לוח שנה משולב

It is by now well known that the AdS/CFT duality provides an interesting way of calculating anomalous dimensions at high spin, for a gauge theory at strong coupling. A high spin operator, made of adjoint fields, is represented by (or dual to) a rotating open string in anti-de Sitter space. The anomalous dimension shows up, in the string side of the correspondence, simply as the difference between string energy and spin. On the other hand it is also know that it is possible to introduce matter degrees of freedom - fields in the fundamental representation of the gauge group - in the AdS/CFT duality by introducing probe (flavour) branes. This approach leads to a nice description of meson states. So, a natural question to be asked is : can one calculate the anomalous dimension for operators in the fundamental representation, like a quark anti-quark, using AdS/CFT? This question will be the main issue of this seminar. We will see that the presence of an energy scale makes it a non trivial task the identification of a quantity representing, in the string side, the dimension of the gauge theory operator. Serching for the solution to this problem, we found a new entry in the dictionary of AdS/CFT: the anomalous dimension at high spin is proportional to the string proper length. Also, we found strong indications that, in the case of a non conformal duality, the operator properties are obtained from measurements made by a local observer (not sensible to energy scales) in the anti-de Sitter space, while the description of the states comes from a coordinate time observer. (reference: JHEP 1408, 104 (2014) at ArXiv:1405.7388)

Hydrodynamic instabilities are a primary impediment to the success of inertial confinement fusion (ICF), as they can severely degrade capsule performance [1]. Even with perfectly smooth capsules, the fill tube and capsule support provide perturbations that seed instabilities. Consequently,
understanding the evolution of perturbations and their effects on capsule performance is critical to the success of an ICF program. We discuss here the use of spectroscopic methods to diagnose the growth of hydrodynamic instabilities in imploding capsules. To understand capsule evolution and guide experimental design and interpretation, we use high-resolution HYDRA [2] simulations, postprocessed with Cretin [3], to simulate the spectra produced by capsules with specified initial perturbations. The
spectral simulations cover a wide range of conditions, from the multi-keV hot spot to the cold dense pusher.

For capsules with mid-Z dopants, the resulting X-ray spectrum can be analyzed to obtain information about the plasma conditions. An analysis of the dopant K-shell line emission has been used to estimate the mass of ablator material mixed into the hot spot [4]. Other spectral features can be used to provide information about the shell and further constrain the mixed mass. Other recent work has focused on using spectroscopy to quantitatively characterize the growth of perturbations. Capsules containing a small amount of argon in the gas produce sufficient emission before peak compression to provide radiographic information. The analysis of simulated spectra from capsules with machined perturbations demonstrates the possibility of extracting quantitative measures of perturbation growth.
References
[1] B.A. Hammel, et al, High Energy Density Physics, 6 (2010) 171.
[2] M. Marinak, et al, Phys. Plasmas 8 (2001) 2275.
[3] H.A. Scott, J Quant Spectrosc Radiat Transfer 71 (2001) 681.
[4] S.P. Regan et al. Phys. Rev, Lett. 111, 045001 (2013).