensus and according to scientific evidence. Methods This was a mixed methods research study that combined qualitative consensus-building techniques, involving a multidisciplinary panel of experts to define the "Do Not Do" recommendations in headache care, and a retrospective observational study with review of a randomized set of patient records from the past 6 months in four hospitals, to quantify the frequency of these "Do Not Do" practices. We calculated the sum of direct costs of medical consultations, medicines, and unnecessary diagnostic tests. Results Seven "Do Not Do" recommendations were established for headache. In total, 3507 medical records were randomly reviewed. Low-value practices had a highly variable occurrence, depending on the hospital and type of headache. Overall, 34.1% of low-value practices were related to treatment, 21% were related to overuse of imaging in consultation, and 19% were related to emergency care. The estimated cost of low-value practices in the four hospitals was 203,520.47 euros per 1000 patients. Conclusions This study identified low-value headache practices that need to be eradicated and provided data on their frequency and cost overruns
Decoherence, the measurement problem, and interpretations of quantum mechanics
Environment-induced decoherence and superselection have been a subject of
intensive research over the past two decades, yet their implications for the
foundational problems of quantum mechanics, most notably the quantum
measurement problem, have remained a matter of great controversy. This paper is
intended to clarify key features of the decoherence program, including its more
recent results, and to investigate their application and consequences in the
context of the main interpretive approaches of quantum mechanics.Comment: 41 pages. Final published versio
‘Team GB’ or ‘Team Scotland’? Media representations of ‘Britishness’ and ‘Scottishness’ at London 2012 and Glasgow 2014
This article critically reflects upon media coverage of the 2012 London Olympic Games and the 2014 Glasgow Commonwealth Games, scrutinising the emergent discursive constructions of ‘Britishness’ and ‘Scottishness’ through an examination of both London-based (English) and Scotland-based publications. Drawing upon Dayan and Katz’s (1992) portrayal of ‘media events’, the article explores how both events presented competing sites of symbolic struggle during a period of constitutional and political turmoil. Consideration is given to the existence of a ‘hegemonic Britishness’ in print media narratives of these events, as evident in the emergent connotations associated with ‘British nationalism’ and ‘Scottish separatism’
Search for the glueball candidates f0(1500) and fJ(1710) in gamma gamma collisions
Data taken with the ALEPH detector at LEP1 have been used to search for gamma
gamma production of the glueball candidates f0(1500) and fJ(1710) via their
decay to pi+pi-. No signal is observed and upper limits to the product of gamma
gamma width and pi+pi- branching ratio of the f0(1500) and the fJ(1710) have
been measured to be Gamma_(gamma gamma -> f0(1500)). BR(f0(1500)->pi+pi-) <
0.31 keV and Gamma_(gamma gamma -> fJ(1710)). BR(fJ(1710)->pi+pi-) < 0.55 keV
at 95% confidence level.Comment: 10 pages, 3 figure
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