John Donoghue's web pages

Congratulations again to Ufuk

donoghue — Wed, 18 Jul 2012 20:34:47 +0000

Ufuk Aydemir successfully defended his thesis today – I was his research advisor. His thesis contained three topics on physics beyond the standard model. He wrote about the tests of general covariance that was done with me and Mohamed Anber, on work with Lorenzo Sorbo on dynamical four-form fields, and also recent work on self-healing and new physics in effective field theories. His publications are here, and there are still more in the works. Congratulations Ufuk – the new Dr. Aydemir!

Field Theory and Gravitation

donoghue — Thu, 10 May 2012 23:48:32 +0000

I recently returned from giving some lectures at the 6th School on Field Theory and Gravitation in Petropolis, Brazil. The link is here. It had some good people at it and of course had an interesting topic. I also got to visit my former student Gustavo Burdman, who is doing very well at the University of Sao Paulo. It was good to see him after many years.

Congratulations, Ufuk

donoghue — Tue, 27 Mar 2012 23:28:09 +0000

My student Ufuk Aydemir has just been offered (and will accept) a nice postdoctoral position at Virginia Tech. This is great news, and the group at VT should be a good match for Ufuk’s skills. We are looking forward to great things.

Unitarity violation

donoghue — Tue, 27 Mar 2012 23:25:27 +0000

Ufuk Aydemir, Mohamed Anber and I have just put out a paper that shows that the traditional signal for new physics – the violation of unitarity at tree level – is actually unconnected to the onset of the new degrees of freedom. Moreover, in the chiral theory it is even very far from being an upper bound, because tree-unitarity violation happens almost an order of magnitude before the QCD degrees of freedom are manifest. We also have a very interesting gravitational example.

Running gravitational coupling

donoghue — Sat, 18 Feb 2012 21:52:58 +0000

This post is a bit late. Mohamed Anber and I have written a paper that provides counter-examples to the idea that there is a running gravitational coupling. Here is the link. We feel that this is a crucial rebuttal to the idea of a running gravitational coupling in the perturbative region. If this problem extends past the Planck scale, then it would seem that there would be problems for the idea of Asymptotic Safety.

Neutrinos faster than light?

donoghue — Sun, 09 Oct 2011 02:14:49 +0000

Mohamed and I were ahead of our time. Our paper back in the spring, The emergence of a universal limiting velocity,, about particles having different limiting velocities is now pretty relevant given the new OPERA result. However, not too many folks were paying attention to such a topic back then, so it was not noticed. We describe something that is overlooked in most of the discussion – the limiting velocities are scale-dependent quantities that “run” with the energy.

In our paper we stated that the largest deviation would come with the particles that are the weakest coupled- and pointed to gravitons as the weakest. We missed an opportunity to note that neutrinos are the second weakest! In light of the OPERA results, Mohamed and I have written a new paper where we directly address the neutrino situation – Limiting velocities as running and superluminal neutrinos. Hopefully people are paying more attention now. However, this running does not solve all problems with the OPERA result. It could be part of the solution should the OPERA result hold up.

Back from sabbatical

donoghue — Tue, 02 Aug 2011 18:16:26 +0000

While sabbatical is ideal as a way to work, I am now back in Amherst, working with my students and looking forward to the Fall semester.

Seminar in auditorium A

donoghue — Tue, 21 Jun 2011 20:02:17 +0000

I am visiting the Niels Bohr Institute this month and had the pleasure of giving a seminar in the historic Auditorium A. You can find many pictures of Bohr and famous physicists in this room – an example is above. The room has been kept in almost the same condition as back in Bohr’s day, with the same benches, lights etc. Most of the time, European science departments have moved out of the historic buildings to modern ones, so we have lost the sense of place for our history. NBI is different – the original buildings are still in use, as is Bohr’s office, the room where Heisenberg first came up with the uncertainty principle, and the seminar rooms. I enjoy this connection. Moreover, the folks here successfully keep up Bohr’s spirit of informality and relaxed discussion.

Last Thursday, Andy Jackson gave an interesting talk on the travels of an earlier famous Danish physicist, Hans Christian Ørsted, who discovered that electricity and magnetism were part of the same force. Andy and his wife have spent many years editing Ørsted’s letters and have many great stories to tell. The previous week I also had a chance to visit the island associated with yet an earlier Danish scientist – Tycho Brahe. Tycho was given an island (Hven) in the Øresund for his observatory. He hired many craftmen and assistants – it was the first big science laboratory. You can still see his instruments (above) although the associated castle is gone. That is me below helping Tycho scan the sky. Overall – interesting science tourism!

Koushik’s faculty job

donoghue — Tue, 24 May 2011 16:43:18 +0000

Congratulations to Koushik Dutta for his new faculty position at the Indian Institute of Science Education and Research in Bhopal, India! This is a new institute that India is investing in and Koushik sounds very excited by the new position. After graduation Koushik worked at the Max Planck Institute and DESY, and his goal has been just this – to obtain a faculty position in India. So we are all happy for his success.

Lunar Laser Ranging

donoghue — Fri, 29 Apr 2011 20:26:53 +0000

Thibault Damour and I have just put out a new paper on using Lunar Laser Ranging to test for spatial variations of the fundamental couplings. Recently there has been a paper which claims to find a spatial gradient in the fine structure constant. If the fine structure constant has a gradient, the mass of objects will be different in different locations since the mass depends on alpha, leading to a force in the direction of the gradient. And this effect will be different for different objects because of their different compositions. Amazingly, Lunar Laser Ranging is competitive for finding the gradient in alpha by measuring the differential forces on the earth and the moon, as they can now measure the distances to millimeter level precision! This work was a quick project using our past work on composition dependence. It was fun to learn many new aspects of the orbit problem from Thibault.