4,159 research outputs found
Quantization of Space and Time in 3 and in 4 Space-time Dimensions
The fact that in Minkowski space, space and time are both quantized does not
have to be introduced as a new postulate in physics, but can actually be
derived by combining certain features of General Relativity and Quantum
Mechanics. This is demonstrated first in a model where particles behave as
point defects in 2 space dimensions and 1 time, and then in the real world
having 3+1 dimensions. The mechanisms in these two cases are quite different,
but the outcomes are similar: space and time form a (non-cummutative) lattice.
These notes are short since most of the material discussed in these lectures
is based on two earlier papers by the same author (gr-qc/9601014 and
gr-qc/9607022), but the exposition given in the end is new.Comment: Lectures held at the NATO Advanced Study Institute on ``Quantum
Fields and Quantum Space Time", Carg\`ese, July 22 -- August 3, 1996. 16
pages Plain TeX, 6 Figure
Performance of the ATLAS Tau and Missing Energy triggers with 7 TeV proton proton collisions at the LHC
A study of the performance of the ATLAS tau and missing energy triggers with
data collected in spring 2010 at {\surd}s = 7 TeV proton-proton collisions at
the Large Hadron Collider (LHC) is presented. A comparison was performed
between data and Monte Carlo simulations for the tau and missing transverse
energy triggers. As well as a comparison between missing transverse energy
trigger quantities and their offline reconstructed counterparts. Tau trigger
results compare well with predictions from Monte Carlo simulations. Slight
deviations are observed for tau shower shape quantities. Possible sources
contributing to the discrepancy such as the simulation of the underlying event
are currently being studied. The missing transverse energy reconstructed by the
Event Filter is well correlated with the offline result. In addition, there is
good agreement between the results obtained with collision data and Monte Carlo
simulations.Comment: 3 pages, Proceedings for the Hadron Collider Physics Symposium 201
Quantum Gravity as a Dissipative Deterministic System
It is argued that the so-called holographic principle will obstruct attempts
to produce physically realistic models for the unification of general
relativity with quantum mechanics, unless determinism in the latter is
restored. The notion of time in GR is so different from the usual one in
elementary particle physics that we believe that certain versions of hidden
variable theories can -- and must -- be revived. A completely natural procedure
is proposed, in which the dissipation of information plays an essential role.
Unlike earlier attempts, it allows us to use strictly continuous and
differentiable classical field theories as a starting point (although discrete
variables, leading to fermionic degrees of freedom, are also welcome), and we
show how an effective Hilbert space of quantum states naturally emerges when
one attempts to describe the solutions statistically. Our theory removes some
of the mysteries of the holographic principle; apparently non-local features
are to be expected when the quantum degrees of freedom of the world are
projected onto a lower-dimensional black hole horizon. Various examples and
models illustrate the points we wish to make, notably a model showing that
massless, non interacting neutrinos are deterministic.Comment: 20 pages plain TeX, 2 figures PostScript. Added some further
explanations, and the definitions of `beable' and `changeable'. A minor error
correcte
Gedanken Experiments involving Black Holes
Analysis of several gedanken experiments indicates that black hole
complementarity cannot be ruled out on the basis of known physical principles.
Experiments designed by outside observers to disprove the existence of a
quantum-mechanical stretched horizon require knowledge of Planck-scale effects
for their analysis. Observers who fall through the event horizon after sampling
the Hawking radiation cannot discover duplicate information inside the black
hole before hitting the singularity. Experiments by outside observers to detect
baryon number violation will yield significant effects well outside the
stretched horizon.Comment: 22 pages (including 7 figures), SU-ITP-93-1
Discrete Time from Quantum Physics
't Hooft has recently developed a discretisation of (2+1) gravity which has a
multiple-valued Hamiltonian and which therefore admits quantum time evolution
only in discrete steps. In this paper, we describe several models in the
continuum with single-valued equations of motion in classical physics, but with
multiple-valued Hamiltonians. Their time displacements in quantum theory are
therefore obliged to be discrete. Classical models on smooth spatial manifolds
are also constructed with the property that spatial displacements can be
implemented only in discrete steps in quantum theory. All these models show
that quantization can profoundly affect classical topology.Comment: 21 pages with 2 figures, SU-4240-579 (figures corrected in this
version
Colour confinement as dual Meissner effect: gauge theory
We demonstrate that confinement in gauge theory is produced by dual
superconductivity of the vacuum. We show that for (temperature of
deconfining phase transition) the symmetry related to monopole charge
conservation is spontaneously broken; for the symmetry is restored.Comment: 10 pages + 4 figures, uuencoded shell archiv
Vortices versus monopoles in color confinement
We construct the creation operator of a vortex for SU(2) pure gauge theory
using the methods developed for monopoles. We interpret its vacuum expectation
value as a disorder parameter for the deconfinement phase transition and find
that it behaves in the vacuum in a similar way to monopoles. Results are
extrapolated to the thermodynamical limit using finite-size scaling.Comment: Talk presented at Lattice2000 (Topology and Vacuum), 4 page
Black Hole Horizons and Complementarity
We investigate the effect of gravitational back-reaction on the black hole
evaporation process. The standard derivation of Hawking radiation is
re-examined and extended by including gravitational interactions between the
infalling matter and the outgoing radiation. We find that these interactions
lead to substantial effects. In particular, as seen by an outside observer,
they lead to a fast growing uncertainty in the position of the infalling matter
as it approaches the horizon. We argue that this result supports the idea of
black hole complementarity, which states that, in the description of the black
hole system appropriate to outside observers, the region behind the horizon
does not establish itself as a classical region of space-time. We also give a
new formulation of this complementarity principle, which does not make any
specific reference to the location of the black hole horizon.Comment: Some minor modifications in text and the title chang
A semiclassical realization of infrared renormalons
Perturbation series in quantum field theory are generally divergent
asymptotic series which are also typically not Borel resummable in the sense
that the resummed series is ambiguous. The ambiguity is associated with
singularities in the Borel plane on the positive real axis. In quantum
mechanics there are cases in which the ambiguity that arises in perturbation
theory cancels against a similarly ambiguous contribution from
instanton--anti-instanton events. In asymptotically free gauge theories this
mechanism does not suffice because perturbation theory develops ambiguities
associated with singularities in the Borel plane which are closer to the origin
by a factor of about N (the rank of the gauge group) compared to the
singularities realized by instanton events. These are called IR renormalon
poles, and on R**4 they do not possess any known semiclassical realization. By
using continuity on R**3 x S**1, and by generalizing the works of Bogomolny and
Zinn-Justin to QFT, we identify saddle point field configurations, e.g.,
bion--anti-bion events, corresponding to singularities in the Borel plane which
are of order N times closer to the origin than the 4d BPST
instanton--anti-instanton singularity. We conjecture that these are the leading
singularities in the Borel plane and that they are the incarnation of the
elusive renormalons in the weak coupling regime.Comment: 4 page
London Penetration Length and String Tension in SU(2) Lattice Gauge Theory
We study the distribution of the color fields due to a static quark-antiquark
pair in SU(2) lattice gauge theory. We find evidence of dual Meissner effect.
We put out a simple relation between the penetration length and the string
tension.Comment: uuencoded compressed Postscript file (text+figures
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