52 research outputs found
Noncommutative Harmonic Analysis, Sampling Theory and the Duflo Map in 2+1 Quantum Gravity
We show that the -product for , group Fourier transform and
effective action arising in [1] in an effective theory for the integer spin
Ponzano-Regge quantum gravity model are compatible with the noncommutative
bicovariant differential calculus, quantum group Fourier transform and
noncommutative scalar field theory previously proposed for 2+1 Euclidean
quantum gravity using quantum group methods in [2]. The two are related by a
classicalisation map which we introduce. We show, however, that noncommutative
spacetime has a richer structure which already sees the half-integer spin
information. We argue that the anomalous extra `time' dimension seen in the
noncommutative geometry should be viewed as the renormalisation group flow
visible in the coarse-graining in going from to . Combining our
methods we develop practical tools for noncommutative harmonic analysis for the
model including radial quantum delta-functions and Gaussians, the Duflo map and
elements of `noncommutative sampling theory'. This allows us to understand the
bandwidth limitation in 2+1 quantum gravity arising from the bounded
momentum and to interpret the Duflo map as noncommutative compression. Our
methods also provide a generalised twist operator for the -product.Comment: 53 pages latex, no figures; extended the intro for this final versio
Emergent non-commutative matter fields from Group Field Theory models of quantum spacetime
We offer a perspective on some recent results obtained in the context of the
group field theory approach to quantum gravity, on top of reviewing them
briefly. These concern a natural mechanism for the emergence of non-commutative
field theories for matter directly from the GFT action, in both 3 and 4
dimensions and in both Riemannian and Lorentzian signatures. As such they
represent an important step, we argue, in bridging the gap between a quantum,
discrete picture of a pre-geometric spacetime and the effective continuum
geometric physics of gravity and matter, using ideas and tools from field
theory and condensed matter analog gravity models, applied directly at the GFT
level.Comment: 13 pages, no figures; uses JPConf style; contribution to the
proceedings of the D.I.C.E. 2008 worksho
Hidden Quantum Gravity in 3d Feynman diagrams
In this work we show that 3d Feynman amplitudes of standard QFT in flat and
homogeneous space can be naturally expressed as expectation values of a
specific topological spin foam model. The main interest of the paper is to set
up a framework which gives a background independent perspective on usual field
theories and can also be applied in higher dimensions. We also show that this
Feynman graph spin foam model, which encodes the geometry of flat space-time,
can be purely expressed in terms of algebraic data associated with the Poincare
group. This spin foam model turns out to be the spin foam quantization of a BF
theory based on the Poincare group, and as such is related to a quantization of
3d gravity in the limit where the Newton constant G_N goes to 0. We investigate
the 4d case in a companion paper where the strategy proposed here leads to
similar results.Comment: 35 pages, 4 figures, some comments adde
Quasitriangular structure and twisting of the 3D bicrossproduct model
We show that the bicrossproduct model...SCOAP
Ponzano-Regge model revisited III: Feynman diagrams and Effective field theory
We study the no gravity limit G_{N}-> 0 of the Ponzano-Regge amplitudes with
massive particles and show that we recover in this limit Feynman graph
amplitudes (with Hadamard propagator) expressed as an abelian spin foam model.
We show how the G_{N} expansion of the Ponzano-Regge amplitudes can be
resummed. This leads to the conclusion that the dynamics of quantum particles
coupled to quantum 3d gravity can be expressed in terms of an effective new non
commutative field theory which respects the principles of doubly special
relativity. We discuss the construction of Lorentzian spin foam models
including Feynman propagatorsComment: 46 pages, the wrong file was first submitte
Gravity induced from quantum spacetime
We show that tensoriality constraints in noncommutative Riemannian geometry
in the 2-dimensional bicrossproduct model quantum spacetime algebra
[x,t]=\lambda x drastically reduce the moduli of possible metrics g up to
normalisation to a single real parameter which we interpret as a time in the
past from which all timelike geodesics emerge and a corresponding time in the
future at which they all converge. Our analysis also implies a reduction of
moduli in n-dimensions and we study the suggested spherically symmetric
classical geometry in n=4 in detail, identifying two 1-parameter subcases where
the Einstein tensor matches that of a perfect fluid for (a) positive pressure,
zero density and (b) negative pressure and positive density with ratio
w_Q=-{1\over 2}. The classical geometry is conformally flat and its geodesics
motivate new coordinates which we extend to the quantum case as a new
description of the quantum spacetime model as a quadratic algebra. The
noncommutative Riemannian geometry is fully solved for and includes the
quantum Levi-Civita connection and a second, nonperturbative, Levi-Civita
connection which blows up as \lambda\to 0. We also propose a `quantum Einstein
tensor' which is identically zero for the main part of the moduli space of
connections (as classically in 2D). However, when the quantum Ricci tensor and
metric are viewed as deformations of their classical counterparts there would
be an O(\lambda^2) correction to the classical Einstein tensor and an
O(\lambda) correction to the classical metric.Comment: 42 pages LATEX, 4 figures; expanded on the physical significanc
Relative Locality in -Poincar\'e
We show that the -Poincar\'e Hopf algebra can be interpreted in the
framework of curved momentum space leading to the relativity of locality
\cite{AFKS}. We study the geometric properties of the momentum space described
by -Poincar\'e, and derive the consequences for particles propagation
and energy-momentum conservation laws in interaction vertices, obtaining for
the first time a coherent and fully workable model of the deformed relativistic
kinematics implied by -Poincar\'e. We describe the action of boost
transformations on multi-particles systems, showing that in order to keep
covariant the composed momenta it is necessary to introduce a dependence of the
rapidity parameter on the particles momenta themselves. Finally, we show that
this particular form of the boost transformations keeps the validity of the
relativity principle, demonstrating the invariance of the equations of motion
under boost transformations.Comment: 24 pages, 4 figures, 1 table. v2 matches accepted CQG versio
Group field theory and simplicial gravity path integrals: A model for Holst-Plebanski gravity
In a recent work, a dual formulation of group field theories as
non-commutative quantum field theories has been proposed, providing an exact
duality between spin foam models and non-commutative simplicial path integrals
for constrained BF theories. In light of this new framework, we define a model
for 4d gravity which includes the Immirzi parameter gamma. It reproduces the
Barrett-Crane amplitudes when gamma goes to infinity, but differs from existing
models otherwise; in particular it does not require any rationality condition
for gamma. We formulate the amplitudes both as BF simplicial path integrals
with explicit non-commutative B variables, and in spin foam form in terms of
Wigner 15j-symbols. Finally, we briefly discuss the correlation between
neighboring simplices, often argued to be a problematic feature, for example,
in the Barrett-Crane model.Comment: 26 pages, 1 figur
3d Spinfoam Quantum Gravity: Matter as a Phase of the Group Field Theory
An effective field theory for matter coupled to three-dimensional quantum
gravity was recently derived in the context of spinfoam models in
hep-th/0512113. In this paper, we show how this relates to group field theories
and generalized matrix models. In the first part, we realize that the effective
field theory can be recasted as a matrix model where couplings between matrices
of different sizes can occur. In a second part, we provide a family of
classical solutions to the three-dimensional group field theory. By studying
perturbations around these solutions, we generate the dynamics of the effective
field theory. We identify a particular case which leads to the action of
hep-th/0512113 for a massive field living in a flat non-commutative space-time.
The most general solutions lead to field theories with non-linear redefinitions
of the momentum which we propose to interpret as living on curved space-times.
We conclude by discussing the possible extension to four-dimensional spinfoam
models.Comment: 17 pages, revtex4, 1 figur
Holonomy observables in Ponzano-Regge type state sum models
We study observables on group elements in the Ponzano-Regge model. We show
that these observables have a natural interpretation in terms of Feynman
diagrams on a sphere and contrast them to the well studied observables on the
spin labels. We elucidate this interpretation by showing how they arise from
the no-gravity limit of the Turaev-Viro model and Chern-Simons theory.Comment: 15 pages, 2 figure
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