Search results for "effective field theory"
showing 10 items of 212 documents
Electromagnetism in nonleptonic weak interactions
2000
16 páginas, 1 figura.-- PACS: 11.30.Rd; 13.25.Es; 13.40.Ks.-- arXiv:hep-ph/0006172v2
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…
Beyond the dark matter effective field theory and a simplified model approach at colliders
2016
Direct detection of and LHC search for the singlet fermion dark matter (SFDM) model with Higgs portal interaction are considered in a renormalizable model where the full Standard Model (SM) gauge symmetry is imposed by introducing a singlet scalar messenger. In this model, direct detection is described by an effective operator m_q \bar{q} q \bar{\chi} \chi as usual, but the full amplitude for monojet + \not E_T involves two intermediate scalar propagators, which cannot be seen within the effective field theory (EFT) or in the simplified model without the full SM gauge symmetry. We derive the collider bounds from the ATLAS monojet + \not E_T as well as the CMS t\bar{t} + \not E_T data, findi…
Isospin dependence of the three-nucleon force
2004
We classify $A$--nucleon forces according to their isospin dependence and discuss the most general isospin structure of the three--nucleon force. We derive the leading and subleading isospin--breaking corrections to the three--nucleon force using the framework of chiral effective field theory.
Anomalous Higgs–top-quark couplings in the MSSM
2004
The anomalous couplings of the top quark and the Higgs boson have been studied in an effective theory deduced from the minimal supersymmetric extension of the standard model as the heavy fields are integrated out. Constraints on the parameters of the model from the experimental data of ${R}_{b}=\ensuremath{\Gamma}(\stackrel{\ensuremath{\rightarrow}}{Z}b\overline{b})/\ensuremath{\Gamma}(\stackrel{\ensuremath{\rightarrow}}{Z}\mathrm{hadrons})$ are obtained.
Top-quark phenomenology in models with bilinearly and spontaneously broken R-parity
1999
We study unconventional decays of the top-quark in the framework of SUSY models with spontaneously broken R-parity. In particular we discuss an effective theory which consists of the MSSM plus bilinearly broken R-parity. We demonstrate that the decay modes t -> stau + b and t -> tau + sbottom can have large branching ratios even in scenarios where the tau-neutrino mass is very small. We show that existing Tevatron data already probe the theoretical parameters, with promising prospects for further improvement at the Run 2 of the Tevatron.
Top-Quark Pair Production Beyond Next-to-Leading Order
2010
We report on recent calculations of the differential cross section for top-quark pair production at hadron colliders. The results are differential with respect to the top-pair invariant mass and to the partonic scattering angle. In these calculations, which were carried out by employing soft-collinear effective theory techniques, we resummed threshold logarithms up to next-to-next-to-leading logarithmic order. Starting from the differential cross section, it is possible to obtain theoretical predictions for the invariant-mass distribution and the total cross section. We summarize here our results for these observables, and we compare them with the results obtained from different calculation…
Can power corrections be reliably computed in models with extra dimensions?
2003
We critically revisit the issue of power-law running in models with extra dimensions. The analysis is carried out in the context of a higher-dimensional extension of QED, with the extra dimensions compactified on a torus. It is shown that a naive $\beta$ function, which simply counts the number of modes, depends crucially on the way the thresholds of the Kaluza-Klein modes are crossed. To solve these ambiguities we turn to the vacuum polarization, which, due to its special unitarity properties, guarantees the physical decoupling of the heavy modes. This latter quantity, calculated in the context of dimensional regularization, is used for connecting the low energy gauge coupling with the cou…
Role of Chiral Two-Body Currents in Li6 Magnetic Properties in Light of a New Precision Measurement with the Relative Self-Absorption Technique
2021
A direct measurement of the decay width of the excited ${0}_{1}^{+}$ state of $^{6}\mathrm{Li}$ using the relative self-absorption technique is reported. Our value of ${\mathrm{\ensuremath{\Gamma}}}_{\ensuremath{\gamma},{0}_{1}^{+}\ensuremath{\rightarrow}{1}_{1}^{+}}=8.17(14{)}_{\mathrm{stat}.}(11{)}_{\mathrm{syst}.}\text{ }\text{ }\mathrm{eV}$ provides sufficiently low experimental uncertainties to test modern theories of nuclear forces. The corresponding transition rate is compared to the results of ab initio calculations based on chiral effective field theory that take into account contributions to the magnetic dipole operator beyond leading order. This enables a precision test of the im…
Effective theories of flavor and the nonuniversal MSSM
2016
Flavor symmetries \`{a} la Froggatt-Nielsen~(FN) provide a compelling way to explain the hierarchies of fermionic masses and mixing angles in the Yukawa sector. In Supersymmetric~(SUSY) extensions of the Standard Model where the mediation of SUSY breaking occurs at scales larger than the breaking of flavor, this symmetry must be respected not only by the Yukawas of the superpotential, but by the soft-breaking masses and trilinear terms as well. In this work we show that contrary to naive expectations, even starting with completely flavor blind soft-breaking in the full theory at high scales, the low-energy sfermion mass matrices and trilinear terms of the effective theory, obtained upon int…