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Andrzej Czarnecki

Publications and source records attributed to Andrzej Czarnecki.

At least 55 records · Page 3Linked to original sources
arXiv2016

Positronium Decay into a Photon and Neutrinos

We determine the rates and energy and angular distributions of the positronium decays into a photon and a neutrino-antineutrino pair, Ps-->gamma+nu+anti-nu. We find that both positronium spin states have access to this decay channel, contrary to a previously published result. The low-energy tails of the spectra are shown to be sensitive to the binding effects and agree with Low's theorem. Additionally, we find a connection between the behaviour of the soft photon spectrum in both o-Ps-->gamma+nu+anti-nu and o-Ps-->3gamma decays, and the Stark effect.

hep-ph↗
arXiv2016

On normality of f.pk-structures on g-manifolds

We consider higher dimensional generalisations of normal almost contact structures, the so called f.pk-structures where parallelism spans a Lie algebra g (f.pk-g-structures). Two types of these structures are discussed. In the first case, we construct an almost complex structure on a product manifold mirroring K-structures. We show that the natural normality condition can be satisfied only when g is abelian. The second case we consider is when the Lie algebra in question is 3-dimensional, but the almost complex structure on a product is constructed in a different manner. In both cases the normality conditions are expressed in terms of the structure tensors.

math.DG↗
arXiv2016

Bound muon decay spectrum in the leading logarithmic accuracy

We compute the dominant, logarithmically enhanced radiative corrections to the electron spectrum in the bound muon decay in the whole experimentally interesting range. The corrected spectrum fits well the TWIST results. The remaining theoretical error, dominated by the nuclear charge distribution, can be reduced in the muon-electron conversion searches by measuring the spectrum slightly below the New Physics signal window.

hep-ph↗
arXiv2015

High-energy electrons from the muon decay in orbit: radiative corrections

We determine the $\mathcal{O}(α)$ correction to the energy spectrum of electrons produced in the decay of muons bound in atoms. We focus on the high-energy end of the spectrum that constitutes a background for the muon-electron conversion and will be precisely measured by the upcoming experiments Mu2e and COMET. The correction suppresses the background by about 15\%.

hep-ph↗
arXiv2015

Shape function in QED and bound muon decays

When a particle decays in an external field, the energy spectrum of the products is smeared. We derive an analytical expression for the shape function accounting for the motion of the decaying particle and the final state interactions. We apply our result to calculate the muonium decay spectrum and comment on applications to the muon bound in an atom.

hep-ph↗
arXiv2015

Alexander-Spanier cohomology and boundary of a domain

We investigate a property: a domain cuts the ambient space if and only if it's boundary is disconnected. Previously, we had shown that for compact manifolds this property is equivalent to the manifold having trivial 1-cohomology. We now generalize this discussion to locally connected metric spaces.

math.GN↗
arXiv2015

Magnetic moment of the positronium ion and virial relations

We derive a hypervirial relation for the positronium ion, a three-body bound state of two electrons and a positron. It relates expectation values of three operators and reconciles two recently published, seemingly inequivalent formulas for the magnetic moment of the ion. As a by-product, the precision of the leading binding correction is improved.

hep-ph↗
arXiv2014

Michel decay spectrum for a muon bound to a nucleus

The spectrum of electrons from muons decaying in an atomic bound state is significantly modified by their interaction with the nucleus. Somewhat unexpectedly, its first measurement, at the Canadian laboratory TRIUMF, differed from basic theory. We show, using a combination of techniques developed in atomic, nuclear, and high-energy physics, that radiative corrections eliminate the discrepancy. In addition to solving that outstanding problem, our more precise predictions are potentially useful for interpreting future high-statistics muon experiments that aim to search for exotic interactions at $10^{-16}$ sensitivity.

hep-ph↗
arXiv2014

Anomalous magnetic moment of the positronium ion

We determine the gyromagnetic factor of the positronium ion, a three-body system consisting of two electrons and a positron, including first relativistic corrections. We find that the g-factor is modified by a term -0.51(1)alpha^2, exceeding 15 times the alpha^2 correction for a free electron. We compare this effect with analogous results found previously in atomic positronium and in hydrogen-like ions.

hep-ph↗
arXiv2014

Current distribution in an infinite plate

Distribution of the electric potential in a very long plate (for example a long metal ruler) is determined. This is achieved by conformally mapping the plate into a plane, simplifying the geometry of boundary conditions. Singularities of the potential are discussed as well as their regularization by the final size of electrical contacts. An analogy with renormalization is pointed out. Results are compared with previous studies.

physics.class-ph↗
arXiv2014

Muon decay spin asymmetry

We compute the spin asymmetry of the muon decay through O(alpha^2) in perturbative QED. These two-loop corrections are about a factor five (twenty) smaller than the current statistical (systematic) uncertainty of the most precise measurement, performed by the TWIST collaboration. We point out that at O(alpha^2) the asymmetry requires a careful definition due to multi-lepton final states and suggest to use familiar QCD techniques to define it in an infra-red safe way. We find that the TWIST measurement of the asymmetry is in excellent agreement with the Standard Model.

hep-ph↗
arXiv2012

Charged-Particle Decay at Finite Temperature

Radiative corrections to the decay rate of charged fermions caused by the presence of a thermal bath of photons are calculated in the limit when temperatures are below the masses of all charged particles involved. The cancellation of finite-temperature infrared divergences in the decay rate is described in detail. Temperature-dependent radiative corrections to a two-body decay of a hypothetical charged fermion and to electroweak decays of a muon are given. We touch upon possible implications of these results for charged particles in the early Universe.

hep-ph↗
arXiv2012

Binding energy of the positronium negative ion via dimensional scaling

We determine the binding energy of the negative positronium ion in the limits of one spatial dimension and of infinitely many dimensions. The numerical result for the one-dimensional ground state energy seems to be a rational number, suggesting the existence of an analytical solution for the wave function. We construct a perturbation expansion around the infinitely-dimensional limit to compute an accurate estimate for the physical three-dimensional case. That result for the energy agrees to five significant figures with variational studies.

hep-ph↗
arXiv2011

Bounds on majoron emission from muon to electron conversion experiments

In models where lepton number is considered to be a spontaneously-broken global symmetry a massless Goldstone boson, the majoron (J), appears. We describe a procedure to explore the muon-electron-majoron coupling using the results from mu-e conversion search experiments. To accomplish that, we determine how the energy spectrum of the muon decay into an electron and a majoron is modified by binding effects in a muonic atom. We find that the future mu-to-e conversion experiments may be able to produce bounds on the mu->eJ rate which are comparable with the present ones from direct searches.

hep-ph↗
arXiv2011

Photon-photon scattering: a tutorial

Long-established results for the low-energy photon-photon scattering, gamma gamma --> gamma gamma, have recently been questioned. We analyze that claim and demonstrate that it is inconsistent with experience. We demonstrate that the mistake originates from an erroneous manipulation of divergent integrals and discuss the connection with another recent claim about the Higgs decay into two photons. We show a simple way of correctly computing the low-energy gamma gamma scattering.

hep-ph↗
arXiv2011

Muon decay in orbit: spectrum of high-energy electrons

Experimental searches for lepton-flavor-violating coherent muon-to-electron conversion in the field of a nucleus, have been proposed to reach the unprecedented sensitivity of 10^(-16) - 10^(-18) per stopped muon. At that level, they probe new interactions at effective-mass scales well beyond 1000 TeV. However, they must contend with background from ordinary bound muon decay. To better understand the background-spectrum shape and rate, we have carried out a detailed analysis of Coulombic-bound-state muon decay, including nuclear recoil. Implications for future experiments are briefly discussed.

hep-ph↗