Search results for "Renormalization"
showing 10 items of 470 documents
One-loop effective lagrangian for an extension of the standard model with a heavy charged scalar singlet
1994
We study several problems related to the construction and the use of effective Lagrangians by considering an extension of the standard model that includes a heavy scalar singlet coupled to the leptonic doublet. Starting from the full renormalizable model, we build an effective field theory by integrating out the heavy scalar. A local effective Lagrangian (up to operators of dimension six) is obtained by expanding the one-loop effective action in inverse powers of the heavy mass. This is done by matching some Green functions calculated with both the full and the effective theories. Using this simple example we study the renormalization of effective Lagrangians in general and discuss how they…
Minimal supergravity radiative effects on the tri-bimaximal neutrino mixing pattern
2007
7 pages, 3 figures.-- PACS nrs.: 14.60.Pq, 12.60.Jv.-- ISI Article Identifier: 000245333000012.-- ArXiv pre-print available at: http://arxiv.org/abs/hep-ph/0606082
Unification of gauge couplings and the tau-neutrino mass in supergravity without R parity
1999
Minimal R-parity violating supergravity predicts a value for $alpha_s(M_Z)$ smaller than in the case with conserved R-parity, and therefore closer to the experimental world average. We show that the R-parity violating effect on the $alpha_s$ prediction comes from the larger two-loop b-quark Yukawa contribution to the renormalization group evolution of the gauge couplings which characterizes R-parity violating supergravity. The effect is correlated to the tau neutrino mass and is sensitive to the initial conditions on the soft supersymmetry breaking parameters at the unification scale. We show how a few percent effect on $alpha_s(M_Z)$ may naturally occur even with tau neutrino masses as sma…
Gluon spectrum in the glasma from JIMWLK evolution
2011
The JIMWLK equation with a "daughter dipole" running coupling is solved numerically starting from an initial condition given by the McLerran-Venugopalan model. The resulting Wilson line configurations are then used to compute the spectrum of gluons comprising the glasma inital state of a high energy heavy ion collision. The development of a geometrical scaling region makes the spectrum of produced gluons harder. Thus the ratio of the mean gluon transverse momentum to the saturation scale grows with energy. Also the total gluon multiplicity increases with energy slightly faster than the saturation scale squared.
Measurement of α from the structure of particle clusters produced in hadronic Z decays
1991
Abstract Using 106 000 hadronic events obtained with the ALEPH detector at LEP at energies close to the Z resonance peak, the strong coupling constant αs is measured by an analysis of energy-energy correlations (EEC) and the global event shape variables thrust, C-parameter and oblateness. It is shown that the theoretical uncertainties can be significantly reduced if the final state particles are first combined in clusters using a minimum scaled invariant mass cut, Ycut, before these variables are computed. The combined result from all shape variables of pre-clustered events is αs(MZ2 = 0.117±0.005 for a renormalization scale μ= 1 2 M Z . For μ values between MZ and the b-quark mass, the res…
Spin-dipole nuclear matrix elements for double beta decays and astro-neutrinos
2014
Spin-dipole (SD) nuclear matrix elements (NMEs) M±(SD2) for unique first forbidden β±2−→0+ ground-state-to-ground-state transitions are studied by using effective microscopic two-nucleon interactions in realistic single-particle model spaces. The observed values of the NMEs Mexp±(SD2) are compared with the values of the single-quasiparticle NMEs Mqp±(SD2) without nucleon spin–isospin (στ) correlation and the QRPA NMEs MQRPA±(SD2) with the στ correlation. The observed SD matrix elements are found to be reduced by the factor k≈0.2 with respect to Mqp±(SD2) and by the factor kNM≈0.5 with respect to MQRPA±(SD2). We then infer that the SD NME is reduced considerably partly by the nucleon στ corr…
The Pion Velocity in Dense Skyrmion Matter
2003
We have developed a field theory formalism to calculate $in$-$medium$ properties of hadrons within a unified approach that exploits a single Lagrangian to describe simultaneously both matter background and meson fluctuations. In this paper we discuss the consequences on physical observables of a possible phase transition of hadronic matter taking place in the chiral limit. We pay special attention to the pion velocity $v_\pi$, which controls, through a dispersion relation, the pion propagation in the hadronic medium. The $v_\pi$ is defined in terms of parameters related to the matrix element in matter of the axial-vector current, namely, the in-medium pion decay constants, $f_t$ and $f_s$. …
Nucleon-nucleon effective potential in dense matter including rho-meson exchange
1998
We obtain the RPA summed one-meson exchange potential between nucleons in symmetric nuclear matter at zero temperature, from a model which includes $\rho $, $\sigma $, $\omega $ and $\pi $ mesons. The behavior of rho mesons inside the medium is first discussed using different schemes to extract a finite contribution from the vacuum polarization. These schemes give qualitatively different results for the in-medium rho mass. The results are discussed in connection with the non-renormalizability of the model. We next study the modified potential as density increases. In the intermediate distance range, it is qualitatively modified by matter and vacuum effects. In the long-distance range ($r>2$…
Trilinear couplings and scalar bound states in supersymmetric extensions of the standard model
2001
Abstract The trilinear terms in minimal supersymmetric extensions of the standard model can be responsible of forming a bound state of scalars. In this talk we outline our results on the study of this bound state using a non-perturbative method, the exact renormalization group. We focus on the trilinear term between the Higgs and stop fields.
CORRELATIONS BETWEEN ε′/ε AND HEAVY TOP
1991
The paper reviews new theoretical developments for the CP-parameter ε′/ε and its intimate connection with the mass of a heavy top quark. It presents an extensive list of results and their implications for experiments.