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Search Results: 1 - 10 of 119037 matches for " Emil T. Akhmedov "
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Real or Imaginary? (On pair creation in de Sitter space)
Emil T. Akhmedov
Physics , 2009, DOI: 10.1142/S0217732310034043
Abstract: Using properly defined Feynman propagator we obtain non--zero imaginary contribution to the scalar field effective action in even dimensional de Sitter space. Such a propagator follows from the path integral in de Sitter space and obeys composition principle proposed in arXiv:0709.2899. The obtained expression for the effective action shows particle production with the Gibbons--Hawking rate.
Expansion in Feynman Graphs as Simplicial String Theory
Emil T. Akhmedov
Physics , 2004, DOI: 10.1134/1.1813675
Abstract: We show that the series expansion of quantum field theory in the Feynman diagrams can be explicitly mapped on the partition function of the simplicial string theory -- the theory describing embeddings of the two--dimensional simplicial complexes into the space--time of the field theory. The summation over two--dimensional geometries in this theory is obtained from the summation over the Feynman diagrams and the integration over the Schwinger parameters of the propagators. We discuss the meaning of the obtained relation and derive the one--dimensional analog of the simplicial theory on the example of the free relativistic particle.
Non-Abelian Structures in BSFT and RR couplings
Emil T. Akhmedov
Physics , 2001, DOI: 10.1063/1.1454352
Abstract: In this talk we show that the tachyon annihilation combined with an approximation, in which string theory non-commutativity structure is captured by the algebra of differential operators on space-time, gives a unified point of view on: non-Abelian structures on $D$-branes; all lowest energy excitations on $D$-branes; all RR couplings in type II string theory.
Towards the Theory of Non--Abelian Tensor Fields II
Emil T. Akhmedov
Mathematics , 2005,
Abstract: We go on with the definition of the theory of the non--Abelian two--tensor fields and find the gauge transformation rules and curvature tensor for them. To define the theory we use the surface {\it exponent} proposed in hep--th/0503234. We derive the differential equation for the {\it exponent} and make an attempt to give a matrix model formulation for it. We discuss application of our constructions to the Yang--Baxter equation for integrable models and to the String Field Theory.
A simple way to take into account back reaction on pair creation
Emil T. Akhmedov,Philipp Burda
Physics , 2009, DOI: 10.1016/j.physletb.2010.03.040
Abstract: We propose a simple and systematic way of accounting for the back reaction on the background field due to the pair creation in the four--dimensional scalar QED. This method is straightforwardly generalizable to the gravity backgrounds. In the case of QED with the instantly switched on constant electric field background we obtain a remarkably simple formula for its decay rate.
On the physical meaning of the Unruh effect
Emil T. Akhmedov,Douglas Singleton
Physics , 2007, DOI: 10.1134/S0021364007210138
Abstract: We present simple arguments that detectors moving with constant acceleration (even acceleration for a finite time) should detect particles. The effect is seen to be universal. Moreover, detectors undergoing linear acceleration and uniform, circular motion both detect particles for the same physical reason. We show that if one uses a circularly orbiting electron in a constant external magnetic field as the Unruh--DeWitt detector, then the Unruh effect physically coincides with the experimentally verified Sokolov--Ternov effect.
On the relation between Unruh and Sokolov--Ternov effects
Emil T. Akhmedov,Douglas Singleton
Physics , 2006, DOI: 10.1142/S0217751X07037081
Abstract: We show that the Sokolov--Ternov effect -- the depolarization of particles in storage rings coming from synchrotron radiation due to spin flip transitions -- is physically equivalent to the Unruh effect for circular acceleration if one uses a spin 1/2 particle as the Unruh--DeWitt detector. It is shown that for the electron, with gyromagnetic number $g \approx 2$, the exponential contribution to the polarization, which usually characterizes the Unruh effect, is "hidden" in the standard Sokolov-Ternov effect making it hard to observe. Thus, our conclusions are different in detail from previous work.
Interacting Field Theories in de Sitter Space are Non-Unitary
Akhmedov, Emil T.;Buividovich, P. V.
High Energy Physics - Phenomenology , 2008, DOI: 10.1103/PhysRevD.78.104005
Abstract: It is well known that there should be a total cancellation of the IR divergences in unitary interacting field theories, such as QED and gravity. The cancellation should be at all orders between loop and tree level contributions to cross--sections. This is the crucial fact related to the unitarity of the evolution operator (S--matrix) of the underlying interacting field theory. In this note we show that such a cancellation does {\it not} happen in de Sitter space.
Subtleties in the quasi-classical calculation of Hawking radiation
Emil T. Akhmedov,Terry Pilling,Douglas Singleton
Physics , 2008, DOI: 10.1142/S0218271808013947
Abstract: he quasi-classical method of deriving Hawking radiation is investigated. In order to recover the original Hawking temperature one must take into account a previously ignored contribution coming from the temporal part of the action. This contribution plus a contribution coming from the spatial part of the action gives the correct temperature.
Interacting Field Theories in de Sitter Space are Non-Unitary
Emil T. Akhmedov,P. V. Buividovich
Physics , 2008, DOI: 10.1103/PhysRevD.78.104005
Abstract: It is well known that there should be a total cancellation of the IR divergences in unitary interacting field theories, such as QED and gravity. The cancellation should be at all orders between loop and tree level contributions to cross--sections. This is the crucial fact related to the unitarity of the evolution operator (S--matrix) of the underlying interacting field theory. In this note we show that such a cancellation does {\it not} happen in de Sitter space.
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