2,272 research outputs found
Constrained Differential Renormalization of Yang-Mills Theories
We renormalize QCD to one loop in coordinate space using constrained
differential renormalization, and show explicitly that the Slavnov-Taylor
identities are preserved by this method.Comment: LaTex, 13 pages with 2 ps figure
Gauge Invariance and the Pauli-Villars Regulator in Lorentz- and CPT-Violating Electrodynamics
We examine the nonperturbative structure of the radiatively induced
Chern-Simons term in a Lorentz- and CPT-violating modification of QED. Although
the coefficient of the induced Chern-Simons term is in general undetermined,
the nonperturbative theory appears to generate a definite value. However, the
CPT-even radiative corrections in this same formulation of the theory generally
break gauge invariance. We show that gauge invariance may yet be preserved
through the use of a Pauli-Villars regulator, and, contrary to earlier
expectations, this regulator does not necessarily give rise to a vanishing
Chern-Simons term. Instead, two possible values of the Chern-Simons coefficient
are allowed, one zero and one nonzero. This formulation of the theory therefore
allows the coefficient to vanish naturally, in agreement with experimental
observations.Comment: 8 page
Electroweak Precision Observables and the Unhiggs
We compute one-loop corrections to the S and T parameters in the Unhiggs
scenario. In that scenario, the Standard Model Higgs is replaced by a non-local
object, called the Unhiggs, whose spectral function displays a continuum above
the mass gap. The Unhiggs propagator has effectively the same UV properties as
the Standard Model Higgs propagator, which implies that loop corrections to the
electroweak precision observables are finite and calculable. We show that the
Unhiggs is consistent with electroweak precision tests when its mass gap is at
the weak scale; in fact, it then mimics a light SM Higgs boson. We also argue
that the Unhiggs, while being perfectly visible to electroweak precision
observables, is invisible to detection at LEP.Comment: 13 pages; v2: references added, discussion of production
cross-section expande
Wilsonian renormalisation of CFT correlation functions: Field theory
We examine the precise connection between the exact renormalisation group with local couplings and the renormalisation of correlation functions of composite operators in scale-invariant theories. A geometric description of theory space allows us to select convenient non-linear parametrisations that serve different purposes. First, we identify normal parameters in which the renormalisation group flows take their simplest form; normal correlators are defined by functional differentiation with respect to these parameters. The renormalised correlation functions are given by the continuum limit of correlators associated to a cutoff-dependent parametrisation, which can be related to the renormalisation group flows. The necessary linear and non-linear counterterms in any arbitrary parametrisation arise in a natural way from a change of coordinates. We show that, in a class of minimal subtraction schemes, the renormalised correlators are exactly equal to normal correlators evaluated at a finite cutoff. To illustrate the formalism and the main results, we compare standard diagrammatic calculations in a scalar free-field theory with the structure of the perturbative solutions to the Polchinski equation close to the Gaussian fixed point.This work has been supported by the Spanish MICINN project FPA
2013-47836-C3-2-P, the MINECO project FPA2016-78220-C3-1-P and by the European
Commission through the contract PITN-GA-2012-316704 (HIGGSTOOLS)
Ideas de profesores en formaciĂłn sobre la enseñanza de un tĂłpico cientĂfico, el mol y los cálculos quĂmicos
Un caso de interdisciplinariedad en TeorĂa de la contabilidad: Los cambios contables desde el enfoque cognitivo-linguĂstico
Impact of extra particles on indirect Z' limits
We study the possibility of relaxing the indirect limits on extra neutral
vector bosons by their interplay with additional new particles. They can be
systematically weakened, even below present direct bounds at colliders, by the
addition of more vector bosons and/or scalars designed for this purpose.
Otherwise, they appear to be robust.Comment: Latex 23 pages, 8 eps figures. Minor changes, version published in
Phys. Rev.
Failure of Gauge Invariance in the Nonperturbative Formulation of Massless Lorentz-Violating QED
We consider a Lorentz-violating modification to the fermionic Lagrangian of
QED that is known to produce a finite Chern-Simons term at leading order. We
compute the second order correction to the one-loop photon self-energy in the
massless case using an exact propagator and a nonperturbative formulation of
the theory. This nonperturbative theory assigns a definite value to the
coefficient of the induced Chern-Simons term; however, we find that the theory
fails to preserve gauge invariance at higher orders. We conclude that the
specific nonperturbative value of the Chern-Simons coefficient has no special
significance.Comment: 8 pages, very minor change
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