Past Quantum Field Theory Seminar

20 January 2015
David Marsh (Perimeter Institute)

Axions are ubiquitous in string theory compactifications. They are
pseudo goldstone bosons and can be extremely light, contributing to
the dark sector energy density in the present-day universe. The
mass defines a characteristic length scale. For 1e-33 eV<m< 1e-20
eV this length scale is cosmological and axions display novel
effects in observables. The magnitude of these effects is set by
the axion relic density. The axion relic density and initial
perturbations are established in the early universe before, during,
or after inflation (or indeed independently from it). Constraints
on these phenomena can probe physics at or beyond the GUT scale. I
will present multiple probes as constraints of axions: the Planck
temperature power spectrum, the WiggleZ galaxy redshift survey,
Hubble ultra deep field, the epoch of reionisation as measured by
cmb polarisation, cmb b-modes and primordial gravitational waves,
and the density profiles of dwarf spheroidal galaxies. Together

these probe the entire 13 orders of magnitude in axion mass where
axions are distinct from CDM in cosmology, and make non-trivial
statements about inflation and axions in the string landscape. The
observations hint that axions in the range 1e-22 eV<m<1e-20 eV may
play an interesting role in structure formation, and evidence for
this could be found in the future surveys AdvACT (2015), JWST, and
Euclid (>2020). If inflationary B-modes are observed, a wide range
of axion models including the anthropic window QCD axion are
excluded unless the theory of inflation is modified. I will also
comment briefly on direct detection of QCD axions.


  • Quantum Field Theory Seminar
2 December 2014
Boris Zilber

We treat the problem of geometric interpretation of the formalism
of algebraic quantum mechanics as a special case of the general problem of
extending classical 'algebra - geometry' dualities (such as the
Gel'fand-Naimark theorem) to non-commutative setting.  
I will report on some progress in establishing such dualities. In
particular, it leads to a theory of approximate representations of Weyl
in finite dimensional  "Hilbert spaces". Some calculations based on this
theory will be discussed.

  • Quantum Field Theory Seminar
25 November 2014
Guo Chuan Thiang

Topological phases of matter exhibit Bott-like periodicity with respect to
time-reversal, charge conjugation, and spatial dimension. I will explain how
the non-commutative topology in topological phases originates very generally
from symmetry data, and how operator K-theory provides a powerful and
natural framework for studying them.

  • Quantum Field Theory Seminar
28 October 2014
Ricardo Monteiro

We will discuss the relation between perturbative gauge theory and
perturbative gravity, and look at how this relation extends to some exact
classical solutions. First, we will review the double copy prescription that
takes gauge theory amplitudes into gravity amplitudes, which has been
crucial to progress in perturbative studies of supergravity. Then, we will
see how the relation between the two theories can be made manifest when we
restrict to the self-dual sector, in four dimensions. A key role is played
by a kinematic algebraic structure mirroring the colour structure, which can
be extended from the self-dual sector to the full theory, in any number of
dimensions. Finally, we will see how these ideas can be applied also to some
exact classical solutions, namely black holes and plane waves. This leads to
a relation of the type Schwarzschild as (Coulomb charge)^2.

  • Quantum Field Theory Seminar
10 June 2014
John Barrett (Nottingham)
The talk will give a definition of matrix geometries, which are particular types of finite real spectral triple that are useful for approximating manifolds. Examples include fuzzy spheres and also the internal space of the standard model. If time permits, the relation of matrix geometries with 2d state sum models will also be sketched.
  • Quantum Field Theory Seminar