So I woke up this morning to several emails about a strange “Higgs sighting” at ATLAS. On a Woit’s blog, a commenter named Higgs? shared an abstract purporting observations of some 115 GeV resonance at CERN. It claims to be from an “internal note” from the ATLAS Collaboration.

Higgs? says:Internal Note

Report number ATL-COM-PHYS-2011-415

Title Observation of a γγ resonance at a mass in the vicinity of 115 GeV/c2 at ATLAS and its Higgs interpretation

Author(s)Fang, Y (-) ; Flores Castillo, L R (-) ; Wang, H (-) ; Wu, S L (University of Wisconsin-Madison)

Imprint 21 Apr 2011. – mult. p.

Subject category Detectors and Experimental Techniques

Accelerator/Facility, Experiment CERN LHC ; ATLAS

Free keywords Diphoton ; Resonance ; EWEAK ; HIGGS ; SUSY ; EXOTICS ; EGAMMA

AbstractMotivated by the result of the Higgs boson candidates at LEP with a mass of about 115~GeV/c2, the observation given in ATLAS note ATL-COM-PHYS-2010-935 (November 18, 2010) and the publication “Production of isolated Higgs particle at the Large Hadron Collider Physics” (Letters B 683 2010 354-357), we studied the γγ invariant mass distribution over the range of 80 to 150 GeV/c2. With 37.5~pb−1 data from 2010 and 26.0~pb−1 from 2011, we observe a γγ resonance around 115~GeV/c2 with a significance of 4σ. The event rate for this resonance is about thirty times larger than the expectation from Higgs to γγ in the standard model. This channel H→γγ is of great importance because the presence of new heavy particles can enhance strongly both the Higgs production cross section and the decay branching ratio. This large enhancement over the standard model rate implies that the present result is the first definitive observation of physics beyond the standard model. Exciting new physics, including new particles, may be expected to be found in the very near future.

Is this a Higgs sighting? Well, the abstract says, “the event rate…is about thirty times larger than the expectation from Higgs to γγ in the standard model” making it certainly not evidence for a Standard Model Higgs. Is it a real observation? That’s a better question at this point. Better still, is this a real note?

I don’t work with CERN, so my login doesn’t give me permission to access internal memos (in fact, I can only read the partial title “Observation of a γγ resonance at a mass”?) although others have told me that the *paper* is actually there and does claim what the abstract is presenting (although perhaps not convincingly).

One of my favourite ATLAS postdocs, Mark Tibbetts, said,

The line from the management is “This is not an official result of the ATLAS experiment.”

“Not an official result”. Hmm…

Now, the authors are a little interesting because they include Sau Lau Wu. Wu is often associated with her excitement, near the end of the LEP days, when her team thought they had observed a Higgs candidate around 114GeV/c^{2} (it was basically ruled out later). The energies being so similar here make this curious.

Another important thing to point out is that the CDF has also been focused on the H→γγ search and has seen no 115 GeV bump in their data [see Search for a Standard Model Higgs Boson Decaying Into Photons at CDF Using 7.0 fb^{-1} of Data [pdf] from April 18th, 2011]. If this sizable 115 GeV bump was being found in ATLAS data, the CDF should also have seen a hint of it, not, nothing.

At this point, I see no reason in speculating on what this [result] means. It’s a rumour. The analysis may be very limited. The data may be non-existent. And it’s not impossible that someone uploaded it to the CERN servers as a joke. If the ATLAS Collaboration were to release it themselves, then we could be excited (and if people want to start throwing around “fourth generation”, “non-Standard Higgs”, “SUSY confirmed/ruled out”, *then *it *might *be reasonable). Until there is an official statement from the collaboration, or even one of the co-authors, this is just gossip. Don’t get excited. Seriously.

For more remarks, analysis, and speculation:

- Not Even Wrong: This Week’s Rumor
- The Reference Frame: ATLAS memo: 4-sigma diphoton bump at LEP’s 115 GeV
- A Quantum Diaries Survivor: Did ATLAS Just See the Higgs
- Résonaances: Higgs in ATLAS, maybe

**Update**: April 25th, 2011: “Spokeswoman quashes Higgs particle rumor” in Nature.

]]>ATLAS’ spokeswoman Fabiola Gianotti stops short of disowning the leaked document, but tells

Naturesignals of the kind reported in the memo show up quite frequently in the course of data analysis and are later falsified after more detailed scrutiny. “Only official ATLAS results, i.e. results that have undergone all the necessary scientific checks by the Collaboration, should be taken seriously,” she says.

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.

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).

For more, see Have Physicists Already Glimpsed Particles of Dark Matter?, Dark matter signal sparks interest, but falls short of discovery.

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.

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!

For more, see Volunteers find another prize pulsar, Einstein@Home Discovers New Binary Radio Pulsar.

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’.

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, *H*_{0} = 73.8 ± 2.4 (km/s)/Mpc based off of distance and redshift data. In 2010, gravitational lensing data helped put *H*_{0} at 72.6 ± 3.1(km/s)/Mpc, while the WMAP seven-year results arrived at *H*_{0} = 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.

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*.

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.

For more, see Star-Eating Black Hole May Be Producing Universe’s Biggest Blast, NASA Telescopes Join Forces to Observe Unprecedented Explosion (PR).

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.

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

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.

For more, see Speedy single top sighting at the LHC, Standard Model Measurements: CMS Collaboration, March 14th, 2011 [pdf].

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).

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…

For more, see the hype: Interesting effect at the Tevatron hints at new physics, At Particle Lab, a Tantalizing Glimpse Has Physicists Holding Their Breaths.

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.

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.

For more, see An Icy Gaze into the Big Bang, Model offers icy gaze into the Big Bang.

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.

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.

For more, see Testing for Vanishing Dimensions, Physicists investigate lower dimensions of the universe.

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.

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.

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.

Joseph Silk (2011). Feedback in Galaxy Formation arXiv arXiv: 1102.0283v1

Abstract:

I review the outstanding problems in galaxy formation theory, and the role of feedback in resolving them. I address the efficiency of star formation, the galactic star formation rate, and the roles of supernovae and supermassive black holes.

Silk’s Figure 1. “The theoretical mass function of galaxies compared to the observed luminosity function.”

So, as most of us know, there are still quite a few puzzles when it comes to how galaxies form. Joseph Silk has put together a little discussion on some of these problems, and, perhaps more interestingly, ways in which they can be rectified (or already have been). For example, cold dark matter simulations alone predicted more *halo* dwarf galaxies than were observed (called the “missing satellites” problem; see Kravtsov and pdf slides). Through both a better understanding of observation (there were in fact more dwarfs out there than we though, they were just very faint) and more sophisticated models (taking into account baryonic physics too), this problem doesn’t seem so huge anymore (it’s not 100% resolved, mind you). There are many other much *less resolved* issues when it comes to gravitation and galaxy formation that are also deserving of some serious study.

Alexandre Amblard, & et al. (2011). Sub-millimetre galaxies reside in dark matter halos with masses greater than 3×10^11 solar masses Nature arXiv: 1101.1080v1

From the press release:

ESA’s Herschel space observatory has discovered a population of dust-enshrouded galaxies that do not need as much dark matter as previously thought to collect gas and burst into star formation.

This is certainly good news for some galaxy formation theorists and another fun piece of the puzzle to think about. The latest analysis of Herschel observations suggest the existence of galaxies that are roughly 300 billion solar masses but with as many stars as expected from a galaxy of *5000* billion solar masses (ie. *that’s not got much dark matter in it*). This is quite fascinating, because most of the current theories dealing with galaxy formation require these huge amounts of dark matter to allow budding galaxies to stay together, but now there are observations that suggest otherwise. It looks like we’ll have to adjust our ideas of dark matter’s role in the galaxy (not that this should surprise anyone).

Earlier this month, there was a really excellent guest post at Cosmic Variance about the state of dark matter detection experiments by Neal Weiner (to complete the discussion of dark matter in the galaxy) so you should give that a read.

San-Jose, P., González, J., & Guinea, F. (2011). Electron-Induced Rippling in Graphene Physical Review Letters, 106 (4) DOI: 10.1103/PhysRevLett.106.045502

So this was a hot topic this month that I’m just getting around to: graphene as an analogy for the Higgs field. Now, as always with these analogy papers, I get a little nervous. When there isn’t an explicit (AdS/CFT-esque) correspondence, it’s really very difficult (and a somewhat philosophical matter) to say what we are actually able to learn from analogies. In this case, the analogy comes from the fact that the “energy landscape” of graphene moving in 2-dimensions is *similar *to that of the Higgs field in 3-dimensions, in that they are both described by a *similar *Mexican hat potential. Okay. There are other situations where we see Mexican hat potentials, like when rotating a bead on a circle, but that doesn’t mean that they would be at all useful in thinking about spontaneous symmetry breaking. Since I don’t really know anything relevant about graphene, quantum criticality, or… well, materials in general, I am completely unqualified to to judge this analogy, but it is still an analogy, not a correspondence. *Similar *and *the same *are, importantly, and fundamentally different.* *

For more, see Theorists turn to graphene for clues to Higgs.

Lloyd, S., Maccone, L., Garcia-Patron, R., Giovannetti, V., Shikano, Y., Pirandola, S., Rozema, L., Darabi, A., Soudagar, Y., Shalm, L., & Steinberg, A. (2011). Closed Timelike Curves via Postselection: Theory and Experimental Test of Consistency Physical Review Letters, 106 (4) DOI: 10.1103/PhysRevLett.106.040403

So this paper was very “win, lose, win” for me. “Closed timelike curves” (CTCs) mean general relativity, which means I’m happy. “Postselection” means quantum interpretations, which means I’m less happy. Now, this isn’t me saying that I don’t think interpretations are wonderful, in fact, they’re my favourite part of quantum mechanics, but it is a huge field, which takes a paper on time travel, away from general relativity, and thus outside of my wheelhouse.

As we know, CTCs are not forbidden by general relativity, although they are usually excluded because of the “logical” paradoxes they lead to (*if being able to kill your own grandfather really bothers you, that i*s). There are many people who are interested in universes that include CTCs however, not because of the *time travel* applications, but simply because they are not impossible, and thus might be able to be included in a self consistent model of our universe.

From the paper:

This self-consistency requirement gives rise to a theory of closed timelike curves via entanglement and postselection, P-CTCs. P-CTCs are based on the Horowitz-Maldacena ‘‘final state condition’’ for black hole evaporation, and on the suggestion of Bennett [pdf] and Schumacher that teleportation could be used to describe time travel.

This is pretty neat stuff, that has gone through a few iterations within the quantum information community, most famously led by David Deutsch in 1991 with his *Quantum Mechanics Near Closed Timelike Lines*. Given my naiveté when it comes to QI, I’m just going to have to take the authors’ word for it that their model doesn’t, in fact, agree with Deutsch’s (although it is consistent within their framework). What is really neat though is that, because of the nature of postselection, it’s possible to do (and they did) a little *grandfather paradox* experiment with their model using P-CTCs and photons. Their “grandfather paradox circuit” is worth a look, if you’re interested. The argument is technical, and I can’t personally say I followed it thoroughly, but I can appreciate their (wonderfully worded) conclusions:

[S]uicidal photons in a CTC obey the Novikov principle: they cannot kill their former selves.

Our P-CTCs always send pure states to pure states: they do not create entropy. Hence, P-CTCs provide a distinct resolution to Deutsch’s unproved theorem paradox, in which the time traveler reveals the proof of a theorem to a mathematician, who includes it in the same book from which the traveler has learned it (rather, will learn it). How did the proof come into existence? Deutsch adds an additional maximum entropy postulate to eliminate this paradox. By contrast, postselected CTCs automatically solve it through entanglement: the CTC creates a random mixture of all possible ‘‘proofs.’’

So, they have a resolution to the grandfather paradox within P-CTCs. While theoretically, their model is inequivalent to Deutsch’s, experimentally, one can not distinguish the two, unfortunately. They also state that they “cannot test whether a general relativistic CTC obeys [their] theory or not,” which confuses me a little by the terminology, because CTCs don’t make sense as a concept outside of general relativity, so what a “non-general relativistic CTC” is vs. as “general relativistic CTC” is, I can’t say (I’m assuming they just mean a CTC in a distinctly curved spacetime, which would be very hard to work into an experiment).

For more, see Time Travel Without Regrets.

Hohm, O., & Kwak, S. (2011). Frame-like geometry of double field theory Journal of Physics A: Mathematical and Theoretical, 44 (8) DOI: 10.1088/1751-8113/44/8/085404

The abstract:

We relate two formulations of the recently constructed double field theory to a frame-like geometrical formalism developed by Siegel. A self-contained presentation of this formalism is given, including a discussion of the constraints and its solutions, and of the resulting Riemann tensor, Ricci tensor and curvature scalar. This curvature scalar can be used to define an action, and it is shown that this action is equivalent to that of double field theory.

This is still in my “to read” list, but I thought I’d mention it as double field theory has a little bit of buzz right now, that makes it worth a look. I do find it curious though, that there seems to be several incredibly similar papers to the above on this topic, by the same authors, but I’m going to go with the most recent one.

Carlo Rovelli (2011). Lectures on loop gravity arXiv arXiv: 1102.3660v2

The abstract:

This is a preliminary version of the introductory lectures on loop quantum gravity that I will give at the quantum gravity school in Zakopane. The theory is presented in self-contained form, without emphasis on its derivation from classical general relativity. Dynamics is given in the covariant form. The approximations needed to compute physical quantities are discussed. Some applications are described, including the recent derivation of de Sitter cosmology from full quantum gravity.

As if this needs explanation: Carlo Rovelli, one of the physicists who impresses me the most, has a great introduction to loop quantum gravity online (that is being updated currently). For anyone interested in the topic but wondering how to start, I imagine this is *the* recommendation now.

The *romantic* doubly-special Valentine:

The platonic BF theory Valentine:

And finally, the awkward and sexual cosmic censorship Valentine:

Happy Valentine’s Day

]]>For more, see NASA’s Hubble Finds Most Distant Galaxy Candidate Ever Seen in Universe.

M. Vardanyan, R. Trotta, & J. Silk (2011). Applications of Bayesian model averaging to the curvature and size of the Universe arXiv arXiv: 1101.5476v1

For more, see New Model Says the Cosmos Is At Least 250 Times Larger Than the Visible Universe.

John Kormendy, & Ralf Bender (2011). Supermassive black holes do not correlate with dark matter halos of galaxies Nature 469, 377 (2011) arXiv: 1101.4650v1

For more, see Dark matter does not act as a growth factor.

D. M. Webber et al. (MuLan Collaboration) (2011). Measurement of the Positive Muon Lifetime and Determination of the Fermi Constant to Part-per-Million Precision Physical Review Letters, 106 (4) DOI: 10.1103/PhysRevLett.106.041803

For more, see How Strong Is the Weak Force? New Measurement of the Muon Lifetime.

Igor I. Smolyaninov (2011). Virtual Black Holes in Hyperbolic Metamaterials arXiv arXiv: 1101.4625v1

For more, see Physicist Discovers How To Make Quantum Foam In A Test Tube.

Kirill Krasnov (2011). Gravity as a diffeomorphism invariant gauge theory arXiv arXiv: 1101.4788v1

]]>Geneva, 31 January 2011. CERN today announced that the LHC will run through to the end of 2012 with a short technical stop at the end of 2011. The beam energy for 2011 will be 3.5 TeV. This decision, taken by CERN management following the annual planning workshop held in Chamonix last week and a report delivered today by the laboratory’s machine advisory committee, gives the LHC’s experiments a good chance of finding new physics in the next two years, before the LHC goes into a long shutdown to prepare for higher energy running starting 2014.

The LHC was previously scheduled to run to the end 2011 before going into a long technical stop necessary to prepare it for running at its full design energy of 7 TeV per beam. However, the machine’s excellent performance in its first full year of operation forced a rethink. Expected performance improvements in 2011 should increase the rate that the experiments can collect data by at least a factor of three compared to 2010. That would lead to enough data being collected this year to bring tantalising hints of new physics, if there is new physics currently within reach of the LHC operating at its current energy. However, to turn those hints into a discovery would require more data than can be delivered in one year, hence the decision to postpone the long shutdown. If there is no new physics in the energy range currently being explored by the LHC, running through 2012 will give the LHC experiments the data needed to fully explore this energy range before moving up to higher energy.

See the interview with Rolf Heuer and Steve Myers on the decision. In related news, the the LHC’s winter shutdown is almost over.

Update: For a detailed discussion on the decision, see Tommaso Dorigo‘s piece, “The LHC Will Run At 7 TeV In 2011 And 2012“.

]]>The CMS on SUSY, Bill Unruh on simulated Hawking radiation, Ed Witten on knots, and Schenkel and Van Oystaeyen on noncommutative space(times):

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/c^{2}. 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.

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.

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:

Based on Witten’s record on such topics, and on a preliminary visual scan of the introduction, it would not be unreasonable to surmise that this preprint could change history. Khovanov homology will never look the same again. …This is trully a momentous occasion for knot theory!

For more, see Newsflash: Witten’s new preprint.

Alexander Schenkel (2011). Quantum Field Theory on Curved Noncommutative Spacetimes arXiv arXiv: 1101.3492v2

The basic concepts from the paper:

Noncommutative (NC) geometry provides a rich mathematical framework to modify the standard formalism of quantum field theory (QFT) in order to include quantum effects of spacetime

itself. … we collect the required tools from Drinfel’d twists and their associated NC geometry… We define an action functional for a real and free scalar field on twist-deformed curved spacetimes … and derive the corresponding deformed wave operator. … The deformed Green’s operators are constructed… to construct the space of real solutions of the deformed wave equation …The quantization is performed… “

And the important conclusions:

We have shown that the deformed symplectic R[[l ]]-module is isomorphic, via symplectic isomorphisms, to the formal power series extension of the undeformed symplectic vector space.

A direct consequence of this symplectic isomorphism for the deformed QFT is that it is ∗-algebra isomorphic to the formal power series extension of the undeformed QFT. This immediately yields isomorphisms between the corresponding groups of symplectic automorphisms and bijections between

the corresponding spaces of algebraic states.

Noncommutative spacetimes, or spaces, for that matter, are not things I have spent much time looking at, so I honestly can’t speak to the real content of this paper, other than by saying that there is growing interest in QFT on noncommutative spacetimes and those in quantum gravity should perhaps take note of it.

This isn’t about new research, per se, but Fred Van Oystaeyen has an interesting article on noncommutative space that is worth a read.

]]>So this isn’t physics*, but if you squint hard enough, you can probably make a connection. The hot topic today is Ken Ono‘s latest work on the partition function:

Ken Ono, Amanda Folsom, & Zach Kent (2011). l-adic properties of the partition function American Institute of Mathematics.

Ken Ono & *Jan Bruinier* (2011). AN ALGEBRAIC FORMULA FOR THE PARTITION FUNCTION American Institute of Mathematics.

*A **EurekAlert *press release appeared today, entitled: New math theories reveal the nature of numbers and people are already whispering *“Fields Medal”.* Now, I haven’t thoroughly read the paper yet, but, since I’m not a number theorist, my commentary probably won’t change very much anyway. Obviously, like most press releases, this one is full of hyperbole and ridiculous sentences like, “the team was determined go beyond mere theories”, but the actual work being discussed is fascinating.

Now, when we talk about a partition function in the context of Ono’s work, we don’t mean the partition function that is familiar to most physicists, we mean what number theorists call a partition function.

In this setting, a *partition *is a way of representing a natural number [latex]n[/latex] as the sum of natural numbers (ie. for [latex]n = 3[/latex], we have three partitions, [latex]3[/latex], [latex]2 + 1[/latex], and [latex]1 + 1 + 1[/latex], independent of order). Thus, the *partition function*, [latex]p(n)[/latex], represents the number of possible partitions of [latex]n[/latex]. So, [latex]p(3) = 3[/latex], [latex]p(4) = 5[/latex] (for [latex]n = 4[/latex], we have: [latex]4[/latex], [latex]3 + 1[/latex], [latex]2 + 2[/latex], [latex]2 + 1 + 1[/latex], [latex]1 + 1 + 1 + 1[/latex]) , etc..

To be slightly more technical, from Ken Ono and Kathrin Bringman [1],

A partition of a non-negative integer n is a non-increasing sequence of positive integers whose sum is [latex]n[/latex].

The concept is straight forward, but how to obtain these partition numbers, in general, is actually no trivial matter.

The master of series, Leonhard Euler, worked on solving this problem, to less than fully satisfying results. Using the reciprocal of what is now called Euler’s function, we get the generator for [latex]p(n)[/latex] by this infinite product,

[latex]\sum_{n=0}^{\infty} p(n)q^n= \prod_{n=1}^{\infty}\frac{1}{1-q^n}[/latex].

Here, [latex]q^n[/latex] counts the number of ways to write, [latex]n = a_1 + 2a_2 + 3a_3 +\ldots[/latex], for [latex]a_i \in \mathbb{N}[/latex], where each number [latex]i[/latex] appears [latex]a_i[/latex] times.

Obviously, for large [latex]n[/latex], this can be unwieldy, and it doesn’t lead to an explicit formula, but as long as you didn’t need more than 200~ partition numbers, it was *okay*.

Mathematics had to wait until the early 1900s before anyone was to expand on Euler’s partition number generator, when Srinivasa Ramanujan made contact with G.H. Hardy. Ken Ono actually has a beautiful historical, and mathematical, account of the Ramanujan and Hardy story, called “The Last Words of a Genius” [pdf].

Ramanujan famously proved an unusual and surprising result that [2],

[latex]p(5n + 4) = 0 (mod 5)[/latex],

[latex]p(7n + 5) = 0 (mod 7)[/latex],

[latex]p(11n + 6) = 0 (mod 11)[/latex].

He was also responsible for the first attempt at an explicit, although not exact, formula for [latex]p(n)[/latex] with Hardy,

[latex]p(n)\sim\frac{exp(\pi\sqrt{2n/3})}{4n\sqrt{3}}[/latex] as [latex]n \rightarrow \infty[/latex].

A decade later, Hans Rademacher came up with an exact formula, involving a convergent series, Dedekind eta functions, and Farey sequences; it was computationally unpleasant, to say the least (and not worth TeXing in here, but see Wikipedia if interested). It was also not *substantially *more useful than Euler’s initial work (although more direct).

In 2007, Ono was an author of a paper [1] that provided an arithmetic reformulation of Rademacher’s formula, using a Maass–Poincaré series. Based on some discussion, it wasn’t a giant improvement over Rademacher work.

It seems that since Euler initially came up with his generating function, there haven’t been major leaps in our understanding of partition numbers.

Apparently that all changes tomorrow. Ken Ono and colleagues, Jan Bruinier, Amanda Folsom and Zach Kent, will be announcing results that include a finite, algebraic formula for partition numbers thanks to the discovering that partitions are *fractal. *Well, so what does this mean, for partition numbers to be fractal?

Ken Ono, in the press release:

The sequences are all eventually periodic, and they repeat themselves over and over at precise intervals.

Alright, so obviously without going deeply into paper we can’t go further here (check out the pdf), but one can see how this insight could make the generation of partitions simple and explicit. This also, apparently, explains, and is linked to, Ramanujan’s *congruences* above. How? Well, they’re part of this *pattern*.

Ken Ono, in the press release:

I can take any number, plug it into P, and instantly calculate the partitions of that number. P does not return gruesome numbers with infinitely many decimal places. It’s the finite, algebraic formula that we have all been looking for.

Cool.

There is already an extension on the Ono-Folsom-Kent fractal issue by John Webb called, “An improved “zoom rate” for the Folsom-Kent-Ono l-adic fractal behavior of partition values” [pdf here].

*The physics tie in? Alright, so this is reaching, but here we go. Partitions are visualized using Young tableaus, and anyone in particle physics (see pdf for relevant introduction) has probably come across this, as well as other forms of group representation theory. Could an ability to always explicitly write down partition numbers translate to physics? I couldn’t ever imagine using groups so large that this could at all come into play… but, one could possibly draw some *conclusions* about the *fractal* nature of… ah, I give up.

Update: Comments on connections to actual physics can be found here.

[1] KATHRIN BRINGMANN, & KEN ONO (2007). An arithmetic formula for the partition function Proceedings of the American Mathematical Society, 135, 3507-3514

[2]Ken Ono (2010). The Last Words of a Genius Notices of the American Mathematical Society, 57, 1410-1419

[3] Folsom A, & Ono K (2008). The spt-function of Andrews. Proceedings of the National Academy of Sciences of the United States of America, 105 (51), 20152-6 PMID: 19091951

[4]Ken Ono, & Jan H. Bruinier (2009). Identities and congruences for the coefficients of Ramanujan’s omega(q) Ramanujan Journal

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