Astrophysics and Gravitation:
New Gravitational Lenses
Negrello, M., & et al. (2010). The Detection of a Population of Submillimeter-Bright, Strongly Lensed Galaxies Science, 330 (6005), 800-804 DOI: 10.1126/science.1193420
From the abstract:
We used early data from the Herschel Astrophysical Terahertz Large Area Survey to demonstrate that wide-area submillimeter surveys can simply and easily detect strong gravitational lensing events, with close to 100% efficiency.
Basically, the Herschel Survey is exceptionally good at determining when there is gravitational lensing occurring. This will be very useful for astrophysicists (but it’s not all that exciting right now).
Discovery of Unknown Structure in our Galaxy?
A press release this week from NASA’s Fermi Gamma-ray Space Telescope announced the discovery of a previously unseen, gamma ray “bubble”, structure in our galaxy, “a finding likened in terms of scale to the discovery of a new continent on Earth”.
Discoverer, Doug Finkbeiner, at the Harvard-Smithsonian Center for Astrophysics, said:
What we see are two gamma-ray-emitting bubbles that extend 25,000 light-years north and south of the galactic center… We don’t fully understand their nature or origin.
These “bubbles” aren’t completely foreign, as they do somewhat resemble the “gamma-ray fog” found in our galaxy, but the gamma rays here are much more energetic.
David Spergel at Princeton University:
Whatever the energy source behind these huge bubbles may be, it is connected to many deep questions in astrophysics.
For now, it’s a fun mystery for astrophysicists (but there is no need to jump on the “black hole explosion” bandwagon, as some have).
High Energy Physics and Particles:
First ZZ → 4μ event observed in CMS
Before the LHC ended its proton run for the year, the CMS released news of their first ZZ → 4μ event. This is exciting because it’s a very rare process (and further evidence that the LHC is on track). Other people are excited because, if the Higgs boson was a light Higgs, then the H→ ZZ → 4 leptons process would have a very clean signal that the CMS could see. This, however, doesn’t mean that this is what the CMS saw and most ZZ*/ZZ events probably have nothing to do with the Higgs, but they could, and that is always an exciting prospect.
Starting Heavy Ion Collisions in the LHC
On November 4th, 2010 proton running in the LHC at CERN came to a successful conclusion for the year. By November 7th, the transition to the lead ion run phase was almost complete, and the first collisions were recorded.
From the CERN press release:
Lead-ion running opens up an entirely new avenue of exploration for the LHC programme, probing matter as it would have been in the first instants of the Universe’s existence. One of the main objectives for lead-ion running is to produce tiny quantities of such matter, which is known as quark-gluon plasma, and to study its evolution into the kind of matter that makes up the Universe today. This exploration will shed further light on the properties of the strong interaction, which binds the particles called quarks, into bigger objects, such as protons and neutrons.
For more, see Heavy Metal in the Large Hadron Collider: this time for real, Large Hadron Collider (LHC) generates a ‘mini-Big Bang’, CERN completes transition to lead-ion running at the LHC, The LHC enters a new phase, Large Hadron Collider pauses protons; looks ahead to lead.
MiniBooNE Still Refusing to Go Quietly
Aguilar-Arevalo, A., & et al. (2010). Event Excess in the MiniBooNE Search for ν̅ μ→ν̅ e Oscillations Physical Review Letters, 105 (18) DOI: 10.1103/PhysRevLett.105.181801
Everyone’s favourite (or least favourite) anomalous neutrino oscillation results are in the news again. I don’t think anyone wants to casually jump on the idea of sterile neutrinos, but the MiniBooNE results still haven’t been explained away yet and they’re starting to gain more and more support. Perhaps we’ll have to wait for MiniBooNE’s followup, MicroBooNE, for answers.
General Relativity, Quantum Gravity, et al.:
Quantum Gravity Corrections for QED
David J. Toms (2010). Quantum gravitational contributions to quantum electrodynamics Nature 468:56-59,2010 arXiv: 1010.0793v1
This paper is probably the hot topic of the week because it’s good but some don’t think it’s quite good enough.
Quantum electrodynamics describes the interactions of electrons and photons. Electric charge (the gauge coupling constant) is energy dependent, and there is a previous claim that charge is affected by gravity (described by general relativity) with the implication that the charge is reduced at high energies. But that claim has been very controversial with the situation inconclusive. Here I report an analysis (free from earlier controversies) demonstrating that that quantum gravity corrections to quantum electrodynamics have a quadratic energy dependence that result in the reduction of the electric charge at high energies, a result known as asymptotic freedom.
The basic idea here is that gravity propagators have been added to one-loop diagram corrections (ie. using gravity to correct QED). As far as I can tell, this all looks like it was handled correctly, and no one is really objecting to that. However, some people are asking, “Is this actually that exciting?”. At first glance, working gravity into QED sounds like it should be a really big deal, but it’s not actually that large of a step forward, compared to the literature that has come before it (some by Toms). Is this being “over hyped?” Well, only if you consider publishing in Nature “hype”. Frankly, I’m thrilled to see Nature publishing articles related to quantum gravity. Who cares that this didn’t resolve anything major, there are very, very, very few, credible, major leaps within QG/HEP theory these days, and we should take successes where we can get them.
Weinberg on Ultraviolet Divergences in Cosmological Correlations
Steven Weinberg (2010). Ultraviolet Divergences in Cosmological Correlations arXiv arXiv: 1011.1630v1
Technical and brilliant, in the usual way of Steven Weinberg, this paper presents us with a new method for dealing with pesky ultraviolet divergences, without the standard regularization pains.
From the introduction:
Much effort has been expended in recent years in the calculation of quantum effects on cosmological correlations produced during inflation. These calculations are complicated by the occurrence of ultraviolet divergences, which have typically been treated by the method of dimensional regularization. Unfortunately, this method has several drawbacks. It is difficult or impossible to employ dimensional regularization unless the analytic form of the integrand as a function of wave number is explicitly known, so calculations have generally relied on an assumption of slow roll inflation, or even strictly exponential inflation. Also, even where an analytic form of the integrand is known, dimensional regularization can be tricky.
While the method presented in this paper seems useful for one-loop correction functions, there may be some difficulty implementing it for multi-loop graphs (unsurprisingly). If we live in a universe where matter loops dominate over graviton loops (hey, we could), then we should all be happy!
Cambridge Lectures on Supersymmetry and Extra Dimensions
Sven Krippendorf, Fernando Quevedo, & Oliver Schlotterer (2010). Cambridge Lectures on Supersymmetry and Extra Dimensions arXiv arXiv: 1011.1491v1
This really isn’t any new knowledge, but it is a great looking lecture series for those interested in learning the technical side of supersymmetry in an accessible way.
These lectures on supersymmetry and extra dimensions are aimed at finishing undergraduate and beginning postgraduate students with a background in quantum field theory and group theory. Basic knowledge in general relativity might be advantageous for the discussion of extra dimensions. This course was taught as a 24+1 lecture course in Part III of the Mathematical Tripos in recent years. The first six chapters give an introduction to supersymmetry in four spacetime dimensions, they fill about two thirds of the lecture notes and are in principle self-contained. The remaining two chapters are devoted to extra spacetime dimensions which are in the end combined with the concept of supersymmetry. Videos from the course lectured in 2006 can be found online at this http URL .
This Week in the Universe: November 2nd – November 8th by PLOS Blogs Network, unless otherwise expressly stated, is licensed under a Creative Commons Attribution 4.0 International License.