Physics posts
- February 1, 2011
- 06:37 AM
- 425 views
A wonderful confirmation
by Marco Frasca in The Gauge Connection
Contributions to proceedings to Ghent conference “The many faces of QCD” are starting to appear on arxiv and today appeared one of the most striking one I have heard of at that conference: Orlando Oliveira, Pedro Bicudo and Paulo Silva published their paper (see here). This paper represents a true cornerstone for people doing computations [...]... Read more »
O. Oliveira, P. J. Silva, & P. Bicudo. (2011) What Lattice QCD tell us about the Landau Gauge Infrared Propagators. arxiv. arXiv: 1101.5983v1
FRASCA, M. (2008) Infrared gluon and ghost propagators. Physics Letters B, 670(1), 73-77. DOI: 10.1016/j.physletb.2008.10.022
FRASCA, M. (2009) MAPPING A MASSLESS SCALAR FIELD THEORY ON A YANG–MILLS THEORY: CLASSICAL CASE. Modern Physics Letters A, 24(30), 2425. DOI: 10.1142/S021773230903165X
Marco Frasca. (2008) Infrared behavior of the running coupling in scalar field theory. arxiv. arXiv: 0802.1183v4
- January 29, 2011
- 12:43 AM
- 659 views
Taking flight on light
by gg in Skulls in the Stars
On occasion, a scientific idea comes along that is so simple and elegant that one wonders that it hadn’t been done before! Such is the case with the results of an article published online in Nature Photonics in December, which … Continue reading →... Read more »
Swartzlander, G., Peterson, T., Artusio-Glimpse, A., & Raisanen, A. (2010) Stable optical lift. Nature Photonics, 5(1), 48-51. DOI: 10.1038/NPHOTON.2010.266
- January 28, 2011
- 12:12 PM
- 1,628 views
Dark Matter Reconstruction From Radio Experiments.
by Joseph Smidt in The Eternal Universe
As photons move through the universe they get gravitationally lensed as the pass by large clumps of matter. (As shown in the image above.) Dark matter, being the dominant form of matter, lenses these photons more than anything. Therefore, by studying the lensing properties of incoming photons, in principle we can reconstruct what the profiles of the dark matter doing that lensing.
Now, put (
... Read more »
Michael L. Brown, & Richard A. Battye. (2011) Mapping the dark matter with polarized radio surveys. E-Print. arXiv: 1101.5157v1
- January 28, 2011
- 10:08 AM
- 470 views
The Saga of Landau-Gauge Progators: A Short History
by Marco Frasca in The Gauge Connection
I have never discussed too much in-depth the history of the matter of Yang-Mills propagators in Landau gauge even if I often expressed a clearcut position. This is a kind of disclaimer when I say that I would not like to offend the work of anyone but my results agree excellently well with lattice computations [...]... Read more »
von Smekal, L., Hauck, A., & Alkofer, R. (1997) Infrared Behavior of Gluon and Ghost Propagators in Landau Gauge QCD. Physical Review Letters, 79(19), 3591-3594. DOI: 10.1103/PhysRevLett.79.3591
Aguilar, A., & Natale, A. (2004) A dynamical gluon mass solution in a coupled system of the Schwinger-Dyson equations. Journal of High Energy Physics, 2004(08), 57-57. DOI: 10.1088/1126-6708/2004/08/057
Ph. Boucaud, J. P. Leroy, A. Le Yaouanc, A. Y. Lokhov, J. Micheli, O. Pene, J. Rodriguez-Quintero, & C. Roiesnel. (2005) The Infrared Behaviour of the Pure Yang-Mills Green Functions. arxiv. arXiv: hep-ph/0507104v4
Aguilar, A., Binosi, D., & Papavassiliou, J. (2008) Gluon and ghost propagators in the Landau gauge: Deriving lattice results from Schwinger-Dyson equations. Physical Review D, 78(2). DOI: 10.1103/PhysRevD.78.025010
Cornwall, J. (1982) Dynamical mass generation in continuum quantum chromodynamics. Physical Review D, 26(6), 1453-1478. DOI: 10.1103/PhysRevD.26.1453
Attilio Cucchieri, & Tereza Mendes. (2007) What's up with IR gluon and ghost propagators in Landau gauge? A puzzling answer from huge lattices. PoSLAT2007:297,2007. arXiv: 0710.0412v1
I. L. Bogolubsky, E. -M. Ilgenfritz, M. Müller-Preussker, & A. Sternbeck. (2007) The Landau gauge gluon and ghost propagators in 4D SU(3) gluodynamics in large lattice volumes. PoSLAT2007:290,2007. arXiv: 0710.1968v2
O. Oliveira, P. J. Silva, E. -M. Ilgenfritz, & A. Sternbeck. (2007) The gluon propagator from large asymmetric lattices. PoSLAT2007:323,2007. arXiv: 0710.1424v1
- January 26, 2011
- 06:55 AM
- 686 views
The Saga of Landau-Gauge Propagators
by Marco Frasca in The Gauge Connection
Also today arxiv reserves some interesting papers. But the one that mostly hit my attention is this one by Attilio Cucchieri and Tereza Mendes. Just the title, “The Saga of Landau-Gauge Propagators: Gathering New Ammo”, is a program and I would like to emphasize what is the new ammo: We recently installed at IFSC–USP a [...]... Read more »
Attilio Cucchieri, & Tereza Mendes. (2011) The Saga of Landau-Gauge Propagators: Gathering New Ammo. arxiv. arXiv: 1101.4779v1
- January 25, 2011
- 04:38 PM
- 967 views
This Week in the Universe: January 18th – January 24th
by S.C. Kavassalis in The Language of Bad Physics
Phenomenally beautiful math was the main highlight of this week, I’d say, although none of it for the very faint of heart.
The CMS on SUSY, Bill Unruh on simulated Hawking radiation, Ed Witten on knots, and Schenkel and Van Oystaeyen on noncommutative space(times):
High Energy Physics and Particles:
The LHC Doesn’t Need Data-Collecting Mode To Have Fun
CMS Collaboration (2011). Search for Supersymmetry in pp Collisions at 7 TeV in Events with Jets and Missing Transverse Energy arXiv arXiv: 1101.1628v1
The CMS Collaboration released results this month ruling out supersymmetric particles with masses of less than ~ 0.5 TeV/c2. This is just one of a series of ongoing SUSY related papers analyzing last years data and spitting out constraints on models (which is hugely important). We’ll be seeing results papers for years to come, but it’s nice to see evidence of the LHC being exactly what we all hoped it would be already: the thing that tells us if we’re likely on the right track or not.
For more, see Reality check at the LHC.
General Relativity, Quantum Gravity, et al.:
Measurement of Stimulated Hawking Emission
Silke Weinfurtner, Edmund W. Tedford, Matthew C. J. Penrice, William G. Unruh, & Gregory A. Lawrence (2010). Measurement of stimulated Hawking emission in an analogue system Phys. Rev. Lett., 106 (2), 1302-1306 arXiv: 1008.1911v2
The abstract:
Hawking argued that black holes emit thermal radiation via a quantum spontaneous emission. To address this issue experimentally, we utilize the analogy between the propagation of fields around black holes and surface waves on moving water. By placing a streamlined obstacle into an open channel flow we create a region of high velocity over the obstacle that can include surface wave horizons. Long waves propagating upstream towards this region are blocked and converted into short (deep-water) waves. This is the analogue of the stimulated emission by a white hole (the time inverse of a black hole), and our measurements of the amplitudes of the converted waves demonstrate the thermal nature of the conversion process for this system. Given the close relationship between stimulated and spontaneous emission, our findings attest to the generality of the Hawking process.
Analogues often make me a little uncomfortable in physics, for what are probably obvious reasons, but Bill Unruh has had a lot of success and acceptance with his analogue black hole/white hole models in the past. The line between similar and the same, and if it is actually telling us anything to observe properties in these analogue systems (which have some major fundamental differences) always gets to me in these matters, so I’m going to have to come back to this one to give further comments.
For more, see Wave-Generated ‘White Hole’ Boosts Hawking Radiation Theory: UBC Research.
Ed Witten on Khovanov Homology of Knots.
Edward Witten (2011). Fivebranes and Knots arXiv arXiv: 1101.3216v1
The abstract:
We develop an approach to Khovanov homology of knots via gauge theory (previous physics-based approches involved other descriptions of the relevant spaces of BPS states). The starting point is a system of D3-branes ending on an NS5-brane with a nonzero theta-angle. On the one hand, this system can be related to a Chern-Simons gauge theory on the boundary of the D3-brane worldvolume; on the other hand, it can be studied by standard techniques of S-duality and T-duality. Combining the two approaches leads to a new and manifestly invariant description of the Jones polynomial of knots, and its generalizations, and to a manifestly invariant description of Khovanov homology, in terms of certain elliptic partial differential equations in four and five dimensions.
So Ed Witten is one of those few authors whose work I can feel safe about getting excited over before I’ve read it, and at 146 pages, well, it’s unlikely I’ll ever make it through all of this (although its length is only due to the fact that it very thorough, and thus imaginably very useful). I’m going to defer to the University of Toronto’s Daniel Moskovich from Low Dimensional Topology (which I can’t recommend enough) on this one, as he wrote:... Read more »
CMS Collaboration. (2011) Search for Supersymmetry in pp Collisions at 7 TeV in Events with Jets and Missing Transverse Energy. arXiv. arXiv: 1101.1628v1
Silke Weinfurtner, Edmund W. Tedford, Matthew C. J. Penrice, William G. Unruh, & Gregory A. Lawrence. (2010) Measurement of stimulated Hawking emission in an analogue system. Phys. Rev. Lett., 106(2), 1302-1306. arXiv: 1008.1911v2
Edward Witten. (2011) Fivebranes and Knots. arXiv. arXiv: 1101.3216v1
Alexander Schenkel. (2011) Quantum Field Theory on Curved Noncommutative Spacetimes. arXiv. arXiv: 1101.3492v2
- January 25, 2011
- 03:44 PM
- 595 views
The Tevatron affair and the “fat” gluon
by Marco Frasca in The Gauge Connection
Tevatron is again at the forefront of the blogosphere mostly due to Jester and Lubos. Top quark seems the main suspect to put an end to the domain of the Standard Model in particle physics. Indeed, years and years of confirmations cannot last forever and somewhere some odd behavior must appear. But this is again [...]... Read more »
Frasca, M. (2008) Infrared gluon and ghost propagators. Physics Letters B, 670(1), 73-77. DOI: 10.1016/j.physletb.2008.10.022
Frasca, M. (2009) MAPPING A MASSLESS SCALAR FIELD THEORY ON A YANG–MILLS THEORY: CLASSICAL CASE. Modern Physics Letters A, 24(30), 2425. DOI: 10.1142/S021773230903165X
P. Bicudo, & O. Oliveira. (2010) Gluon Mass in Landau Gauge QCD. arxiv. arXiv: 1010.1975v1
Frasca, M. (2010) Glueball spectrum and hadronic processes in low-energy QCD. Nuclear Physics B - Proceedings Supplements, 196-199. DOI: 10.1016/j.nuclphysbps.2010.10.051
- January 25, 2011
- 01:00 PM
- 1,429 views
What If Dark Energy Were A Phantom Energy?
by Joseph Smidt in The Eternal Universe
Before we get too far ahead of ourselves, let's remember that dark energy being a cosmological constant fits the data very well and has for years. That said, experimental constraints allow for dark energy actually being an exotic form of phantom energy. (So for the time being we have to allow for the possibility and work out the details.) This was recently done by Dabrowski and Denkiewicz.
What
... Read more »
Mariusz P. Dabrowski, & Tomasz Denkiewicz. (2009) Exotic-singularity-driven dark energy. AIP Conference Proceedings. arXiv: 0910.0023v1
- January 24, 2011
- 09:03 AM
- 621 views
Gian Giudice and Lisa Randall in Rome
by Marco Frasca in The Gauge Connection
As usual, also for this year there has been the Festival delle Scienze (Festival of the Sciences) in Rome. This lasted for all the last week and ended this sunday. This is the chance to hear from leading scientists the status of forefront research. This year’s theme was “The End of the World – Instructions [...]... Read more »
Lillie, B., Randall, L., & Wang, L. (2007) The Bulk RS KK-gluon at the LHC. Journal of High Energy Physics, 2007(09), 74-74. DOI: 10.1088/1126-6708/2007/09/074
- January 22, 2011
- 07:56 AM
- 1,702 views
living things and slightly expanding universes
by Greg Fish in weird things
Today, we’re going back to my old frienemy, the arXiv blog. Even though I tend to beat up on it quite a bit, the preprint archive does have some interesting papers, even if the only interesting part about them is shredding them for a skeptical post. Then again, this sort of constant criticism of scientific [...]... Read more »
Hugo Martel, Paul R. Shapiro, & Steven Weinberg. (1997) Likely Values of the Cosmological Constant. Astrophys.J. 492 (1998) 29. arXiv: astro-ph/9701099v1
Don N. Page. (2011) Evidence Against Fine Tuning for Life. n/a. arXiv: 1101.2444v1
- January 21, 2011
- 06:44 AM
- 666 views
CUDA: Lattice QCD on a Personal Computer
by Marco Frasca in The Gauge Connection
At the conference “The many faces of QCD” (see here, here and here) I have had the opportunity to talk with people doing lattice computations at large computer facilities. They said to me that this kind of acitivities imply the use of large computers, user queues (as these resources are generally shared) and months of [...]... Read more »
Nuno Cardoso, & Pedro Bicudo. (2010) Lattice SU(2) on GPU's. arxiv. arXiv: 1010.1486v1
Nuno Cardoso, & Pedro Bicudo. (2010) SU(2) Lattice QCD Simulations on Fermi GPUs. arxiv. arXiv: 1010.4834v1
- January 20, 2011
- 07:25 AM
- 1,353 views
Measuring fields in the tiniest spots
by Joerg Heber in All That Matters
How do you measure a field like electrical or magnetic fields? The field itself is of course not visible. But you can see the effects of a field and use that for the visualization. For example, in case of magnetic fields a nice high school type of experiment is to use iron filings sprayed around a [...]... Read more »
Cang, H., Labno, A., Lu, C., Yin, X., Liu, M., Gladden, C., Liu, Y., & Zhang, X. (2011) Probing the electromagnetic field of a 15-nanometre hotspot by single molecule imaging. Nature, 469(7330), 385-388. DOI: 10.1038/nature09698
- January 20, 2011
- 06:26 AM
- 1,647 views
the amazing disappearing habitable world?
by Greg Fish in weird things
Gliese 581g, we hardly knew you. After a grand announcement, nearly immediate colonization plans from a leading sci-fi blog, and even a tale of supposed alien signals emanating from the newly discovered world, which was actually just an invention of the Daily Mail, rumors started surfacing that this planet wasn’t being detected in subsequent reviews [...]... Read more »
Philip C. Gregory. (2011) Bayesian Re-analysis of the Gliese 581 Exoplanet System. n/a. arXiv: 1101.0800v1
- January 19, 2011
- 01:39 PM
- 758 views
Redefining the Kilogram
by Ryan K in A Quantum of Knowledge
There has been a movement in the physics world for that past few years to standardize the kilogram. At the moment, a kilogram is defined as the mass of the International Prototype Kilogram (IPK), housed at the International Bureau of Weights and Measures (BIPM). The prototype is made of 90% Platinum and 10% Iridium. The [...]... Read more »
Andreas, B., Azuma, Y., Bartl, G., Becker, P., Bettin, H., Borys, M., Busch, I., Gray, M., Fuchs, P., Fujii, K.... (2011) Determination of the Avogadro Constant by Counting the Atoms in a ^{28}Si Crystal. Physical Review Letters, 106(3). DOI: 10.1103/PhysRevLett.106.030801
- January 19, 2011
- 12:14 PM
- 1,115 views
Evidence Against The Universe Being Fine Tuned For Life.
by Joseph Smidt in The Eternal Universe
Many people will tell you that the universe appears fine tuned for life. Don Page has decided to address this issue scientifically by calculating the best value for the cosmological constant needed to support life in the universe and then comparing it to our own. His conclusion is that the cosmological constant is actually an example that our universe is not fine tuned for life.
The
... Read more »
Don N. Page. (2011) Evidence Against Fine Tuning for Life. E-Print. arXiv: 1101.2444v1
- January 18, 2011
- 10:09 AM
- 1,486 views
This Week in the Universe: January 11th – January 17th
by S.C. Kavassalis in The Language of Bad Physics
Astrophysics and Gravitation:
Planck’s Early Results
Planck Collaboration (2011). Planck Early Results: The Planck mission arXiv arXiv: 1101.2022v1
The Early Results Papers from the Planck Collaboration are based on the data acquired by the Planck satellite between August 13th, 2009 to June 6th, 2010. This work is “an overview of the history of Planck in its first year of operations” and was released along side Planck’s Early Release Compact Source Catalogue, “the first data product based on Planck to be released publicly”. Andrew Jaffe has a great summary of the results so far.
For more, see Planck: First results.
Dark Galaxies?
Sukanya Chakrabarti, Frank Bigiel, Philip Chang, & Leo Blitz (2011). Finding Dark Galaxies From Their Tidal Imprints arXiv arXiv: 1101.0815v1
From the abstract:
We describe ongoing work on a new method that allows one to determine the mass and relative position (in galactocentric radius and azimuth) of galactic companions purely from analysis of observed disturbances in gas disks….This approach has broad implications for many areas of astrophysics — for the indirect detection of dark matter (or dark-matter dominated dwarf galaxies), and for galaxy evolution in its use as a decipher for the dynamical impact of satellites on galactic disks. Here, we provide a proof of principle of the method by applying it to infer and quantitatively characterize optically visible galactic companions of local spirals, from the analysis of observed disturbances in outer gas disks.”
The tl;dr version is that they have a technique for detecting companion galaxies that need not be optically visible (which is great, because sometimes we can’t see things for reasons other than them being made out of dark matter) and this paper acts as a proof of concept by using it to correctly infer and characterize galaxies that we already can observe. Does it say anything about having detected a dark matter galaxy? No. If such things existed it could be used to detect them (if they were acting as companion to regular matter galaxies), but it doesn’t say anything about their existence. I genuinely feel I read a different paper than the authors who wrote the below two articles.
For more, see Dark-Matter Galaxy Detected: Hidden Dwarf Lurks Nearby?, The Milky Way might be surrounded by invisible dark matter galaxies.
Not So Standard Standard Candle
This image layout illustrates how NASA's Spitzer Space Telescope was able to show that a "standard candle" used to measure cosmological distances is shrinking -- a finding that affects precise measurements of the age, size and expansion rate of our universe. Image credit: NASA/JPL-Caltech/Iowa State
From the NASA press release:
Astronomers have turned up the first direct proof that “standard candles” used to illuminate the size of the universe, termed Cepheids, shrink in mass, making them not quite as standard as once thought. The findings, made with NASA’s Spitzer Space Telescope, will help astronomers make even more precise measurements of the size, age and expansion rate of our universe.
Obviously, this is rather significant, but the immediate consequence of standard candles not being standard isn’t that it will allow for accurate future measurements of things, it’s that it calls into question the current measurements we have (for things like galactic distances).
From lead author of the study, Massimo Marengo*:
When using Cepheids as standard candles, we must be extra careful because, much like actual candles, they are consumed as they burn.
*He’s also an author on a wonderfully titled paper, Close Binaries with Infrared Excess: Destroyers of Worlds?.
For more, see Cosmology Standard Candle not so Standard After All.
Dynamical Coupled Dark Energy?
Baldi, M., & Pettorino, V. (2011). High-z massive clusters as a test for dynamical coupled dark energy Monthly Notices of the Royal Astronomical Society: Letters DOI: 10.1111/j.1745-3933.2010.00975.x
Abstract:
The recent detection by Jee et al. of the massive cluster XMMU J2235.3−2557 at a redshift z≈ 1.4, with an estimated mass M324= (6.4 ± 1.2) × 1014 M⊙, has been claimed to be a possible challenge to the standard ΛCDM cosmological model. More specifically, the probability to detect such a cluster has been estimated to be ∼0.005 if a ΛCDM model with Gaussian initial conditions is assumed, resulting in a 3σ discrepancy from the standard cosmological model. In this Letter we propose to use high-redshift clusters as the one detected in Jee et al. to compare the cosmological constant scenario with interacting dark energy models. We show that coupled dark energy models, where an interaction is present between dark energy and cold dark matter, can significantly enhance the probability to observe very massive clusters at high redshift.
So I actually haven’t read this paper yet, but was told by a cosmologist frien... Read more »
Planck Collaboration. (2011) Planck Early Results: The Planck mission. arXiv. arXiv: 1101.2022v1
Sukanya Chakrabarti, Frank Bigiel, Philip Chang, & Leo Blitz. (2011) Finding Dark Galaxies From Their Tidal Imprints. arXiv. arXiv: 1101.0815v1
Baldi, M., & Pettorino, V. (2011) High-z massive clusters as a test for dynamical coupled dark energy. Monthly Notices of the Royal Astronomical Society: Letters. DOI: 10.1111/j.1745-3933.2010.00975.x
Turok, N. (2011) Particle physics: Beyond Feynman's diagrams. Nature, 469(7329), 165-166. DOI: 10.1038/469165a
- January 18, 2011
- 09:21 AM
- 663 views
Physics of the Riemann Hypothesis
by Marco Frasca in The Gauge Connection
In this blog I discuss frequently about one of the Clay Institute’s Millenium Prize problems: Mass gap and existence of a quantum Yang-Mills theory. Sometime I also used the Perelman’s theorem containing Poincarè’s conjecture to discuss about some properties of quanum gravity and also Cramer-Rao statistical bound. Today on arxiv I have found a beautiful [...]... Read more »
Daniel Schumayer, & David A. W. Hutchinson. (2011) Physics of the Riemann Hypothesis. arxiv. arXiv: 1101.3116v1
Berry, M., & Keating, J. (1999) The Riemann Zeros and Eigenvalue Asymptotics. SIAM Review, 41(2), 236. DOI: 10.1137/S0036144598347497
- January 16, 2011
- 08:37 AM
- 766 views
What is Science?
by Marco Frasca in The Gauge Connection
Reading this Lubos’ post about a very good site (this one) I entered into the comment area and I have found the following declaration by him: Science is a meritocracy where answers are determined by objective criteria, and for most of the difficult questions, only one or a few people know the right answer and [...]... Read more »
D. Dudal, M. S. Guimaraes, & S. P. Sorella. (2010) Glueball masses from an infrared moment problem and nonperturbative Landau gauge. arxiv. arXiv: 1010.3638v3
- January 14, 2011
- 10:45 AM
- 995 views
Computer-enhanced images with almost perfect resolution
by Joerg Heber in All That Matters
I used to laugh at those TV series and movies where crime investigators could take a surveillance camera photo, however fuzzy and blurred, and enhance its resolution beyond belief to the point where every possible (and impossible) detail becomes visible. I stopped laughing last week at a conference when I became aware of a 2009 [...]... Read more »
Gazit, S., Szameit, A., Eldar, Y., & Segev, M. (2009) Super-resolution and reconstruction of sparse sub-wavelength images. Optics Express, 17(26), 23920. DOI: 10.1364/OE.17.023920
- January 12, 2011
- 12:31 PM
- 1,813 views
First Planck Results: The Sunyaev-Zeldovich Effect.
by Joseph Smidt in The Eternal Universe
There's been many bloggers writing about the first Planck results presented here at AAS and in Europe but I would like to write a little more than has been written on the Sunyeav-Zeldovich results as I think they are impressive. Impressive both in terms of the science we get as well as well as this particular example shows how precise CMB experiments have become. I will focus on the results
... Read more »
The Planck Collaboration. (2011) Planck Early Results: The all-sky Early Sunyaev-Zeldovich cluster sample. Submitted to A. arXiv: 1101.2024v1
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