31,034 research outputs found
Do the gravitational corrections to the beta functions of the quartic and Yukawa couplings have an intrinsic physical meaning?
We study the beta functions of the quartic and Yukawa couplings of General
Relativity and Unimodular Gravity coupled to the and Yukawa
theories with masses. We show that the General Relativity corrections to those
beta functions as obtained from the 1PI functional by using the standard MS
multiplicative renormalization scheme of Dimensional Regularization are gauge
dependent and, further, that they can be removed by a non-multiplicative,
though local, field redefinition. An analogous analysis is carried out when
General Relativity is replaced with Unimodular Gravity. Thus we show that any
claim made about the change in the asymptotic behaviour of the quartic and
Yukawa couplings made by General Relativity and Unimodular Gravity lack
intrinsic physical meaning.Comment: 6 pages, 7 figure
Unimodular Trees versus Einstein Trees
The maximally helicity violating (MHV) tree level scattering amplitudes
involving three, four or five gravitons are worked out in Unimodular Gravity.
They are found to coincide with the corresponding amplitudes in General
Relativity. This a remarkable result, insofar as both the propagators and the
vertices are quite different in both theories.Comment: 20 pages, 5 figure
Kinematic sensitivity to the Fierz term of -decay differential spectra
The current most stringent constraints on exotic scalar or tensor couplings
in neutron and nuclear decay, involving left-handed neutrinos, are
obtained from the Fierz interference term. The sensitivity to this term in a
correlation coefficient is usually driven by an energy-averaged kinematic
factor that increases monotonically toward smaller values of the
endpoint energies. We first point out here that this property does not hold for
certain differential observables that are directly sensitive to the Fierz term,
such as the or the recoil energy spectrum. This observation is relevant
for the selection of sensitive transitions in searches for exotic couplings
through spectrum shape measurements. We then point out previous errors in the
exploitation of measurements of the angular correlation coefficient
and discuss their impact on the extraction of constraints on exotic couplings.Comment: 7 pages, 5 figure
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