September 21, 2009
Speaker: Prof. Gustavo Burdman, Sao Paulo University
Title: "A Fourth Generation and Electoweak Symmetry Breaking"
We examine the possibility that a heavy fourth generation is responsible for electroweak symmetry breaking, through the condensation of at least one of its quarks. A new interaction strongly coupled to the fourth generation is needed for this to take place. We show that it is possible to model this with one compact warped extra dimension. We discuss the phenomenology of both the quark and lepton sector.
September 28, 2009
Speaker: Manuel Toharia, University of Maryland
Title: "Collider and flavor phenomenology in the scalar sector of Warped Extra Dimensions"
I will review and present new results on the phenomenology of the expected two lightest scalars in the context of warped extra dimensions, the Higgs and the radion. This last one, could be the lightest "new physics" state to be discovered at the LHC in this type of models. Its phenomenology is very similar to the Standard Model (SM) Higgs, with which it can actually mix. When SM fields are allowed to live in the bulk of the extra dimension, new interesting effects appear in the scalar sector of the model. In particular, both the Higgs and the radion can now typically mediate Flavor Changing Neutral Currents at tree level. These will impose bounds on the flavor structure of the model, but also allow for interesting probes in current and future collider experiments.
October 5, 2009
Speaker: Ilia Gogoladze, Bartol Research Institute, University of Delaware
Title: "Yukawa Unification and Sparticle Spectroscopy"
We consider a left-right symmetric SU(4)_c X SU(2)_L X SU(2)_R (4-2-2)
model with gravity mediated supersymmetry breaking. We find that with
4-2-2 compatible non-universal gaugino masses, t-b-\tau Yukawa coupling
unification is consistent with neutralino dark matter abundance and
with constraints from collider experiments. The gluino mass lies close
to that of the lightest neutralino, so that the gluino co-annihilation
channel plays an important role in determining the neutralino relic
abundance. We also explore regions of the parameter space in which the
little hierarchy problem is partially resolved.
October 12, 2009
Speaker: Andrey Katz, University of Marlyland
Title: "More SUSY-breaking vacua in massive SQCD"
Anomalously small gaugino masses are a common feature of various models
of direct gauge mediation. This problem is closely related to the
vacuum structure of the theory. Unfortunately the ISS vacuum in SQCD is
also affected by this problem. Nonetheless massive SQCD can have
SUSY-breaking vacua which are qualitatively different from the ISS
vacuum. In this talk we will focus on these vacua, which are
meta-stable with respect to the ISS vacuum. It will shown that the
gaugino mass problem is properly addressed in these novel vacua. We
will also comment on some properties of these vacua and construct an
example model of gauge mediation.
November 4, 2009
Speaker: Agostino Patella, Swansea University (UK)
Title:"Conformal vs confining scenario in SU(2) with adjoint fermions"
Technicolor is a mechanism for electroweak symmetry breaking,
alternative to the Higgs field. A gauge theory (technicolor sector) is
coupled to the electroweak sector, and electroweak symmetry breaking is
induced by techni-chiral symmetry breaking. While a rescaled version of
QCD was excluded as technicolor model several years ago, theoretical
developments in the last years have shown that gauge theories close to
the conformal window are possible good candidates. SU(2) with two Dirac
fermions in the adjoint representation is one of these candidates.
Understanding whether this theory is confining or IR-conformal is a
challenging problem, which can be addressed by means of numerical
simulations. I will present the most recent spectrum measurements, both
in the mesonic and gluonic sectors close to the chiral limit. I will
discuss some hints of conformal physics, and how the systematic errors
still prevent us from drawing any solid conclusion.
November 16, 2009
Speaker: Mark Hertzberg, MIT
Title: "Approaches to Understanding Inflation: Strings Models and Axions"
Although the observational evidence for cosmological inflation is
growing, the physical mechanism behind it is still unknown. In part
this is because inflation probably occurred at energy scales many
orders of magnitude higher than that at man-made or astrophysical
particle accelerators. So how can we learn about inflation? How does it
constrain microphysical theory? One approach to answering these
questions is primarily theoretical: attempting to embed inflation in
fundamental theories of quantum gravity, such as string theory. Another
approach is primarily observational: looking for signatures left by
light fields that existed during inflation, such as isocurvature
fluctuations from the QCD-axion. In this talk I discuss work on these
November 23, 2009
Speaker: Guido D'Amico, Sissa, Italy
Title: "The Effective Theory of Quintessence and its Observational Signatures"
I will study generic single-field dark energy models, by a
parametrization of the most general theory of their perturbations
around a given background, including higher derivative terms. In
appropriate limits this approach reproduces standard quintessence,
k-essence and ghost condensation. There are no general pathologies
associated to an equation of state w_Q < -1 or in crossing the
phantom divide w_Q = -1. Stability requires that, when w_Q < -1,
dark energy behaves, on cosmological scales, as a fluid with a
virtually zero speed of sound. Theoretical and stability constraints
are summarized on the quintessential plane (1+w_Q) vs. speed of sound
squared. Then I will discuss the effect of dark energy with a zero speed of
sound on non-linear scales. I study the spherical collapse model and
estimate the cluster mass function, finding a distinctive modification
at low redshifts. I will also comment about the effect of clustering
quintessence on cluster measurements.
November 30, 2009
Speaker: Daniel Grin, Caltech
Title: "Cosmological hydrogen recombination: the effect of high-n states and forbidden transitions"
Thanks to the ongoing Planck mission, a new window will be opened on
the properties of the primordial density field, the cosmological
parameters, and the physics of reionization. Much of Planck's new
leverage on these quantities will come from temperature measurements at
small angular scales and from polarization measurements. These both
depend on the details of cosmological hydrogen recombination; use of
the CMB as a probe of energies greater than 1016 GeV compels us to get
the ~eV scale atomic physics right. One question that remains is how high in hydrogen principle quantum
number we have to go to make sufficiently accurate predictions for
Planck. Using sparse matrix methods to beat computational difficulties,
I have modeled the influence of very high (up to and including n=200)
excitation states of atomic hydrogen on the recombination history of
the primordial plasma, resolving all angular momentum sub-states
separately and including, for the first time, the effect of hydrogen
quadrupole transitions. I will review the basic physics, explain the
resulting plasma properties, discuss recombination histories, and close
by discussing the effects on CMB observables.
December 3, 2009
Speaker: Matthew Johnson, Caltech
Title: "Extra dimensions, landscapes of vacua, and runaway domain walls"
Theories that invoke extra dimensions, such as string theory,
typically give rise to many lower-dimensional vacuum states. For
positive energy metastable minima, the cosmological implications of this
picture are dramatic, leading to an eternally inflating universe which
can seed many different vacuum phases through the nucleation of vacuum
bubbles. In this talk, I will describe how domain walls separating
four-dimensional vacua can influence the stability of the overall volume
modulus of a compactification, leading to spacetime solutions containing
either a timelike singularity or a region where space decompactifies,
depending on the metric ansatz. Such solutions can arise in
compactifications of Einstein--Maxwell theory and Type IIB string
theory. The existence of an instability towards decompactification has
important implications for the formation of networks of topological
defects and the population of vacua during eternal inflation.
December 7, 2009
Speaker: Federico Piazza, Perimeter Institute for Theoretical Physics
Title: "Modifying gravity in the Infra Red by imposing an "ultra-strong"
I will give account of a recent attempt to modify the metric-manifold
structure of GR in the infra-red. The proposed modification does not
contain any adjustable parameter as it is effective at length scales
comparable with the inverse curvature. The guiding line for this
modification is a recently proposed "ultra-strong" version of the
equivalence principle, according to which the vacuum expectation value
of the (bare) energy momentum tensor is exactly the same as in flat
space: constant everywhere and quartically divergent with the cut-off.
Such a simple assumption seems to ease some difficulties of the
standard low energy framework for gravity, such as the cosmological
constant problem and the black hole information paradox. I will show
that the proposed modification, when applied to a matter dominated
universe, goes in the direction of a positive acceleration, but it is
too mild to explain the observed amount of acceleration.