Search results for "Quantum electrodynamics."
showing 10 items of 797 documents
Low energy Quantum Gravity from the Effective Average Action
2010
Within the effective average action approach to quantum gravity, we recover the low energy effective action as derived in the effective field theory framework, by studying the flow of possibly non-local form factors that appear in the curvature expansion of the effective average action. We restrict to the one-loop flow where progress can be made with the aid of the non-local heat kernel expansion. We discuss the possible physical implications of the scale dependent low energy effective action through the analysis of the quantum corrections to the Newtonian potential.
Galilean Superconformal Symmetries
2009
We consider the non-relativistic c -> \infty contraction limit of the (N=2k)- extended D=4 superconformal algebra su(2,2;N), introducing in this way the non-relativistic (N=2k)-extended Galilean superconformal algebra. Such a Galilean superconformal algebra has the same number of generators as su(2,2|2k). The usp(2k) algebra describes the non-relativistic internal symmetries, and the generators from the coset u(2k)/usp(2k) become central charges after contraction.
Evolution of Mixed Dirac Particles Interacting with an External Magnetic Field
2007
We study in the framework of relativistic quantum mechanics the evolution of a system of two Dirac neutrinos that mix with each other and have non-vanishing magnetic moments. The dynamics of this system in an external magnetic field is determined by solving the Pauli-Dirac equation with a given initial condition. We consider first neutrino spin-flavor oscillations in a constant magnetic field and derive an analytical expression for the transition probability of spin-flavor conversion in the limit of small magnetic interactions. We then investigate ultrarelativistic neutrinos in an transversal magnetic field and derive their wave functions and transition probabilities with no limitation for …
Fermion masses and the UV cutoff of the minimal realistic SU(5)
2006
We investigate the predictions for fermion masses in the minimal realistic non-supersymmetric SU(5) model with the Standard Model matter content. The possibility to achieve b-\tau unification is studied taking into account all relevant effects. In addition, we show how to establish an upper bound on the ultraviolet cutoff \Lambda of the theory which is compatible with the Yukawa couplings at the grand unified scale and proton decay. We find \Lambda \simeq 10^{17} GeV, to be considered a conservative upper bound on the cutoff. We also provide up-to-date values of all the fermions masses at the electroweak scale.
On the Physical Propagators of QED
1993
The true variables in QED are the transverse photon components and Dirac's physical electron, constructed out of the fermionic field and the longitudinal components of the photon. We calculate the propagators in terms of these variables to one loop and demonstrate their gauge invariance. The physical electron propagator is shown not to suffer from infrared divergences in any gauge. In general, all physical Green's functions are gauge invariant and infrared-finite.
Short-distance contribution to the spectrum of Hawking radiation
2006
The Hawking effect can be rederived in terms of two-point functions and in such a way that it makes it possible to estimate, within the conventional semiclassical theory, the contribution of ultrashort distances to the Planckian spectrum. For Schwarzschild black holes of three solar masses the analysis shows that Hawking radiation is very robust up to frequencies of 96 T_H or 270 T_H for bosons and fermions, respectively. For primordial black holes (with masses around 10^{15} g) these frequencies turn out to be of order 52T_H and 142 T_H. Only at these frequencies and above do we find that the contribution of Planck distances is of order of the total spectrum itself. Below this scale, the c…
Low-energy scattering of extremal black holes by neutral matter
2002
We investigate the decay of a spherically symmetric near-extremal charged black hole, including back-reaction effects, in the near-horizon region. The non-locality of the effective action controlling this process allows and also forces us to introduce a complementary set of boundary conditions which permit to determine the asymptotic late time Hawking flux. The evaporation rate goes down exponentially and admits an infinite series expansion in Planck's constant. At leading order it is proportional to the total mass and the higher order terms involve higher order momenta of the classical stress-tensor. Moreover we use this late time behaviour to go beyond the near-horizon approximation and c…
Ramp-up of Hawking radiation in Bose-Einstein condensate analogue black holes
2020
Inspired by a recent experiment by Steinhauer and co-workers, we present a simple model which describes the formation of an acoustic black hole in a Bose-Einstein condensate, allowing an analytical computation of the evolution in time of the corresponding density-density correlator. We show the emergence of analog Hawking radiation out of a "quantum atmosphere" region significantly displaced from the horizon. This is quantitatively studied both at $T=0$ and even in the presence of an initial temperature T, as is always the case experimentally.
Testing Hawking particle creation by black holes through correlation measurements
2010
Hawking's prediction of thermal radiation by black holes has been shown by Unruh to be expected also in condensed matter systems. We show here that in a black hole-like configuration realized in a BEC this particle-creation does indeed take place and can be unambiguously identified via a characteristic pattern in the density-density correlations. This opens the concrete possibility of the experimental verification of this effect.
Superfield commutators for D = 4 chiral multiplets and their apppications
1987
The superfield commutators and their corresponding equal-time limits are derived in a covariant way for the D=4 free massive chiral multiplet. For interesting chiral multiplets, the general KAllen-Lehmann representation is also introduced. As applications of the free superfield commutators, the general solution of the Cauchy problem for chiral superfields is given, and an analysis of the closure of the bilinear products of superfields which desrcibe the extension of the internal currents for free supersymmetric chiral matter is performed.