arXiv subjects

Johan Relefors

Publications and source records attributed to Johan Relefors.

8 recordsLinked to original sources

arXiv2017

Vector two-point functions in finite volume using partially quenched chiral perturbation theory

We calculate vector-vector correlation functions at two loops using partially quenched chiral perturbation theory including finite volume effects and twisted boundary conditions. We present expressions for the flavor neutral cases and the flavor charged case with equal masses. Using these expressions we give an estimate for the ratio of disconnected to connected contributions for the strange part of the electromagnetic current. We give numerical examples for the effects of partial quenching, finite volume and twisting and suggest the use of different twists to check the size of finite volume effects. The main use of this work is expected to be for lattice QCD calculations of the hadronic vacuum polarization contribution to the muon anomalous magnetic moment.

hep-lat↗

arXiv2017

Twisted finite-volume corrections to $K_{l3}$ decays with partially-quenched and rooted-staggered quarks

The determination of $|V_{us}|$ from kaon semileptonic decays requires the value of the form factor $f_+(q^2=0)$ which can be calculated precisely on the lattice. We provide the one-loop partially quenched chiral perturbation theory expressions both with and without including the effects of staggered quarks for all form factors at finite volume and with partially twisted boundary conditions for both the vector current and scalar density matrix elements at all $q^2$. We point out that at finite volume there are more form factors than just $f_+$ and $f_-$ for the vector current matrix element but that the Ward identity is fully satisfied. The size of the finite-volume corrections at present lattice sizes is small. This will help improve the lattice determination of $f_+(q^2=0)$ since the finite-volume error is the dominant error source for some calculations. The size of the finite-volume corrections may be estimated on a single lattice ensemble by comparing results for various twist choices.

hep-lat↗

arXiv2016

Chiral Perturbation Theory at Finite Volume and/or with Twisted Boundary Conditions

In this talk we discuss a number of ChPT calculations relevant for lattice QCD. These include the finite volume corrections at two-loop order for masses and decay constants. The second part is about hadronic vacuum polarization where we present the two-loop ChPT estimate for the disconnected and strange quark contributions. We also present the finite volume corrections at two-loop order. The final part is the one-loop finite volume with twisted boundary conditions contribution to $f_+(q^2)$ and the full $K_{\ell3}$ amplitude

hep-lat↗

arXiv2016

Connected, Disconnected and Strange Quark Contributions to HVP

We calculate all neutral vector two-point functions in Chiral Perturbation Theory (ChPT) to two-loop order and use these to estimate the ratio of disconnected to connected contributions as well as contributions involving the strange quark. We extend the ratio of $-1/10$ derived earlier in two flavour ChPT at one-loop order to a large part of the higher order contributions and discuss corrections to it. Our final estimate of the ratio disconnected to connected is negative and a few % in magnitude.

hep-lat↗

arXiv2016

Pion light-by-light contributions to the muon $g-2$

This paper contains some new results on the hadronic light-by-light contribution (HLbL) to the muon $g-2$. The first part argues that we can expect large effects from disconnected diagrams in present and future calculations by lattice QCD of HLbL. The argument is based on the dominance of pseudo-scalar meson exchange. In the second part, we revisit the pion loop HLbL contribution to the muon anomalous magnetic moment. We study it in the framework of some models studied earlier, pure pion loop, full VMD and hidden local symmetry for inclusion of vector mesons. In addition we study possible ways to include the axial-vector meson. The main part of the work is a detailed study of how the different momentum regions contribute. We derive a short distance constraint on the $γ^*γ^*\toππ$ amplitude and use this as a constraint on the models used for the pion loop. As a byproduct we present the general result for integration using the Gegenbauer polynomial method.

hep-ph↗

arXiv2016

Masses, decay constants and electromagnetic form-factors with twisted boundary conditions

We discuss some of the effects of twisted boundary conditions in finite volume using continuum SU(3) Chiral Perturbation Theory. We point out how broken cubic symmetry affects the definitions of quantities such as form-factors. Using the $π^+$ as an example, we give one loop results for the mass, decay constants and electromagnetic form-factor and illustrate how the relevant Ward identities are satisfied.

hep-lat↗

arXiv2014

Masses, Decay Constants and Electromagnetic Form-factors with Twisted Boundary Conditions

Using Chiral Perturbation Theory at one-loop we analyze the consequences of twisted boundary conditions. We point out that due to the broken Lorentz and reflection symmetry a number of unexpected terms show up in the expressions. We explicitly discuss the pseudo-scalar octet masses, axial-vector and pseudo-scalar decay constants and electromagnetic form-factors. We show how the Ward identities are satisfied using the momentum dependent masses and the non-zero vacuum-expectation-values values for the electromagnetic (vector) currents. Explicit expressions at one-loop are provided and an appendix discusses the needed one-loop twisted finite volume integrals.

hep-lat↗

arXiv2012

A Study of Heavy Higgs Properties at a Multi-TeV e+e- Collider

The precise determination of the masses of the neutral and charged heavy Higgs bosons is a crucial input for the study of Supersymmetry and its relation with cosmology through dark matter. This paper presents a study of e+e- -> HA and H+H- production at sqrts=3 TeV. The analysis is performed with full simulation and reconstruction accounting for beamstrahlung effects and the overlay of gamma gamma -> hadrons events. Results are presented in terms of the accuracy on the determination of the masses and widths of the heavy Higgs bosons in two benchmark scenarios.

hep-ex↗