[Seminar] Colloquium - Tuesday March 6th 2007

[Marco Cavaglia]

Hello!

Next Tuesday (March 6th) two of our brightest graduate students will give 
two mini-colloquia: 

Chris Maggio will speak of

Estimations of Charge Transfer By Lightning Flashes

A lightning flash transfers charge between in-cloud charge regions or 
between in-cloud charge regions and the ground. Previous studies to 
determine the location and magnitude of this charge transfer were made by 
measuring the electric field change due to a lightning flash. These 
measurements were taken using either a ground field mill network or a 
network of flat plate antennas operating as electric field change sensors. 
Point charges or point dipoles were used to match the electric field 
change at the ground, however these estimates were made with no knowledge 
of where the lightning flash actually propagated. The recent development 
of the Lightning Mapping Array (LMA) has solved this problem. In this 
presentation we use the LMA, along with in-cloud balloon and ground field 
mill E-field measurements, to model the charge transfer along the actual 
path of the lightning flash. We also combine the results of the charge 
transfer models to in-cloud measurements of the voltage differences 
between charge regions to determine the amount of work done by the 
lightning flash.

Arunava Roy will speak of

Roy on Cosmic Rays

One way to solve the hierarchy problem of particle physics is to introduce
large extra dimensions (LED). As suggested by the Arkani-Hamed,
Dimopoulos, and Dvali (ADD) theory these LED could be of the order of few
microns (and even smaller as the number of dimension increases). Therefore
physical systems would go from a regime of weak gravity at large distances
to one where gravity is strong at small distances. If the fundamental
scale of gravity is of the order of a few TeV then particle colliders
(e.g. the Large Hadron Collider, LHC) could produce BH's. UHECR's (with
center of mass energy > 100 TeV) provide a natural means of producing such
high-energy particles. Cosmogenic neutrinos could be able to produce BH?s
in the atmosphere via neutrino-quark interactions. Interest in this is
also generated by the fact that there are neutrino searches from
experiments such as Ice Cube, GLAST etc. We analyze such BH signatures so
as to be able to distinguish them from SM processes. These would enable us
to predict (at least theoretically) if we would be able to detect such
BH?s at the LHC or the Pierre Auger Observatory. Effects of rotation would
also be discussed.

The talks begin at 4:00 in Lewis 101 with refreshments 15 minutes before.
Attendance is mandatory for all graduate students (specially Chris and
Arunava).

Cheers,
Marco