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Escher-verse
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Hawking's 'Escher-verse' could be theory of everything

Stephen Hawking has come up with a way to describe the universe that suggests it may have the same geometry as mind-boggling images by M. C. Escher.
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RE: Dimensions
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Title: Probing the Concept of Extra Dimensions with Carbon Nanotubes
Authors: Jonas de Woul, Alexander Merle, Tommy Ohlsson

We point out a conceptual analogy between the physics of extra spatial dimensions and the physics of carbon nanotubes which arises for principle reasons, although the corresponding energy scales are at least ten orders of magnitude apart. For low energies, one can apply the Kaluza-Klein description to both types of systems, leading to two completely different but consistent interpretations of the underlying physics. In particular, we discuss in detail the Kaluza-Klein description of armchair and zig-zag carbon nanotubes. Furthermore, we describe how certain experimental results for carbon nanotubes could be re-interpreted in terms of the Kaluza-Klein description. Finally, we present ideas for new measurements that could allow to probe concepts of models with extra spatial dimensions in table-top experiments, providing further links between condensed matter and particle physics.

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Title: Limits on Large Extra Dimensions Based on Observations of Neutron Stars with the Fermi-LAT
Authors: Bijan Berenji, Elliott Bloom, Johann Cohen-Tanugi, for the Fermi-LAT Collaboration

We present limits for the compactification scale in the theory of Large Extra Dimensions (LED) proposed by Arkani-Hamed, Dimopoulos, and Dvali. We use 11 months of data from the Fermi Large Area Telescope (Fermi-LAT) to set gamma ray flux limits for 6 gamma-ray faint neutron stars (NS). To set limits on LED we use the model of Hannestad and Raffelt (HR) that calculates the Kaluza-Klein (KK) graviton production in supernova cores and the large fraction subsequently gravitationally bound around the resulting NS. The predicted decay of the bound KK gravitons to {\gamma}{\gamma} should contribute to the flux from NSs. Considering 2 to 7 extra dimensions of the same size in the context of the HR model, we use Monte Carlo techniques to calculate the expected differential flux of gamma-rays arising from these KK gravitons, including the effects of the age of the NS, graviton orbit, and absorption of gamma-rays in the magnetosphere of the NS. We compare our Monte Carlo-based differential flux to the experimental differential flux using maximum likelihood techniques to obtain our limits on LED. Our limits are more restrictive than past EGRET-based optimistic limits that do not include these important corrections. Additionally, our limits are more stringent than LHC based limits for 3 or fewer LED, and comparable for 4 LED. We conclude that if the effective Planck scale is around a TeV, then for 2 or 3 LED the compactification topology must be more complicated than a torus.

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Public Lecture - Space: The Hunt for Hidden Dimensions



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Posts: 131433
Date:
Extra Dimensions
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Thursday's news that physicists have seen subatomic particles called neutrinos exceed the Universe's speed limit is a picture of science still at work.
The researchers at Cern in Switzerland and Gran Sasso in Italy have tried really hard to find what they might be doing wrong - over three years and thousands of experiments - because they can hardly believe what they are seeing.
The publication of their results is a call for help to pick holes in their methods, and save physics as we now know it.

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RE: Dimensions
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Title: Detecting Vanishing Dimensions via Primordial Gravitational Wave Astronomy
Authors: Jonas Mureika and Dejan Stojkovic
(Version v2)

Lower dimensionality at higher energies has manifold theoretical advantages as recently pointed out by Anchordoqui et al.  Moreover, it appears that experimental evidence may already exist for it: A statistically significant planar alignment of events with energies higher than TeV has been observed in some earlier cosmic ray experiments. We propose a robust and independent test for this new paradigm. Since (2+1)-dimensional spacetimes have no gravitational degrees of freedom, gravity waves cannot be produced in that epoch. This places a universal maximum frequency at which primordial waves can propagate, marked by the transition between dimensions. We show that this cutoff frequency may be accessible to future gravitational wave detectors such as the Laser Interferometer Space Antenna.

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Vanishing dimensions hypothesis
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Did the Early Universe Have One Dimension?

Did the early universe have just one spatial dimension?
That's the mind-boggling concept at the heart of a theory that University at Buffalo physicist Dejan Stojkovic and colleagues proposed in 2010.
They suggested that the early universe -- which exploded from a single point and was very, very small at first -- was one-dimensional (like a straight line) before expanding to include two dimensions (like a plane) and then three (like the world in which we live today).
The theory, if valid, would address important problems in particle physics.
Now, in a new paper in Physical Review Letters, Stojkovic and Loyola Marymount University physicist Jonas Mureika describe a test that could prove or disprove the "vanishing dimensions" hypothesis.

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RE: Dimensions
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Title: Vanishing Dimensions and Planar Events at the LHC
Authors: Luis Anchordoqui, De Chang Dai, Malcolm Fairbairn, Greg Landsberg, Dejan Stojkovic
(Version v2)

We propose that the effective dimensionality of the space we live in depends on the length scale we are probing. As the length scale increases, new dimensions open up. At short scales the space is lower dimensional; at the intermediate scales the space is three-dimensional; and at large scales, the space is effectively higher dimensional. This setup allows for some fundamental problems in cosmology, gravity, and particle physics to be attacked from a new perspective. The proposed framework, among the other things, offers a new approach to the cosmological constant problem and results in striking collider phenomenology and may explain elongated jets observed in cosmic-ray data.

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Title: Shrinking The Braneworld: Black Hole In A Globular Cluster
Authors: Oleg Y. Gnedin, Thomas J. MacCarone, Dimitrios Psaltis, Stephen E. Zepf

Large extra dimensions have been proposed as a possible solution to the hierarchy problem in physics. One of the suggested models, the RS2 braneworldmodel, makes a prediction that black holes evaporate by Hawking radiation on a short timescale that depends on the black hole mass and on the asymptotic radius of curvature of the extra dimensions. Thus the size of the extra dimensions can be constrained by astrophysical observations.
Here we point out that the black hole, recently discovered in a globular cluster in galaxy NGC 4472, places the strongest constraint on the maximum size of the extra dimensions, L less than 0.003 mm. This black hole has the virtues of old age and relatively small mass. The derived upper limit is within an order of magnitude of the absolute limit afforded by astrophysical observations of black holes.

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Nine chapters, two hours of maths, that take you gradually up to the fourth dimension.
Free video download.

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