News
18/11/2011
The OPERA Collaboration has improved the most important factor for error, by running and collecting 20 extra neutrino events with shorter proton bunches from CERN. According to the paper posted today at the ArXiV, the speed of light discrepancy remains. Relativistic corrections to the path were estimated and found negligible.
2/10/2011
D. Christodoulou, distinguished professor at CCTP, was recently awarded the prestigious Shaw prize for the Mathematical Sciences, shared with Prof. R. S. Hamilton. The prize was given for their highly innovative works on nonlinear partial differential equations in Lorentzian and Riemannian geometry and their applications to general relativity and topology.
29/09/2011
An article by E. Kiritsis on superluminal propagation in string theory, published by the kathimerini newspaper, in view of the recent experimental claims on the speed of neutrinos.
23/09/2011
A remarkable claim has been made by the OPERA experiment, that takes a neutrino beam from CERN and studies its interactions inside the Gran Sasso laboratory in central Italy.
As described
in their paper http://fr.arxiv.org/abs/1109.4897 submitted to
the ArXiV, they have measured the velocity of the neutrinos and found it to be 2.5 X 10^(-5) times larger than that of light in vaccum, using a
clever technique proposed in http://arxiv.org/abs/0805.0253.
The result is more than 6 sigma away from the expected value of the velocity of neutrinos, namely the velocity of light.
The result is so unexpected that it will take some time untill it passes further scrutiny and is confirmed by other experiments.
It should be noted that Supernova 1987a data already excluded this state of affairs if the phenomenon is energy independed. However
as supernova neutrinos had an energy of about 10 MeV while OPERA neutrinos have 10 GeV, it suggests that the effect has quadratic dependence on energy and is therefore due to a non-renormalizable operator.
A potential loophole that has not obviously been considered is the use of general relativistic corrections to the path of neutrinos.
These may correct the result wich takes as the distance the straight line between emission and interaction points.
A simple newtonian simplified solvable model indicates that such corrections give an effective speed that is larger than
than the standard one. In Scwartzschild modeling of the gravitational field f the earth, the (small) parameter that controls the
gravitational corrections is x=GM/(Lc^2) where G is Newton's constant, M the mass of the earth, L is the length of the path (about 750 Km)
and c is the speed of light in vacuum. We expect the result to have a regular expansion in x. Putting the values of the various constants we obtain that x~10^(-8) and is probably too small to affect the result.
There are not many theoretical ideas on how to achieve this state of affairs from first principles assuming that the experimental result is correct.
Of course one could just postulate that the speed of neutrinos is different (larger) than c, but this is excluded by supernova data.
To make it compatible with such data , Lorentz invariance should be broken.
There is however another way that is possible: to have the SM live on a brane-world and the neutrinos to be able to travel in a warped bulk.
This phenomenon was found first as a side effect in a holographic study of the effective potential in N=4 superYM using probe branes by CCTP member E. Kiritsis in
hep-th/9906206. It was observed that on a brane, embeded in the background of other black branes, a velocity of light is induced on the brane, that is variable and depends on its position in the bulk. Moreover the velocity of light is smaller that that of the bulk. S. Alexander shortly afterwards provided some brane models
that stabilize such a velocity of light to arbirary small values. This line of ideas lend to the developement of the idea of
Mirage Cosmology.
Gubser, several years later generalized the proposal to geometries that are entropy-less.
Such geometries appear for example in holographic finite density saddle points.
A bit later and probably independently,
Chung and Freeze suggested that faster propagation outside of branes could be used to solve the horizon problem in cosmology. This subject was subsequently developed by Caldwell and Langlois.
Finally Gibbons and Herdeiro have shown in full generality that the speed of light on D-branes is always smaller or equal to that of the bulk.
This line of reasoning suggests that models where (a) the SM is living on a brane, and (b) neutrinos can move in a approapriately warped bulk can natuarally produce a superluminal speed for neutrinos.
Such models where entertained in the context of orientifold in string theory in
hep-ph/0004214
and in more detail in hep-th/0210263 by I. Antoniadis, E. Kiritsis, I. Rizos and T. Tomaras. In these works the foundations of the bottom-up approach to string theory model building were introduced.
The right-handed neutrinos were living in the bulk and they were mixing with the doublet neutrinos on the brane.
This could potentially provide a first principles model compatible with the OPERA data.
8/09/2011
CCTP researcher Takeshi Morita was honored with the "Young Scientist Award of the Physical Society of Japan" in 2011, for his contribution in http://arxiv.org/abs/arXiv:0910.4526 and related works. T. Morita and senior researcher V. Niarchos have also published recently a very interesting work where they verify the F-theorem in 3 dimensions and present an interesting condition for non-perturbative supersymmetry breaking.
30/05/2011
J. Iliopoulos, S. Glashow and L. Maiani have been awarded the 2011 prize of the European Physical Society for their work on the GIM mechanism. You can see the citation here. An interesting exposition of the history and issues surrounding the GIM mechanism can be found at the Scholarpedia.
27/11/2010
The first Pb-Pb heavy ion collisions at 2.76 TeV were succesful at LHC. The
ALICE experiment has already produced two papers
on Elliptic flow and charged multiplicities
There are several animations of the reconstruction of the first events here:
Animation 0
Animation 1
Animation 2
Animation 3
Animation 4
Animation 5
13/12/2009
The work of Center members and their European collaborators was recently highlighted in Physical Review Focus. The occasion was a recent high-precision lattice calculation by Marco Panero of the thermodynamic functions of SU(N) Yang Mills theory for different values of N. This study has shown that there is little variation of the thermodynamic functions with N, suggesting that string theory descriptions of the deconfined phase of Yang Mills theory, valid at large N, are close to the physics of the SU(3) theory relevant for the strong interactions. Moreover, the thermodynamic functions were compared successfully with predictions from a semi-phenomenological holographic model, developed earlier. Such a model has two extra adjustable parameters compared to Yang Mills, and can quantitatively reproduce 0^{++}, 0^{+-}, 2^{++} glueball spectra at zero temperature, the deconfining phase transition as well as the thermodynamic functions, and the spatial string tension at finite temperature.
12/12/2009
Το Κέντρο Θεωρητικής Φυσικής Κρήτης (Crete Center for Theoretical Physics) οργανώνει στις 27/02/2010 την ημερίδα International Particle Physics Masterclasses, σε συνεργασία με το European Particle Physics Outreach Group και το Ελληνικό του τμήμα Ελληνική Ομάδα Εκλαίκευσης". Για πληροφορίες ακολουθείστε τον σύνδεσμο.
An outreach day, is organized at the Physics Department on 27 February 2010. Its purpose is to bring the excitement of recent advances of High Energy Physics and of upcoming experiments at CERN to high school students from Crete. More information can be found here (in Greek)
10/11/2009
The Advisory Committee of the Center will visit during the week 17-20 November 2009.
They will consult with Center members on Wednesday and Thursday.
C. Callan will give the department colloquium on Thursday.
G. Veneziano will give the High Energy Physics Seminar on Friday.
16/09/2009
One of the
Center research papers has made it at position 43 into
SPIRES' 2008-2009 top-cited list (containing 57 papers with more than 50 citations).
The paper discusses the cosmology of Horava-Lifshitz gravity, a radically different theory of gravity proposed recently.
It has currently 96 citations, reflecting widespread scientific interest in this new theory.
15/09/2009
The Center starts its postdoctoral campaign for the 2010 academic year.
We will have at least one and possibly more postdoctoral positions in the areas of particle physics and cosmology.
Deadline for applications is 1 December 2009.
More information can be found at job opportunities
16/05/2009
The Center is open to application of candidates for the European Marie Curie Fellowships.
Deadline is 30 June 2009. Deadline for the EU is 18 August 2009.
More information can be found at job opportunities
16/05/2009
The Center is looking for a part-time secretary. Here is the
announcement and details. Deadline is 31 May 2009.
18/04/2009
Το Κέντρο, σε συνεργασία με το Τμήμα Φυσικής, διοργανώνει την 13η Ιουνίου, εσπερίδα διαλέξεων απευθυνόμενη στο ευρύ κοινό, για να γιορτάσει τη συμπλήρωση 30 χρόνων από την δημιουργία του τμήματος Φυσικής.
Τρεις διάσημοι Έλληνες Φυσικοί έχουν προσκληθεί για να παρουσιάσουν τις μοντέρνες θεωρητικές ιδέες στη Φυσική Υψηλών Ενεργειών και την Kοσμολογία καθώς και τα μεγάλα σύγχρονα πειράματα που ερευνούν τα μυστικά της φύσης στα όρια της σημερινής γνώσης!
Περισσότερες πληροφορίες μπορούν να βρεθούν στην αντίστοιχη ιστοσελίδα.
15/03/2009
An outreach day, is organized at the Physics Department on 21 March. It purpose is to bring the excitement of recent advances of High Energy Physics and of upcoming experiments at CERN to high school students from Crete. More information can be found here (in Greek)
22/02/2009
An informal workshop will be organized 8-12 May. More information can be found at Conferences
15/01/2009
The 5th Crete Regional Meeting on String Theory will take place in Kolymbari, 28 June-6 July 2009. More information can be found at Conferences
15/01/2009
Our postdoctoral campaign has finished for the current academic year. Details can be found at Jobs
15/10/2008
Several research positions are open. Details can be found at Jobs