985 research outputs found
Spectral expansion for finite temperature two-point functions and clustering
Recently, the spectral expansion of finite temperature two-point functions in
integrable quantum field theories was constructed using a finite volume
regularization technique and the application of multidimensional residues. In
the present work, the original calculation is revisited. By clarifying some
details in the residue evaluations, we find and correct some inaccuracies of
the previous result. The final result for contributions involving no more than
two particles in the intermediate states is presented. The result is verified
by proving a symmetry property which follows from the general structure of the
spectral expansion, and also by numerical comparison to the discrete finite
volume spectral sum. A further consistency check is performed by showing that
the expansion satisfies the cluster property up to the order of the evaluation.Comment: 38 pages, 1 eps figure
Overlap singularity and time evolution in integrable quantum field theory
We study homogeneous quenches in integrable quantum field theory where the
initial state contains zero-momentum particles. We demonstrate that the
two-particle pair amplitude necessarily has a singularity at the two-particle
threshold. Albeit the explicit discussion is carried out for special
(integrable) initial states, we argue that the singularity is inevitably
present and is a generic feature of homogeneous quenches involving the creation
of zero momentum particles. We also identify the singularity in quenches in the
Ising model across the quantum critical point, and compute it perturbatively in
phase quenches in the quantum sine-Gordon model which are potentially relevant
to experiments. We then construct the explicit time dependence of one-point
functions using a linked cluster expansion regulated by a finite volume
parameter. We find that the secular contribution normally linear in time is
modified by a term. We additionally encounter a novel type of secular
contribution which is shown to be related to parametric resonance. It is an
interesting open question to resum the new contributions and to establish their
consequences directly observable in experiments or numerical simulations.Comment: 30+45 pages, 7 figure
Rethinking Mackinder’s thoughts: The „Heartland”in the 21st century geopolitics
A klasszikus háború politológiai, politikai filozófiai és geopolitikai koncepciója a 19. századtól a 21. századig átértékelődött vagy átstrukturálódott. Mennyire alkalmazható, megvalósítható és adaptálható Halford John Mackinder „Heartland” elmélete a modern és premodern geopolitikai konfliktusok megoldásában? Hogyan értelmezhetők Mackinder gondolatai a mai modern politikatudományban és geopolitikában? Ezek a kérdések képzik tanulmányom lényegét
Rethinking Mackinder’s thoughts: The „Heartland”in the 21st century geopolitics
A klasszikus háború politológiai, politikai filozófiai és geopolitikai koncepciója a 19. századtól a 21. századig átértékelődött vagy átstrukturálódott. Mennyire alkalmazható, megvalósítható és adaptálható Halford John Mackinder „Heartland” elmélete a modern és premodern geopolitikai konfliktusok megoldásában? Hogyan értelmezhetők Mackinder gondolatai a mai modern politikatudományban és geopolitikában? Ezek a kérdések képzik tanulmányom lényegét
Optimal control of a large dam
A large dam model is an object of study of this paper. The parameters
and are its lower and upper levels,
is large, and if a current level of water is between
these bounds, then the dam is assumed to be in normal state. Passage one or
other bound leads to damage. Let denote the damage cost of
crossing the lower (upper) level. It is assumed that input stream of water is
described by a Poisson process, while the output stream is state-dependent (the
exact formulation of the problem is given in the paper). Let denote the
dam level at time , and let , exist. The
long-run average cost is a performance measure. The aim of
the paper is to choose the parameter of output stream (exactly specified in the
paper) minimizing .Comment: To appear in "Journal of Applied Probability" 44 (2007), No.
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