Dynamical dimensional reduction and Asymptotic Safety The effective average action approach to Quantum Einstein Gravity (QEG) is discussed as a natural framework for exploring the scale dependent Riemannian geometry and multifractal micro-structure of the effective spacetimes predicted by QEG. Their fractal properties are related to the functional RG flow on theory space, and the special role of the running cosmological constant is emphasized. The prospects of an experimental verification will also be discussed. _____________________________ Vanishing dimension: theory and phenomenology Lower-dimensionality at higher energies has manifold theoretical
advantages as recently pointed out. Moreover, it appears that
experimental evidence may already exists for it - a statistically
significant planar alignment of events with energies higher than TeV has
been observed in some earlier cosmic ray experiments. If this alignment
is not a fluke, then the LHC should be able to see effects associated
with the dimensional crossover. Further, (2+1)-dimensional spacetimes
have no gravitational degrees of freedom, and gravity waves cannot be
produced in that epoch in the early universe. This places a universal
maximum frequency at which primordial gravity waves can propagate, which
may be accessible to future gravitational wave detectors such as LISA.
In this talk, the theoretical motivation for "vanishing dimensions" as
well as generic experimental and observational signature will be
discussed
Modelling continuum dynamics on
discrete space time We will discuss perfect discretizations which aim at mirroring exactly continuum physics on a given lattice. Such discretizations avoid typical artifacts like Lorentz violation, energy dissipation, particle doubling and in particular breaking of diffeomorphism symmetry. Thus the question arises how to distinguish such lattice dynamics from continuum physics.
____________________________ Turning Weyl’s tile argument into
a mathematically rigorous no-go
theorem Weyl's tile argument notes that if space was fundamentally discrete then the set of allowed velocities of a classical particle would not be isotropic. I will generalize Weyl's heuristic argument to a no-go theorem applying to any discrete periodic structure. Since this theorem does not take quantum mechanics into account it should only be regarded as the first step of a program of understanding the phenomenology of discrete spacetimes in a mathematically rigorous way.See arXiv:1109.1963
____________________________ On the Observability of Discrete Spatial
Geometry If quantum geometry is an accurate model of microscopic spatial geometry then two related questions arise, one observational and one theoretical: How and at what scale is the discreteness manifest? And, how is the general relativistic limit achieved? These questions will be discussed in the context of studies of a single atom of geometry. It will be shown that the effective scale of the discreteness could be much larger than the Planck scale. Before this scale can be predicted, the relations between discrete geometry, coherent states, and the semiclassical limit need to be clarified. Work towards this goal, using coherent states in spin foams and the spin geometry theorem of Penrose and Moussouris will be described.
______________________________ Asymptotic safety and minimal length Since asymptotic safety - if true - would make a quantum field theory of gavity consistent "up to arbitrarily high energy", it would seem that this notion is incompatible with the existence of a minimal length. I will argue that this is not necessarily the case, due to ambiguity in the notion of minimal length.
Dark Matter and Dark Energy as a Possible Manifestation of a Fundamental Scale If we take the idea of the Planck length as a fundamental (minimum) scale and if additionally we impose the Cosmological Constant ($Lambda$) as and infrared (IR) cut-off parameter. Then it is possible to demonstrate that Dark Matter effects can emerge as a consequence of an IR-UV mix effect. This opens the possibility of unifying the Dark Energy and Dark matter effects in a single approach.
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Geometric Operators in Loop Quantum Gravity with a Cosmological Constant Loop quantum gravity is a candidate to describe the quantum
gravity regime with zero cosmological constant. One of its key results
is that geometric operators such as area angle volume are quantized. Not
much is known when the cosmological constant is not zero. It is usually
believed that to introduce this parameter in the game we need to use
quantum groups. However due to the complicated algebraic structure
inherent to quantum groups the geometric operators are not yet properly
defined (except the area operator). I will discuss how the use of tensor
operators can circumvent the difficulties and allow to construct a
natural set of observables. In particular I will construct the natural
geometric observables such as angle or volume and discuss some of their
implications.
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Interplay Between Cosmological Constant and DSR Scale I offer brief remarks on several ways in which the cosmological
constant could provide a clue toward quantum gravity. I then focus on
how DSR-relativistic theories can be made compatible with spacetime
expansion (possibly cosmological-constant-governed spacetime expansion),
and how this interplay could manifest itself in data.
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Quantum Gravity RG Flow: A Cosmological Limit Cycle I will discuss evidence for the existence of a limit cycle in the
renormalization group for quantum gravity which is visible in a
minisuperspace approximation. The emergence of the limit cycle can be
studied through a tuning parameter representing the number of dimensions
in which fluctuations of the conformal factor are suppressed. At the
critical value of the tuning parameter all RG trajectories reaching the
UV fixed point have an extended semiclassical regime with a small
positive cosmological constant providing a possible model for a viable
cosmology without fine-tuning.
Quantum-gravity effects as noise for
gravity-wave detectors I discuss a mechanism that can allow Planck scale effects to manifest themselves as a source of lof-frequency noise for interferometers. The mechanism requires a discrete formulation of dynamics at the Planck scale. ____________________ Dancing in the Dark: Images of Quantum Black Holes There have recently been a number of rather surprising suggestions
that the quantum nature of black holes is manifested on macroscopic
scales. This raises the question of just what the image of such an
object should look like. The answer is more than simply academic; with
the advent of the Event Horizon Telescope (EHT), a millimetre-wave very
long baseline array, it is now possible to probe a handful of
supermassive black holes with angular resolutions sufficient to image
their horizons. I will discuss what we might expect to see, and how in
the near future we will begin to empirically probe the existence of
black hole quantum states with horizon scale curvature deviations from
general relativity. _____________________ The Irritating Persistence of Horizons In some approaches to quantum gravity Lorentz invariance is
modified. Without Lorentz invariance one can theoretically see behind
the usual Killing horizon of a black hole if, for example, one allowed
for superluminal propagation. This in turn raises the possibility that
one could in principle probe the singularity and the quantum gravity
regime. We discuss how Lorentz violating black hole solutions in
Einstein-aether theory unfortunately possess another causal boundary
behind the Killing horizon that is impenetrable to any superluminal
mode. We also detail progress in determining the laws of black hole
mechanics and the radiation spectrum from these so-called "universal
horizons". Our results suggest that even if superluminal dispersion at
high frequencies did exist in nature, singularities and their associated
quantum gravity resolutions may very well remain locked behind
horizons.
I will discuss the central role of correlations in
thermodynamic directionality, how strong correlations can distort the
thermodynamic arrow and contrast these distortions in both the classical and
quantum regimes. These distortions constitute non-linear entanglement witnesses,
and give rise to a rich information-theoretic structure. I shall explain how
these results are then cast into the language of fluctuation theorems to derive
a generalized exchange fluctuation theorem, and discuss the limitations of such
a framework.
The IceCube Neutrino Observatory is a cubic-kilometer-scale neutrino detector built into the ice sheet at the geographic South Pole. Completed in December 2010, the detector consists of an array of photomultiplier tubes deployed along 86 cables ("strings") at depths of 1450 to 2450 m, as well as the IceTop air shower array of surface Cherenkov tanks. IceCube is detecting atmospheric neutrinos of energies above approximately 100 GeV at a rate of ~6 per hour, and is currently searching for extraterrestrial neutrinos from cosmic ray accelerators. A measurement of the atmospheric neutrino spectrum can be used to search for possible phenomenological signatures of quantum gravity (QG), such as violations of Lorentz invariance or quantum decoherence, and I present limits we have set on these phenomena in the neutrino sector. To extend the search for QG to much higher energies and cosmological baselines, we require an extraterrestrial neutrino source. In this context, I report on the status of our searches for neutrinos from gamma-ray bursts and from cosmic-ray interactions with the microwave background ("cosmogenic" neutrinos).
String-like objects arise in many quantum field theories.
Well known examples include flux tubes in QCD and cosmic strings. To a first approximation,
their dynamics is governed by the Nambu-Goto action, but for QCD flux tubes
numerical calculations of the energy levels of these objects have become so
accurate that a systematic understanding of corrections to this simple
description is desirable.
In the first part of my talk, I discuss an effective
field theory describing long relativistic strings. The construction parallels
that of the chiral Lagrangian in that it is based on the pattern of symmetry
breaking. To compare with previous works, I will present the results of the
calculation of the S-matrix describing the scattering of excitations on the
string worldsheet.
In the second part of my talk, I will discuss critical
strings from the same point of view and show that the worldsheet S-matrix in
this case is non-trivial but can be calculated exactly. I will show that it
encodes the familiar square-root formula for the energy levels of the string,
the Hagedorn behavior of strings, and argue that the theory on the string
worldsheet behaves like a 1+1 dimensional theory of quantum gravity rather than
a field theory.
If time permits, I will return to the task of computing
the energy levels of flux-tubes using lessons learned from the second part of
my talk.
We present new results on the performance of jet substructure techniques
and their use in distinguishing the signatures of new boosted massive particles
from the QCD background. Advanced approaches to jet reconstruction using jet
grooming algorithms such as filtering, trimming, and pruning are compared.
Measurements of the jet invariant mass for each jet algorithm are compared both
at the particle level to multiple Monte Carlo event generators and at the
detector level for several configurations of the jet grooming algorithms.
The performance of these strategies and improvements in search
sensitivity for new boosted hadronic particles are compared. Recent results
using these techniques for both boosted RPV gluinos and top quark pairs from
new particles are presented. The result is a comprehensive foundation for the
use of substructure algorithms in the search for new physics at the LHC