January 28, 2008
Speaker: Professor Michael Creutz, BNL
Title: Four-dimensional graphene and chiral fermions
Abstract:
Motivated by the description of the graphene electronic structure in
terms of the relativistic Dirac equation, a generalization to four dimensions yields a strictly local fermion action describing two
species and possessing an exact chiral symmetry. This is the minimum number of species required by the well known ``no-go'' theorems.
February 4, 2008
Speaker: Professor Weonjong Lee, Seoul University
Title: Calculating CP violation parameter, B_K using improved staggered fermions
Abstract:
A recent progress in calculating B_K using staggered fermions are reviewed. In particular, there has been a series of progress in understanding the power counting rules through numerical study on pion spectrum in parallel with a theoretical development of staggered chiral perturbation theory. This progress is essential to calculate B_K with extremely high precision.
February 11, 2008
Speaker: Professor Lisa Randall, Harvard University
Title: "GIM in the Bulk"
Abstract:
We show how extra-dimensional theories can naturally explain the flavor
structure of the Standard Model and also how they can shed light on CP
violation.
February 18, 2008
Speaker: Stanley Brodsky, Stanford University and SLAC
Title: "The AdS/CFT Correspondence and Light-Front QCD"
Abstract:
The AdS/CFT correspondence between string theory in AdS space and
conformal field theories in physical space-time leads to an analytic,
semi-classical model for strongly-coupled QCD which has scale
invariance and dimensional counting at short distances and color
confinement at large distances. Although QCD is not conformally
invariant, one can nevertheless use the mathematical representation of
the conformal group in five-dimensional anti-de Sitter space to
construct an analytic approximation to the theory. The AdS/CFT
correspondence also provides a mapping between the fifth-dimensional
coordinate of AdS space and a specific impact variable which measures
the separation of the quark and gluonic constituents within the hadron.
This connection allows one to compute the analytic form of the
frame-independent light-front wavefunctions of mesons and baryons, the
fundamental entities which encode hadron properties and which allow the
computation of exclusive scattering amplitudes. A new integrable
relativistic light-front equation in ordinary space-time is found which
reproduces the results obtained using the fifth-dimensional theory. An
extension for massive quarks will also be discussed. Since they are
complete and orthonormal, the AdS/CFT wavefunctions can also be used as
a basis for the diagonalization of the full light-front QCD
Hamiltonian, thus systematically improving the AdS/CFT approximation.
February 25, 2008
Speaker: Raphael Bousso, University of California - Berkeley
Title: "The measure problem in cosmology"
March 10, 2008
Speaker: Professor Sinya Aoki, Tsukuba University
Title: Nuclear force from lattice QCD
Abstract:
Nucleon-nucleon (NN) potential is studied by lattice QCD simulations in the quenched approximation. An NN potential $V_{\rm NN}(r)$ isdefined from the equal-time Bethe-Salpeter amplitude with alocal interpolating operator for the nucleon. By studying the NN interaction in the $^1$S$_0$ and $^3$S$_1$ channels, we show thatthe central part of $V_{\rm NN}(r)$ has a strong repulsive core of a few hundred MeV at short distances ($r \alt 0.5$ fm) surrounded by anattractive well at medium and long distances.These features are consistent with the known phenomenological features of the nuclear force. More recent progresses are alsodiscussed.
March 24, 2008
Speaker: Patrick Fox, Fermilab National Accelerator Laboratory
Title: "Quark and lepton masses from top loops"
Abstract:
Assuming that the leptons and quarks other than top are massless at
tree level, we show that their masses may be induced by loops involving
the top quark. As a result, the generic features of the fermion mass spectrum arise
from certain combinations of loop factors. Explicitly, we construct a
renormalizable model involving some colored scalar fields, which leads to 1-loop bottom and tau masses, a 2-loop charm mass, 3-loop muon and strange masses, 4-loop masses for up and down quarks,
and a 5-loop electron mass. This realistic pattern of masses does not
require any symmetry to
differentiate the three generations of fermions. The scalar fields may
lead to observable effects in future experiments searching for $\mu \to
e$ conversion in nuclei, lepton-flavor violating kaon decays, and other flavor-changing processes.
April 21, 2008
Speaker: Dr. Yang Bai, Fermilab National Accelerator Laboratory
Title: "Minimal Little Higgs Model and Dark Matter"
Abstract:
We construct a little Higgs model with the most minimal extension of
the standard model gauge group by an extra U(1) gauge symmetry. For
specific charge assignments of scalars, an approximate U(3) global
symmetry appears in the cutoff-squared scalar mass terms generated from
gauge bosons at one-loop level. Hence, the Higgs boson, identified as a
pseudo-Goldstone boson of the broken global symmetry, has its mass
radiatively protected up to scales of 5-10 TeV. In this model, a Z2
symmetry, ensuring the two U(1) gauge groups to be identical, also
makes the extra massive neutral gauge boson stable and a viable dark
matter candidate with a promising prospect of direct detection.
April 28, 2008
Speaker: Prof. Gilad Perez, Stony Brook University
Title: "Top physics at the LHC and warped phenomenology"
Abstract:
We briefly describe the important and intriguing role played by the top within the standard model (SM) of elementary particles. We are thus motivated to improve our (rather poor) knowledge of the top fundamental parameter and couplings. It is very exciting that such a study will be possible, very soon, when the LHC experiment will start running. We demonstrate how the special features of the top quark will allow us to perform precision tests of the SM and open a window to discover beyond the SM physics, focusing on warped extra dimension models as a concrete example.
May 5, 2008
Speaker: Dr. Hooman Davoudiasl, Brookhaven
Title: "The Little Randall-Sundrum Model at the LHC"
Abstract:
We present a predictive warped model of flavor that is cut off at an
ultraviolet scale of order 1000 TeV. This ``Little Randall-Sundrum (LRS)"
model is a volume-truncation, by a factor y~6, of the RS scenario and is
holographically dual to dynamics with number of colors larger by y. The
LRS couplings between Kaluza-Klein states and the Standard Model fields
are explicitly calculable. Assuming separate gauge and flavor dynamics, a
number of unwanted contributions to precision electroweak, Z b b\bar, and
flavor observables are suppressed in the LRS framework, compared with the
RS counterparts. An important consequence of the LRS truncation,
independent of precise details, is a significant enhancement of the clean
(golden) di-lepton LHC signals, by order y^3, due to a larger
``rho-photon" mixing and a smaller inter-composite coupling.
