So my readers probably noticed the fact that this blog just stopped mid-February, without any explanation. Life in our local part of the universe was substantially more chaotic than usual. World wide protests, devastating natural disasters, nuclear fears, war, and us just trying to go about our day to day lives, buying a home, securing funding, getting sick, planning a wedding, all the while not looking at what was sitting just out of the corner of our eyes.
When the world is in crisis, physics doesn’t stop, science doesn’t stop. Wars, famine, the need to rebuild – all of these are actually great motivators for researchers. Unfortunately, most of us aren’t in fields that can actually offer anything close to intellectual assistance during these times. There is a strange and sad fact about this planet and the animals that inhabit it though, and that is that there is always some part of the world that is in crisis. If we took a pause every time something unimaginable to us happened, very little would ever get done. Nevertheless, I paused.
To get back into things, here’s about a months worth of reading – there should be two other posts out later this week (back to some more serious blogging too). Astrophysics and Gravitation gives us some updates on the MOND versus dark matter debate (is MOND winning? or have we already seen dark matter?), a silly paper on stars with wormhole centres, another success for Einstein@Home, a possible explanation for the “Fermi Bubble”, a new value for the Hubble constant, a long overdue fix for the Pioneer Anomaly, and a huge explosion in space for NASA. Lots of news from CERN and Fermilab in High Energy & Particles, including the search for SUSY at the LHC, the hunt for the Higgs, a single top quark at the CMS, heavy antimatter for ALICE, the much hyped results of new physics at the Tevatron, and using a Fermi-Fermi gas to model the Big Bang. Finally in General Relativity & Quantum Gravity we get a lesson on quantum Riemann surfaces in Chern-Simons theory, a curious experiment using gravity waves to suss out dimensionality, an introduction to group field theories, BF models of gravity, and spin foams, an update on the status of Horava gravity, an absurd paper on life inside black holes, and an essay from the 1960s by George Gamow.
Astrophysics and Gravitation:
MOND vs Dark Matter, Again?
MOND is Winning?
Stacy S. McGaugh (2011). A Novel Test of the Modified Newtonian Dynamics with Gas Rich Galaxies Phys.Rev.Lett.106:121303,2011 arXiv: 1102.3913v1
No, it’s not (maybe in the Charlie Sheen sense though). I’ve honestly never been enchanted with dark matter, the fact that it’s this giant unknown bothers me, and MOND holds a lot of appeal, logically for me, but the fact is, it doesn’t work, in the original form or any current one. Yes, some observations do fit into MOND predictions – we wouldn’t be talking about it now if it was entirely unphysical – but MOND is also wrong about a lot of things (you know, like the CMB). Yes, whatever this data was collected on gas rich galaxies probably does fit with what MOND predicts, and may very well disagree with Lambda-CDM (it’s certainly not a perfect model), but if MOND is wrong about other things, it’s still wrong. If someone comes up with a Modified Modified Newtonian dynamics that explains the CMB and fits with the Bullet Cluster, then we’ll talk.
For more, see Gas Rich Galaxies Confirm Prediction of Modified Gravity Theory (PR), Is this the end of dark matter?, Alternate theory poses dark matter challenge, More Evidence Against Dark Matter?, Dark Matter: Just Fine, Thanks,
Has EDELWEISS Seen Dark Matter?
EDELWEISS Collaboration (2011). Final results of the EDELWEISS-II WIMP search using a 4-kg array of cryogenic germanium detectors with interleaved electrodes arXiv arXiv: 1103.4070v2
No, it hasn’t. Well, probably not, anyway. So, the EDELWEISS-II collaboration released some fairly unexciting results, that some people are jumping on as evidence for dark matter. Why? Because the results point to possible evidence for signals for a few WIMP candidates. The CDMS collaboration last year published similarly tentative claims, though the energies of the EDELWEISS and CDMS candidates are different and thus both cannot be the same WIMP (if they are actually anything at all). The noise here is very high, so high that it’s not even clear if any of these are signals at all. People on the project don’t even really believe they’ve seen anything. The spokesman for EDELWEISS, Gilles Gerbier, said, “We cannot say for sure that there is no signal. We are in the uncomfortable situation… We may have a signal but we cannot make any claim now.” So, have we seen dark matter? No, it doesn’t sound like it. It’s not 100% out of the question, however (but probably 99.9% out of it).
“Stars Could Have Wormholes at Their Cores”
V. Dzhunushaliev, V. Folomeev, B. Kleihaus, & J. Kunz (2011). A Star Harbouring a Wormhole at its Center arXiv arXiv: 1102.4454v1
I’m sad I left talking about this article for so long because now it’s old news, but it’s just silly. Hey, let’s create some nonsensey sounding “phantom” matter and then say that wormholes can connect stars because of it! Why? Because speculation is fun! If anyone is taking this seriously, I can write up a “why this isn’t based on anything” post. I don’t call this science, I call it science fiction (but that doesn’t mean we’re not working on teleporters and cloaking devices today).
For more, see Stars Could Have Wormholes at Their Cores, Say Astrophysicists (TechReview arXiv blog), Stellar Wormholes May Exist.
Another Einstein@Home Success
B. Knispel, et al., (2011). Arecibo PALFA Survey and Einstein@Home: Binary Pulsar Discovery by Volunteer Computing The Astrophysical Journal Letters, 732, L1 (2011) arXiv: 1102.5340v2
I love these citizen science accomplishments. The Einstein@Home project has made its second discovery of a radio pulsar orbiting a white dwarf star. The pulsar, J1952+2630, was discovered within data collected back in 2005. J1952+2630′s white-dwarf companion is especially massive, suggesting the pulsar belongs to this rare class of intermediate-mass binary pulsars, making it the 6th of its type known. Congrats, Einstein@Home!
Possible Origin of the Fermi Bubble?
K. S. Cheng, D. O. Chernyshov, V. A. Dogiel, C. -M. Ko, & W. -H. Ip (2011). Origin of the Fermi Bubble arXiv arXiv: 1103.1002v1
Remember that “unknown” gamma ray “bubble” structure discovered last year? A recent paper has suggested that it might be caused by some supermassive black hole “star capture process” at the centre of our galaxy. Honestly, I’ve got no means to judge this one; they claim it’s better than any other explanation, so let’s leave it at that for now.
For more, see Star-hungry black hole could blow galactic ‘bubbles’.
Hubbles Gives a Better Estimate for Speed of Universe’s Expansion
Riess, A., Macri, L., Casertano, S., Lampeitl, H., Ferguson, H., Filippenko, A., Jha, S., Li, W., & Chornock, R. (2011). A 3% SOLUTION: DETERMINATION OF THE HUBBLE CONSTANT WITH THE AND WIDE FIELD CAMERA 3 The Astrophysical Journal, 730 (2) DOI: 10.1088/0004-637X/730/2/119
Hubble’s Wide Field Camera 3 has provided a new and more accurate measurement of the Hubble constant, H0 = 73.8 ± 2.4 (km/s)/Mpc based off of distance and redshift data. In 2010, gravitational lensing data helped put H0 at 72.6 ± 3.1(km/s)/Mpc, while the WMAP seven-year results arrived at H0 = 71.0 ± 2.5 (km/s)/Mpc. So, are we narrowing in on the right value? With those errors, it’s really hard to say. Does this prove anything about the existence of dark energy? No…
For more, see (in order of increasing credulity) Have scientists cracked the speed at which the universe is expanding?, The Universe is expanding at 73.8 +/- 2.4 km/sec/megaparsec! So there., The Hubble telescope eliminates one possible alternative to dark energy, Dark energy is not an illusion after all.
Say Good-Bye to the Pioneer Anomaly?
F. Francisco, O. Bertolami, P. J. S. Gil, & J. Páramos (2011). Modelling the reflective thermal contribution to the acceleration of the Pioneer spacecraft arXiv arXiv: 1103.5222v1
This isn’t one I’ve read thoroughly, but it seems quite plausible. The Pioneer anomaly has never sat well with me, so I might be a little too eager to accept this explanation, but if it just comes down to some uneven heat radiation, I really wouldn’t be very surprised. I’d be happy not to call this an anomaly anymore.
For more, see Pioneer Anomaly Solved By 1970s Computer Graphics Technique (TechReview arXiv Blog). Solved by a 1970s computer graphics technique? No, no it wasn’t, but I won’t necessarily argue with the “solved” part.
NASA Sees Huge Explosion
By their powers combined, NASA’s Swift, Hubble Space Telescope and Chandra X-ray Observatory observed a massive, and beautiful, explosion (now named GRB 110328A) at the centre of a distant galaxy. What was it? The usual party line is “supermassive black hole up to no good”, but with what little we know about the centre of galaxies, it’s not very meaningful to speculate in any particular direction.
High Energy Physics and Particles:
LHC Searches for Supersymmetry
Philip Bechtle, Klaus Desch, Herbi K. Dreiner, Michael Krämer, Ben O’Leary, Carsten Robens, Björn Sarrazin, & Peter Wienemann (2011). What if the LHC does not find supersymmetry in the sqrt(s)=7 TeV run? arXiv arXiv: 1102.4693v1
O. Buchmueller, & et al. (2011). Implications of Initial LHC Searches for Supersymmetry arXiv arXiv: 1102.4585v1
ATLAS Collaboration (2011). Search for Supersymmetry Using Final States with One Lepton, Jets, and Missing Transverse Momentum with the ATLAS Detector in sqrt[s]=7 TeV pp Collisions Physical Review Letters, 106 (13) DOI: 10.1103/PhysRevLett.106.131802
Dine, M., & Mason, J. (2011). Supersymmetry and its dynamical breaking Reports on Progress in Physics, 74 (5) DOI: 10.1088/0034-4885/74/5/056201
Part of me hopes that “SUSY” will be the new “it” baby name for this year, seeing how often everyone is saying it these days. There is practically as much excitement for ruling out (or in) supersymmetry as there is for finding the Higgs. Has the LHC (or anyone else) seen evidence for supersymmetry? No. Should they have yet? No, but it depends on what you were looking for specifically. Like everything HEP, some models have lower energy predictions, some have higher, and experimental physics is all about ruling out segments of those predictions. What if the LHC doesn’t see supersymmetry at all? Okay, some people will move on, some people will push their theories to higher energies. Things like SUSY are almost impossible to rule out entirely because there are so many different versions out there. I realise a statement like that sounds rather unscientific, “Well you can never completely rule out the existence of [blank] because maybe [blank] is more like this instead and you couldn’t see it where you were looking before”, and, wait… Hmm, I wasn’t trying to make an anti-SUSY point when I started this, I actually kind of like SUSY. Let me come back to this. At this stage, all we can say is that the parameter space for SUSY has been further constrained, thanks to ATLAS and the CMS.
For more, see Implications of 35/pb SUSY searches on best fit parameters., Beautiful theory collides with smashing particle data, What if the LHC doesn’t see SUSY?, The Large Hadron Collider enters the race for supersymmetry, Results from the first published search for supersymmetry at ATLAS have arrived.
The LHC Hunts the Higgs
CMS Collaboration (2011). Measurement of WW Production and Search for the Higgs Boson in pp Collisions at sqrt(s) = 7 TeV arXiv arXiv: 1102.5429v2
ATLAS and the CMS have decreased the MSSM Higgs parameter space a little bit more, which is exactly what we’d hoped for. It seems like the LHC might be very close to the Higgs by the end of this year.
Rivalry Drives Higgs Hunt
For more, see First Measurement of W+W− Production and Search for Higgs Boson in pp Collisions at √s=7TeV (pdf, CMS Statement), LHC publishes first Higgs measurements, LHC seriously into Higgs searches.
The CMS Sees a Single Top Quark
Almost surprisingly fast, the LHC has seen evidence of single top quark production, something that took the Tevatron years to build up too (the difference in energy is what really matters here). The ease at which the data was mined for this signal should make people very optimistic that if new physics is in there, it won’t stay buried in bins for too long.
ALICE To Present Results on Record Size Antimatter Observations
CERN’s ALICE collaboration has seen the formation of four anti-nuclei of Helium 4, which are the heaviest kind of antimatter we can currently make in a lab. ALICE is catching up to RHIC quickly in the quest for large anti-nuclei. This is not only an impressive accomplishment, but it can help us understand the early universe better, by creating nuclei that would have existed then.
For more, see ALICE’s wonderland reveals the heaviest antimatter ever observed (CERN Bulletin).
New Physics at the Tevatron?
Starting in March, gossip began coming out of Fermilab that the Tevatron had seen some “new particle” or “new physics”. A sad truth about big projects that lose their funding is that you often get a lot of over-hyped, lacklustre, results getting publicized as the money runs out. In some cases it’s a mad dash to secure more last minute funding (not likely in this case) and in others it’s more of a “you’ll miss me when I’m gone” kind of PR stunt. Given the fact that the Tevatron’s latest efforts in narrowing in on the Higgs mass range yielded no improvement, I’d say that it’s unlikely that new physics, or new particles, will be able to come out of their data. However, all of the hype neglected to mention what this “new physics” was…
And then we got to see the results:
CDF Collaboration, & T. Aaltonen (2011). Invariant Mass Distribution of Jet Pairs Produced in Association with a W boson in ppbar Collisions at sqrt(s) = 1.96 TeV arXiv arXiv: 1104.0699v1
So, it appears the CDF collaboration has seen some particles with a mass distribution that doesn’t quite fit with anything we know or would expect. They don’t have a huge number of these events, so the statistics aren’t great, and there is also some discussion that the energies (mass distributions) haven’t been measured or interpreted correctly, so unfortunately, nothing can be said for certain at this point (although when is that ever the case). There are some good remarks here A hint of something new in “W+dijets” at CDF and Fermilab: CDF “new force” seminar tonight as well as the recorded seminar: Invariant Mass Distribution of Jet Pairs Produced in Association with a W boson in proton-antiproton Collisions at sqrt(s) = 1.96 TeV. It’s really too soon to say much of anything yet on this “possible discovery”. Despite some reports, it’s not evidence for some non-standard Higgs; we don’t even know if the signal is a real one or not yet.
Strongly Interacting Fermi-Fermi Mixture Gives Insight into Big Bang?
Trenkwalder, A., & et al. (2011). Hydrodynamic Expansion of a Strongly Interacting Fermi-Fermi Mixture Physical Review Letters, 106 (11) DOI: 10.1103/PhysRevLett.106.115304
This one was too quantum/condensed matter for me, but is of some interest to cosmologists: an ultracold Fermi-Fermi mixture provides an interesting model for very early universe conditions.
General Relativity, Quantum Gravity, et al.:
Quantum Riemann Surfaces in Chern-Simons Theory
Tudor Dimofte (2011). Quantum Riemann Surfaces in Chern-Simons Theory arXiv arXiv: 1102.4847v1
This is a sizable volume on quantum Riemann surfaces within the Chern-Simons theory and definitely a worthwhile to read for those interested in topological quantum field theory. Dimofte ends up with a state integral model like I’ve never seen before for finding analytical solutions for the holomorphic blocks of Chern-Simons theory. It’s not a light read.
Seeing Vanishing Dimensions with Gravity Waves
Mureika, J., & Stojkovic, D. (2011). Detecting Vanishing Dimensions via Primordial Gravitational Wave Astronomy Physical Review Letters, 106 (10) DOI: 10.1103/PhysRevLett.106.101101
This is a really interesting concept, but a paper I haven’t read especially well yet. The authors are suggesting that we might be able to use gravity waves to determine if, at high energies, our spacetime has a lower dimensionality. The basic idea actually seems pretty brilliant – we know we can’t have gravity waves in a (2+1) spacetime, so if we could find a situation with energies high enough that we should expect dimensional reduction, use something like LISA to look for gravity waves. If we see gravity waves, we must be looking at a (3+1), or higher dimension, spacetime. The basic concept really only hitches on us being able to see gravity waves (which we currently can’t, and may not even theoretically ever be able to) and LISA existing (and LISA has just been cancelled). Hmm… Despite the obvious huge problems, there is something I really like about this concept. This is an idea I think warrants further consideration.
A Field-Theoretic Approach to Spin Foam models in Quantum Gravity
Patrizia Vitale (2011). A field-theoretic approach to Spin Foam models in Quantum Gravity arXiv arXiv: 1103.4172v1
I’ve been seeing more and more work on BF models of gravity lately, so I think it might be time I start looking at them more seriously. This is a nice, and fairly short, introduction to some concepts of Group Field Theory as it relates to BF models.
Some Remarks on the Status of Hořava-Gravity
Matt Visser (2011). Status of Horava gravity: A personal perspective arXiv arXiv: 1103.5587v2
Here is a nice, thoughtful, analysis of some of the current investigations into Horava gravity. I especially like some of his concluding remarks:
Without a deeper understanding of the fundamental framework one is operating in, detailed phenomenological studies (and in particular specific applications to cosmology and astrophysics) are simply premature. Specifically, one needs more than hand-waving “of course it runs to general relativity in the IR” arguments. There may be subtle (or even not so subtle) qualitative deviations from general relativity due to the preferred foliation, and really pinning that issue down would be a good idea before investing more time on detailed applications.
Is there life inside black holes? What? No.
Vyacheslav I. Dokuchaev (2011). Is there life inside black holes? arXiv arXiv: 1103.6140v1
I was confused when someone first sent me this paper because it sounded alarmingly crankish. After reading briefly into it, I was convinced it was especially crankish. Could super advanced civilizations live on some weirdly “spacious” orbits “inside” a black hole? This isn’t science, this is an episode of Stargate SG-1. The language issues (and strange diagrams) make it fairly painful to read, but if pushed, I can go through it thoroughly.