Results 1 - 10 of 7534
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[en] We evaluate the one-loop fermion self-energy for the gauged Thirring model in (2+1) dimensions, with one massive fermion flavor. We do this in the framework of the causal perturbation theory. In contrast to QED3, the corresponding two-point function turns out to be infrared finite on the mass shell. Then, by means of a Ward identity, we derive the on-shell vertex correction and discuss the role played by causality for non-renormalizable theories. (orig.)
[en] Energy shifts of radiative corrections in atoms due to perturbing potentials are calculated. The potentials considered are a constant magnetic field, the magnetic field of a nucleus, and the Coulomb interaction from other electrons in many-electron atoms. copyright 1997 The American Physical Society
[en] We present an infinite class of 2+1 dimensional field theories which, after coupling to semi-holographic fermions, exhibit strange metallic behavior in a suitable large N limit. These theories describe lattices of hypermultiplet defects interacting with parity-preserving supersymmetric Chern-Simons theories with U(N) x U(N) gauge groups at levels ±k. They have dual gravitational descriptions in terms of lattices of probe M2 branes in AdS4 x S7/Zk (for N >> 1,N >> k5) or probe D2 branes in AdS4 x CP3 (for N >> k >> 1,N << k5). We discuss several challenges one faces in maintaining the success of these models at finite N, including backreaction of the probes in the gravity solutions and radiative corrections in the weakly coupled field theory limit.
[en] We study aspects of the large-N volume independence on R3 X L#Gamma#, where L#Gamma# is a Γsite lattice for Yang-Mills theory with adjoint Wilson-fermions. We find the critical number of lattice sites above which the center-symmetry analysis on L#Gamma# agrees with the one on the continuum S1. For Wilson parameter set to one and Γ≥2, the two analyses agree. One-loop radiative corrections to Wilson-line masses are finite, reminiscent of the UV-insensitivity of the Higgs mass in deconstruction/Little-Higgs theories. Even for theories with Γ=1, volume independence in QCD(adj) may be guaranteed to work by tuning one low-energy effective field theory parameter. Within the parameter space of the theory, at most three operators of the 3d effective field theory exhibit one-loop UV-sensitivity. This opens the analytical prospect to study 4d non-perturbative physics by using lower dimensional field theories (d=3, in our example).
[en] The effective action for a non-stationary homogeneous electric field with arbitrary time dependence is found in the one-loop approximation. In the framework of the canonical formalism the correspondence is shown between the results obtained and the known expressions for the vacuum energy density. It is shown that for sufficiently weak and slowly varying electromagnetic fields the results agree with those of perturbation theory
[en] In field theories where a metastable false vacuum state arises as a result of radiative corrections, the calculation of the rate of false vacuum decay by bubble nucleation depends on the effective potential and the other functions that appear in the derivative expansion of the effective action. Beginning with the Nielsen identity, we derive a series of identities that govern the gauge dependence of these functions. Using these, we show, to leading nontrivial order, that, even though these functions are individually gauge dependent, one obtains a gauge-independent result for the bubble nucleation rate. Our formal arguments are complemented by explicit calculations for scalar electrodynamics in a class of Rξ gauges. copyright 1996 The American Physical Society
[en] In view of the smallness of the ratio of the electric to the magnetic γNδ coupling constants R=gE/gM ∼ O(10-2), of the order of radiative corrections, the validity of the standard unitarization procedure is investigated. The Fermi-Watson theorem is proven not to hold for the electric multipole with corrections to R of O(0.5x10-2). It is, moreover, pointed out that its application to Re E1+ does not allow a reliable determination of R which can come only from a direct measurement of Im E1+. Consideration of non-Watson-based experimental data yields an vertical bar R vertical bar definitively larger than 2x10-2. (author)
[en] A compact expression for one-loop radiative corrections to lepton lines in positronium and muonium hyperfine splitting is presented. It is valid for hyperfine-splitting contributions of order α2E/sub F/, including the effects of recoil to all orders. For muonium, known nonrecoil parts of this contribution are easily evaluated analytically, as is a previously calculated radiative-recoil contribution of order α2E/sub F/(m/sub e//m/sub μ/)ln(m/sub μ//m/sub e/). Nonlogarithmic radiative-recoil corrections obtained by numerical evaluation of this expression yield new contributions of 2.64 +- 0.07 kHz for muonium and -11.12 +- 0.02 MHz for positronium
[en] One of the most disturbing difficulties in thinking about the cosmological constant is that it is not stable under radiative corrections. The feedback mechanism proposed by Mukohyama and Randall is a dynamical way to protect a zero or small cosmological constant against radiative corrections.Hence, while this by itself does not solve the cosmological constant problem,it can help in solving the problem. In the present paper we investigate stability and gravity in this approach and show that the feedback mechanism is both classically and quantum mechanically stable and has self-consistent, stable dynamics