Motion of distant objects in the Universe

We give a brief survey of investigations of the structure of the Universe and of its expansion, for educational purposes. As we know it today, the size of the Universe is immense, enormous numbers of galaxies have been found in it, and in each galaxy enormous numbers of stars. The galaxies move from us at very high speeds, some of the more distant ones at speeds comparable to the velocity of light. Many theories have been developed to explain the vast amount of data that have been obtained by astronomical observations. We give a simplified theory of the cosmic expansion and present results of three models for the cosmic scale function R(t): the constant rate of expansion, the accelerated expansion and the constant Hubble parameter models

Charged LFV in a low-scale seesaw mSUGRA model

We investigate the influence of the boundary conditions of minimal supergravity (mSUGRA) on the supersymmetric mechanism for lepton flavour violation (LFV) proposed recently [1], within the framework of the MSSM extended by TeV-scale singlet heavy neutrinos. We find that the consideration of the mSUGRA boundary condition may increase the branching ratios of the muon and tauon decaying into three charged leptons by up to a factor of 5, whereas the corresponding branching ratio for their photonic decays remains almost unchanged.Comment: 6 pages, 3 figures. Prepared for the Proceedings of the 11th International Workshop on Tau Lepton Physics, Manchester, UK, September 13-17, 2010. Presented by A. Ilakova

Single-point observation of rapidly moving objects

We study the kinematical problem of observation of motion of objects that move at velocities comparable to the velocity of signals which are used to determine the velocity and distance of the objects. The main purpose of this work is to demonstrate the importance of time delay between the emission of signals and their reception at the observation point. The simplest cases are considered, i.e., rectilinear motion and assuming the observational point at the path of the moving object. Sound and light signals are considered to transmit the information on the motion. The results relating to the motion at constant velocity and for the acceleration due to a constant force are presented

Lepton flavor violation in the standard model extended by heavy singlet Dirac neutrinos

Low-energy neutrinoless lepton flavor-violating (LFV) processes are studied in an extension of the standard model (SM) by heavy SU(2)×U(1) singlet Dirac neutrinos. An upper-bound procedure is elaborated for the evaluation of amplitudes. A comment on the extraction of heavy-neutrino mixings from astrophysical observations is given. For processes not treated in the model applied, the formalism for evaluating the branching ratios (BR’s) is presented. The processes previously studied in the model are examined and some results are improved. The structure of the amplitudes and BR’s as well as the relations between BR’s of different LFV processes are examined. The decoupling of heavy neutrinos is discussed and it is explicitly shown that very heavy neutrinos decouple when the upper-bound procedure is applied. The LFV decays are shown to be unsuitable for finding upper bounds on “diagonal” LFV parameters. Comparing the theoretical BR’s with curent experimental upper bounds, a few processes interesting for the search for LFV are proposed. Particularly, B-meson LFV processes are suggested for the search of LFV in future B factories

Motion of distant objects in the Universe

We give a brief survey of investigations of the structure of the Universe and of its expansion, for educational purposes. As we know it today, the size of the Universe is immense, enormous numbers of galaxies have been found in it, and in each galaxy enormous numbers of stars. The galaxies move from us at very high speeds, some of the more distant ones at speeds comparable to the velocity of light. Many theories have been developed to explain the vast amount of data that have been obtained by astronomical observations. We give a simplified theory of the cosmic expansion and present results of three models for the cosmic scale function R(t): the constant rate of expansion, the accelerated expansion and the constant Hubble parameter models

Charged Lepton Flavour Violation in Supersymmetric Low-Scale Seesaw Models

We study charged lepton flavour violation in low-scale seesaw models of minimal supergravity, which realize large neutrino Yukawa couplings thanks to approximate lepton-number symmetries. There are two dominant sources of lepton flavour violation in such models. The first source originates from the usual soft supersymmetry-breaking sector, whilst the second one is entirely supersymmetric and comes from the supersymmetric neutrino Yukawa sector. Within the framework of minimal supergravity, we consider both sources of lepton flavour violation, soft and supersymmetric, and calculate a number of possible lepton-flavour-violating transitions, such as the photonic decays of muons and taus, mu -> e gamma, tau -> e gamma and tau -> mu gamma, their neutrinoless three-body decays, mu -> e e e, tau -> e e e, tau -> mu mu mu, tau -> e e mu and tau -> e mu mu, and the coherent mu -> e conversion in nuclei. After taking into account the exclusion bounds placed by present experiments of lepton flavour violation, we derive combined theoretical limits on the universal heavy Majorana mass scale mN and the light-to-heavy neutrino mixings. Supersymmetric low-scale seesaw models offer distinct correlated predictions for lepton-flavour-violating signatures, which might be discovered in current and projected experiments, such as MEG, COMET/PRISM, Mu2e, super-BELLE and LHCb.Comment: 28 pages, 11 figures, comment added to conclusions, version as to appear in Physical Review

Comment on "the decoupling of heavy sneutrinos in low-scale seesaw models"

The authors of a recent communication [arXiv:1312.5318] claim to have traced an error in the existing literature regarding the evaluation of the one-loop right-handed sneutrino contributions to lepton-flavour-violating observables in supersymmetric low-scale seesaw models. In this short note, we emphasize that contrary to those authors' claim, our paper [arXiv:1212.5939] contains no such a flaw, and both our analytical and numerical results exhibit the expected decoupling property of the heavy sneutrinos in the Z-penguin graphs.Comment: 2 pages, 1 figur

Lepton-flavor violation in light hadron decays

The lepton-flavor-violating decays of light pseudoscalar mesons and light baryons are investigated within extensions of the SU(2)×U(1) model. These models contain heavy Dirac or Majorana neutrinos and allow large lepton–heavy-neutrino mixings. The free-parameter space of these models is carefully studied. Special care is devoted to the comparison of results of different models. A large “nondecoupling” window is found, and the decoupling of extremely heavy neutrinos is explicitly shown in all models except one, for which the free-parameter space is bounded. Among the decays studied, the experimentally most interesting decays are KL→eμ and π0→eμ. The π0→eμ decay is found to be equally interesting for the study of lepton-flavor violation as KL→eμ decay. The constraint on the model parameters, coming from the nonobservation of the μ⃗ eγ decay, leads to the maximal decay rates B(KL→eμ)∼5×10-16 and B(π0→eμ)≲(2nR-2)×10-15, where nR is number of heavy neutrinos, much smaller than the present experimental upper limits