34,356 research outputs found
Rare top decay t-> c l+l- as a probe of new physics
The rare top decay t-> c l+l-, which involves flavor violation, is studied as
a possible probe of new physics. This decay is analyzed with the simplest
Standard Model extensions with additional gauge symmetry formalism. The
considered extension is the Left-Right Symmetric Model, including a new neutral
gauge boson Z' that allows to obtain the decay at tree level through Flavor
Changing Neutral Currents (FCNC) couplings. The neutral gauge boson couplings
are considered diagonal but family non-universal in order to induce these FCNC.
We find the $BR(t-> c l+l-)~10^{-13} for a range 1 TeV < M_{Z'} < 3 TeV.Comment: 9 pages, 6 figure
Moments of inertia for solids of revolution and variational methods
We present some formulae for the moments of inertia of homogeneous solids of
revolution in terms of the functions that generate the solids. The development
of these expressions exploits the cylindrical symmetry of these objects, and
avoids the explicit use of multiple integration, providing an easy and
pedagogical approach. The explicit use of the functions that generate the solid
gives the possibility of writing the moment of inertia as a functional, which
in turn allows us to utilize the calculus of variations to obtain a new insight
into some properties of this fundamental quantity. In particular, minimization
of moments of inertia under certain restrictions is possible by using
variational methods.Comment: 6 pages, 6 figures, LaTeX2e. Two paragraphs added. Minor typos
corrected. Version to appear in European Journal of Physic
Nuclear Activity in Circumnuclear Ring Galaxies
We have analyzed the frequency and properties of the nuclear activity in a
sample of galaxies with circumnuclear rings and spirals (CNRs). This sample was
compared with a control sample of galaxies with very similar global properties
but without circumnuclear rings. We discuss the relevance of the results in
regard to the AGN feeding processes and present the following results: (i)
bright companion galaxies seem not to be important for the appearance of CNRs,
which appear to be more related to intrinsic properties of the host galaxies or
to minor merger processes; (ii) the proportion of strong bars in galaxies with
an AGN and a CNR is somewhat higher than the expected ratio of strongly barred
AGN galaxies from the results of Ho and co-workers; (iii) the incidence of
Seyfert activity coeval with CNRs is clearly larger than the rate expected from
the morphological distribution of the host galaxies; (iv) the rate of Sy 2 to
Sy 1 type galaxies with CNRs is about three times larger than the expected
ratio for galaxies without CNRs and is opposite to that predicted by the
geometric paradigm of the classical unified model for AGNs, although it does
support the hy-pothesis that Sy 2 activity is linked to circumnuclear star
formation. The possible selection effects of the sample are discussed, and we
conclude that the detected trends are strong enough to justify high quality
observations of as large as possible sets of galaxies with circumnuclear rings
and their matched control samples.Comment: Submitted to International Journal of Astronomy and Astrophysic
- …