Light hadron masses from lattice QCD

Reviews of Modern Physics – April - June 2012 Volume 84, Issue 2

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Zoltan Fodor and Christian Hoelbling

One of the most basic tests of quantum chromodynamics in the strong coupling regime is whether it can successfully predict the spectrum of light hadron masses in terms of a small number of inputs. This article surveys the status of lattice calculations of the spectrum, including the formalism, theoretical uncertainties, and current results. The calculations successfully reproduce relevant parts of the observed spectrum at the percent level.

Published 4 April 2012 (47 pages)

pp. 449-495 [View PDF (1,712 kB)]

So who needs Mach’s Principle for the origin of inertia?

Bearing in mind Basil Hiley’s remark:

To build in wholeness in this preliminary way, we stressed in the UU that the "particle and the field were never separate". Here we were motivated by the work of Frederick Frank at Bristol and Bilby and his co-workers at Sheffield. They had been exploring the geometry of continuous dislocations in crystals and had shown that the equation of migration of dislocation was similar to a relativistic particle dynamics which involved the speed of sound rather than the speed of light. Furthermore the stress forces in the lattice had a similar form to electromagnetic fields. Notice you can't separate the particle from the field: no lattice, no particle implies no field, no particle. We do not give any meaning to the statement that 'the particle is in one of the wave packets'. That is, questions about "empty wave packets" has no meaning in the structure we had in mind.

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Gaussian quantum information

Christian Weedbrook, Stefano Pirandola, Raúl García-Patrón, Nicolas J. Cerf, Timothy C. Ralph, Jeffrey H. Shapiro, and Seth Lloyd

Quantum information processing and communication protocols are typically expressed in terms of discrete units of information, the quantum bits (or qubits). However, certain experimental setups involving, for instance, light or atomic ensembles, are based on continuous quantum system and, in particular, on Gaussian states and operations. This review adapts the main ideas and protocols in the field of quantum information to such systems, and explains their advantages and limitations.

Published 1 May 2012 (49 pages)

pp. 621-669 [View PDF (1,385 kB)]

Glauber states are displaced Gaussians in the phase space of the quantum oscillator normal mode.

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Theoretical aspects of massive gravity

Kurt Hinterbichler

The discovery that the expansion rate of the Universe is accelerating, perhaps due to a nonzero and very small cosmological constant, has led to many speculations regarding modifications to the long distance structure of general relativity. This review discusses modifications which generate a mass for the graviton from a theoretical point of view and includes a treatment of diffeomorphism invariance, interactions, and the low-energy effective field theory treatment of such theories.

Published 7 May 2012 (40 pages)

pp. 671-710 [View PDF (758 kB)]

Dual pairing of symmetry and dynamical groups in physics

D. J. Rowe, M. J. Carvalho, and J. Repka

Symmetries, group theory, and the related theory of Lie algebras underlie quantum mechanics and provide the essential language for the interpretation of physical phenomena. This review discusses foundations and applications of dual representations of pairs of symmetry and dynamical groups primarily in atomic and nuclear physics, especially in the context of bosonic and fermionic many-body systems such as superconductors, molecules, and nuclei. By studying such dual subgroup chains, associations of phenomenological many-body models with microscopic approaches are revealed.

Published 11 May 2012 (47 pages)

pp. 711-757 [View PDF (1,104 kB)]

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Colloquium: Supersolids: What and where are they?

Massimo Boninsegni and Nikolay V. Prokof’ev

Supersolid is the name of an exotic quantum phase of matter, combining the seemingly antithetical properties of crystal and superfluid phases. This phase is expected to exist in rather extreme circumstances, for example, in solid helium near absolute zero. Indeed, claims of its experimental observation have been made. This Colloquium reviews the bulk of the existing phenomenology and offers an interpretation of it, based on theoretical results of first principle computer simulations. Other physical systems in which the supersolid phase might be observed in the laboratory are also described.

Published 11 May 2012 (18 pages)

pp. 759-776 [View PDF (861 kB)]

I predicted super solids before Tony Leggett I think? See my publication list on Wikipedia.

Multiphoton entanglement and interferometry

Jian-Wei Pan, Zeng-Bing Chen, Chao-Yang Lu, Harald Weinfurter, Anton Zeilinger, and Marek Żukowski

Light is made out of photons, which now can be efficiently created, manipulated, and detected. This provides us with the possibility of testing several fundamental aspects of quantum mechanics, ranging from the quantization of energy to the superposition principle, or the violation of Bell inequalities. Also, the degree of control that has been achieved over the properties of the photons has opened up a broad spectrum of applications in the context of quantum information science. This review provides an introduction to multiphoton systems, with an emphasis on their entanglement properties. It also contains an exposition of the fundamental tests that have been carried so far with such systems, as well as the key experiments on quantum communication and computation.

Published 11 May 2012 (62 pages)

pp. 777-838 [View PDF (4,466 kB)]

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How higher-spin gravity surpasses the spin-two barrier

Xavier Bekaert, Nicolas Boulanger, and Per A. Sundell

Gauge theories mediate forces through particle of spin one while the gravitational force is mediated through particles of spin two. It has long been thought that there are no consistent theories with fundamental particles of spin greater than 2, but recent constructions show that while this standard lore is probably true in flat spacetimes, spaces with constant curvature that occur in the presence of a cosmological constant provide a loophole that allows construction of consistent higher-spin generalizations of gravity. This review explains the original no-go results in flat space and then discusses the construction of higher-spin theories in backgrounds with a cosmological constant.

Published 3 July 2012 (23 pages)

pp. 987-1009 [View PDF (453 kB)]

In my gauge theory of gravity, the basic LIF tetrads are compensating spin 1 vector fields from localizing the universal space-time symmetry group for all matter fields. Einstein’s spin 2 gravity would be something analogous to a Cooper pair, i.e. an entangled triplet of a pair of spin 1 quanta with S-state orbital. Of course “graviton" higher spin states with P, D ... orbitals are conceivable. Of course a Cooper pair of spin 1/2 electrons are bound by spin 0 phonons - what binds the gravity tetrads into a pair?

Self interaction? Virtual spin 0 Higgs?