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Papers by Karim Salehi
Journal of Physics A-mathematical and Theoretical, 2007
We calculate dilaton and axion radiation generated in the collision of two straight initially une... more We calculate dilaton and axion radiation generated in the collision of two straight initially unexcited strings and give a rough cosmological estimate of dilaton and axion densities produced via this mechanism in the early universe.
Physical Review D, 2007
We study Cerenkov radiation from moving straight strings which slide with respect to each other i... more We study Cerenkov radiation from moving straight strings which slide with respect to each other in such a way that the projected intersection point moves faster than light. To calculate this effect we develop classical perturbation theory for the system of Nambu-Goto strings interacting with the dilaton, two-form, and gravity fields. In the first order, one encounters divergent self-action terms which are eliminated by classical renormalization of the string tension. Cerenkov radiation arises in the second order. It is generated by an effective source which contains contributions localized on the string world sheets and bulk contributions quadratic in the first-order fields. In the ultrarelativistic limit radiation exhibits angular peaking on the Cerenkov cone in the forward direction of the fast string in the rest frame of another. The radiation spectrum then extends up to high frequencies proportional to the square of the Lorentz factor of the relative velocity. Gravitational radiation is absent since the 1+2 space-time transverse to the straight string does not allow for gravitons. A rough estimate of the Cerenkov radiation in the cosmological cosmic strings network is presented.
Journal of Physics A-mathematical and General, 2007
We calculate dilaton and axion radiation generated in the collision of two straight initially une... more We calculate dilaton and axion radiation generated in the collision of two straight initially unexcited strings and give a rough cosmological estimate of dilaton and axion densities produced via this mechanism in the early universe.
We consider Cerenkov radiation which must arise when randomly oriented straight cosmic (super)str... more We consider Cerenkov radiation which must arise when randomly oriented straight cosmic (super)strings move with relativistic velocities without intercommutation. String interactions via dilaton, two-form and gravity (gravity being the dominant force in the ultra-relativistic regime) leads to formation of superluminal sources which generate Cerenkov radiation of dilatons and axions. Though the effect is of the second order in the couplings of strings to these fields, its total efficiency is increased by high dependence of the radiation rate on the Lorentz-factor of the collision.
Physical Review D, 2007
We study Cerenkov radiation from moving straight strings which glisse with respect to each other ... more We study Cerenkov radiation from moving straight strings which glisse with respect to each other in such a way that the projected intersection point moves faster than light. To calculate this effect we develop classical perturbation theory for the system of Nambu-Goto strings interacting with dilaton, two-form and gravity. In the first order one encounters divergent self-action terms which are eliminated by classical renormalization of the string tension. Cerenkov radiation arises in the second order. It is generated by an effective source which contains contributions localized on the strings world-sheets and bulk contributions quadratic in the first order fields. In the ultra-relativistic limit radiation exhibits angular peaking on the Cerenkov cone in the forward direction of the fast string in the rest frame of another. The radiation spectrum then extends up to high frequencies proportional to square of the Lorentz-factor of the relative velocity. Gravitational radiation is absent since the 1+2 space-time transverse to the straight string does not allow for gravitons. A rough estimate of the Cerenkov radiation in the cosmological cosmic strings network is presented.
We consider Cerenkov radiation which must arise when randomly oriented straight cosmic (super)str... more We consider Cerenkov radiation which must arise when randomly oriented straight cosmic (super)strings move with relativistic velocities without intercommutation. String interactions via dilaton, two-form and gravity (gravity being the dominant force in the ultra-relativistic regime) leads to formation of superluminal sources which generate Cerenkov radiation of dilatons and axions. Though the effect is of the second order in the couplings of strings to these fields, its total efficiency is increased by high dependence of the radiation rate on the Lorentz-factor of the collision.
We calculate classically the radiation of the antisymmetric form field generated in the collision... more We calculate classically the radiation of the antisymmetric form field generated in the collision of two non-excited membranes moving with ultrarelativistic velocities in five space-time dimensions. The interaction between branes through the form field is treated perturbatively with the deflection angle as a small parameter. Radiation arises in the second order approximation when the manifold of the minimal separation between the branes moves with the superluminal velocity. It exhibits typical Cherenkov cone features. Generalization to p-branes colliding in D = p + 3 dimensions is straightforward.
Journal of Physics A-mathematical and Theoretical, 2007
We calculate dilaton and axion radiation generated in the collision of two straight initially une... more We calculate dilaton and axion radiation generated in the collision of two straight initially unexcited strings and give a rough cosmological estimate of dilaton and axion densities produced via this mechanism in the early universe.
Physical Review D, 2007
We study Cerenkov radiation from moving straight strings which slide with respect to each other i... more We study Cerenkov radiation from moving straight strings which slide with respect to each other in such a way that the projected intersection point moves faster than light. To calculate this effect we develop classical perturbation theory for the system of Nambu-Goto strings interacting with the dilaton, two-form, and gravity fields. In the first order, one encounters divergent self-action terms which are eliminated by classical renormalization of the string tension. Cerenkov radiation arises in the second order. It is generated by an effective source which contains contributions localized on the string world sheets and bulk contributions quadratic in the first-order fields. In the ultrarelativistic limit radiation exhibits angular peaking on the Cerenkov cone in the forward direction of the fast string in the rest frame of another. The radiation spectrum then extends up to high frequencies proportional to the square of the Lorentz factor of the relative velocity. Gravitational radiation is absent since the 1+2 space-time transverse to the straight string does not allow for gravitons. A rough estimate of the Cerenkov radiation in the cosmological cosmic strings network is presented.
Journal of Physics A-mathematical and General, 2007
We calculate dilaton and axion radiation generated in the collision of two straight initially une... more We calculate dilaton and axion radiation generated in the collision of two straight initially unexcited strings and give a rough cosmological estimate of dilaton and axion densities produced via this mechanism in the early universe.
We consider Cerenkov radiation which must arise when randomly oriented straight cosmic (super)str... more We consider Cerenkov radiation which must arise when randomly oriented straight cosmic (super)strings move with relativistic velocities without intercommutation. String interactions via dilaton, two-form and gravity (gravity being the dominant force in the ultra-relativistic regime) leads to formation of superluminal sources which generate Cerenkov radiation of dilatons and axions. Though the effect is of the second order in the couplings of strings to these fields, its total efficiency is increased by high dependence of the radiation rate on the Lorentz-factor of the collision.
Physical Review D, 2007
We study Cerenkov radiation from moving straight strings which glisse with respect to each other ... more We study Cerenkov radiation from moving straight strings which glisse with respect to each other in such a way that the projected intersection point moves faster than light. To calculate this effect we develop classical perturbation theory for the system of Nambu-Goto strings interacting with dilaton, two-form and gravity. In the first order one encounters divergent self-action terms which are eliminated by classical renormalization of the string tension. Cerenkov radiation arises in the second order. It is generated by an effective source which contains contributions localized on the strings world-sheets and bulk contributions quadratic in the first order fields. In the ultra-relativistic limit radiation exhibits angular peaking on the Cerenkov cone in the forward direction of the fast string in the rest frame of another. The radiation spectrum then extends up to high frequencies proportional to square of the Lorentz-factor of the relative velocity. Gravitational radiation is absent since the 1+2 space-time transverse to the straight string does not allow for gravitons. A rough estimate of the Cerenkov radiation in the cosmological cosmic strings network is presented.
We consider Cerenkov radiation which must arise when randomly oriented straight cosmic (super)str... more We consider Cerenkov radiation which must arise when randomly oriented straight cosmic (super)strings move with relativistic velocities without intercommutation. String interactions via dilaton, two-form and gravity (gravity being the dominant force in the ultra-relativistic regime) leads to formation of superluminal sources which generate Cerenkov radiation of dilatons and axions. Though the effect is of the second order in the couplings of strings to these fields, its total efficiency is increased by high dependence of the radiation rate on the Lorentz-factor of the collision.
We calculate classically the radiation of the antisymmetric form field generated in the collision... more We calculate classically the radiation of the antisymmetric form field generated in the collision of two non-excited membranes moving with ultrarelativistic velocities in five space-time dimensions. The interaction between branes through the form field is treated perturbatively with the deflection angle as a small parameter. Radiation arises in the second order approximation when the manifold of the minimal separation between the branes moves with the superluminal velocity. It exhibits typical Cherenkov cone features. Generalization to p-branes colliding in D = p + 3 dimensions is straightforward.