Tentative Schedule
September 13, 2010
Speaker: Fabian Schmidt, Caltech
Title: "Clustering and velocities of dark matter halos as probes of primordial non-Gaussianity"
Abstract:
Deviations from Gaussianity of the initial seed perturbations offer an
interesting window on the very early Universe. Interestingly,
large-scale structure, in particular the clustering of dark matter halos
and their tracers such as galaxies, promises to be one of the most
sensitive probes of this primordial non-Gaussianity. I will discuss
different approaches to deriving the effect on halo clustering for
general quadratic non-Gaussianity, in particular local biasing and the
peak-background split, which make different sets of assumptions, and
then show that, under certain conditions, they are equivalent in the
large-scale limit. I will also discuss the previously neglected effect
of non-Gaussianity on the velocities of halos, which are observable for
example through redshift distortions.
September 27, 2010
Speaker: Zhenyu Han, Harvard University
Title: "Optimizing the Identification of Boosted W Bosons"
Abstract:
High energy W bosons appear in many new physics processes to
be probed at the LHC. When highly boosted, a hadronically decaying W
boson behaves as a single jet in a collider detector. In this talk, I
discuss how to use jet sub-structure to distinguish it from a high PT
QCD jet. A set of variables are identified and utilized to achieve
significant improvement over previous methods.
October 4, 2010
Speaker: Sergei Dubovsky, New York University
Title: "Exploring the String Axiverse with Astrophysical Black Holes"
Abstract:
Recent advances in X-ray astronomy open the possibility for high
precision spin and mass determination for astrophysical black holes
starting the era of precision black hole physics. These observations
turn astrophysical black holes into sensitive probes of ultra-light
axion-like particles motivated by the strong CP problem and string
theory (the ``Axiverse"). When the axion Compton wavelength matches the
black hole size, the axions develop superradiant atomic bound states
around the black hole "nucleus" through the Penrose superradiance
process. Their occupation number grows exponentially by extracting
rotational energy from the ergosphere, culminating in a rotating
Bose-Einstein axion condensate emitting gravitational waves. This
transfer of angular momentum from the black hole to the axion condensate
results in mass gaps in the spectrum of rapidly rotating black holes,
gives rise to distinctive gravity wave signals, and modifies the near
horizon metric. In particular, the QCD axion with a decay constant of
order of the Grand Unification scale affects the dynamics of stellar
mass black holes. This opens the possibility for the discovery of the
QCD axion through ongoing measurements of black hole spins. The
corresponding gravity wave signal may be within reach of Advanced LIGO. Axions coupled to hidden gauge sectors---hidden valleys---may trigger
the avalanche instability in these sectors in the presence of a black
hole. Electromagnetic echoes of hidden valley avalanches would be
observed as an exotic class of gamma ray bursts.
October 18, 2010
Speaker: Diego Blas, École polytechnique fédérale de Lausanne EPFL
Title: "Non-relativistic Quantum Gravity"
Abstract:
I will review the recent proposal to make general relativity
renormalizable in 4D at the expense of breaking Lorentz invariance.
After introducing the original idea by P. Horava through a toy model, I
will present the realization for the gravitational field where an extra
degree of freedom with respect to general relativity will appear.
Depending on the behavior of the extra mode, the theory may become
unstable or strongly coupled. I will finally show that, despite of this,
one can construct a phenomenologically viable theory free from these
blatant problems.
October 25, 2010
Speaker: Mustafa Amin, MIT
Title: "Lumps and bumps in the early universe"
Abstract:
I will discuss the emergence of large, localized, pseudo-stable
configurations (oscillons) from inflaton fragmentation at the end of
inflation. Remarkably, the emergent oscillons take up >50 per cent of
the energy density of the inflaton. First, I will give an overview of
oscillons, provide some analytic solutions and discuss their stability.
Then, I will discuss the conditions necessary for their emergence and
provide estimates for their cosmological number density. I will show
results from detailed 3+1-dimensional numerical simulations and compare
them to the analytic estimates. Finally, I discuss possible
observational consequences of oscillons in the early universe.
November 5, 2010
Speaker: Christine Davies, Glasgow University
Title: "High precision hadron physics from lattice QCD"
Abstract:
I will describe recent progress in lattice QCD calculations, particularly in the area of charm and bottom physics. This
has led to 1-2% accurate determinations of the parameters of QCD, the quark masses and the strong coupling constant. Lattice
QCD calculations needed for the determination of CKM elements are not as accurate yet, but I will discuss progress on
and future prospects for these.
* Special Theory seminar held at 2:10 pm in 831 Pupin Hall *
November 8, 2010
Speaker: Simon Catterall, Syracuse University
Title: "N=4 Super Yang-Mills on the Lattice"
Abstract:
I will describe a new lattice formulation of N=4 SYM which has the merit of preserving one exact supersymmetryfor non-zero lattice spacing. This exact supersymmetry ensures that the effective action of the lattice theory vanishes to all orders in the coupling constant and that the only counter terms needed in the lattice theory correspond to
renormalizations of the existing terms in the lattice action. We evaluate these renormalization effects at 1-loop. The theorycan be studied at strong coupling using the same Monte Carlo techniques used in lattice QCD. Applications to exploring gauge-gravityduality are described.
November 15, 2010
Speaker: Albion Lawrence, Brandeis University
Title: "Effective field theory analysis of axion monodromy inflation"
Abstract:
We develop a four-dimensional model of "axion monodromy inflation", in
which an axion with sub-Planckian decay constant can wind many times,
eventually travelling super-Placnkian distances, drawing energy from a
four-form field strength. We analyze potential corrections to this
model from the standpoint of 4d effective field theory, and show how it
evades the typical problems with realizing chaotic inflation with
super-Planckian field ranges. We discuss the constraints on this
scenario arising from the coupling to light states such as moduli.
(Based on work in progress with Nemanja Kaloper and Lorenzo Sorbo).
November 19, 2010
Speaker: Alex Prygarin, University of Hamburg, Germany
Title: "BFKL approach and MHV amplitudes"
Abstract:
The main objective of the talk is the application of the Balitsky-Fadin-Kuraev-Lipatov (BFKL) approach to the study of the
maximally helicity violating scattering amplitudes in the Regge limit.
The all-loop ansatz for multi-leg MHV amplitudes proposed by Bern, Dixon and Smirnov (BDS) is violated at two loops for six-gluon
amplitude due to the presence of the Mandelstam (Regge) cuts, which
are described in Yang-Mills theories by the BFKL equation. The BDS violating term in the multi-Regge kinematics was calculated by
Bartels, Lipatov and Sabio Vera (BLS) using the solution to the octet BFKL equation. The BDS ansatz differs from the full MHV amplitude by a
multiplicative function, called the remainder function. The remainder
function for six-point MHV amplitude at two loops was calculated from null polygonal Wilson Loops by Drummond, Henn, Korchemsky and
Sokatchev, then it was expressed in terms of the Goncharov polylogarithms by Del Duca, Duhr and Smirnov and finally greatly
simplified by Goncharov, Spradlin, Vergu and Volovich (GSVV). We analyze the GSVV expression and perform an analytic continuation to
the region where the BDS violating term was found by Bartels, Lipatov and Sabio Vera. The GSVV expression after the analytic continuation
reproduces the BLS result and is in agreement with general properties
of the scattering amplitudes. Using the GSVV formula we obtain the next-to-leading impact factor one needs in the BFKL approach. We also
calculate the three loop leading logarithmic contribution to the remainder function of the six-gluon MHV amplitude. The final part of
the talk is devoted to the interplay of the Regge and collinear limits
in the context of the recent paper of Alday, Gaiotto, Maldacena, Sever and Vieira on the Operator Product Expansion for polygonal null Wilson
Loops.
* Special Theory seminar held at 2:10 pm in 705 Pupin Hall *
November 22, 2010
Speaker: Rachel Rosen, Stockholms universitet
Title: "Phase Transitions of Charged Scalars and White Dwarf Stars"
Abstract:
Recent works have argued that the cores of certain white dwarf stars may
contain a new kind of quantum liquid -- a condensate of charged spin-0
particles. In this talk I will present a field-theoretic approach to
studying the properties of this state of matter at finite temperature
and the phase transition into this state. I will discuss evidence that
the phase transition in white dwarf stars can be first order.
December 6, 2010
Speaker: Tsz Yan Lam, IPMU, Japan
Title: "Primoridal non-Gaussianity and large-scale structure"
Abstract:
Cosmological probes of primordial non-Gaussianity
have recently attracted much attention due to its ability to
discriminate between different inflationary models. In this talk I will
present the signatures of primordial non-Gaussianity on large-scale structure. I will first describe its effect on the distribution of the underlying dark matter field. I will then show how to generalize Doroshkevich's celebrated formulae for the eigenvalues of the initial shear field associated with Gaussian statistics to the local non-Gaussian f_{nl} model. Next I will discuss how to extend the excursion set approach to compute the halo mass function when the primordial perturbation
is non-Gaussian. Finally I will talk about how the pairwise velocity
will be affected. The results will then compare with measurements from N-body simulations.
