Neutron star physics, neutron star mergers, near-extremal black holes and effective theories near absolute zero.


This project involves using techniques from the AdS/CFT correspondence (known also as holography) to understand

(a) The non-trivial phases in the QCD phase diagram, involving non zero baryon number density as well as non-zero isospin density.

(b) The statics and dynamics in non-trivial phases relevant for neutron stars, where very low temperatures are relevant.

The holographic solutions dual to such phases involve near-extremal black holes that have unusual features compared to standard black holes: although for such solutions hydrodynamics

has been expected to break down, it was found that a modified form of hydrodynamics may be valid that was suggested by the thesis director and collaborators.

This type of effective theory is crucial in the description of the dynamics of neutron star mergers   as well as the GW and EM signals that one expects during mergers.

Moreover, quantum gravity effects persist sufficiently near extremality and the question is how they may affect the neutron star physics.


1) Concrete holographic solutions will be studied involving several types of near extremal black holes, with non-trivial baryon number and isospin energy density.

The charges that lead to extremality are QCD flavor charges like baryon number and isospin energy density.

2) The free energies and other thermodynamics data of such solutions will be calculated in order to draw the appropriate phase diagram and to characterise the phases and associated phase transitions.

3) The structure of the zero temperature limit of such solutions will be studied in detail in order to understand hydrodynamics and non-hydrodynamics poles in the associated energy-momentum two-point functions and their residues.

4) The important correlators needed for dynamical calculations associated with neutron star mergers are associated with energy-momentum correlators as well as flavor current correlators.

The IR limits of such correlators will be studied and their hydrodynamic approximation will be investigated in order to produce a reliable effective theory of such processes.

5) The possibility of quantum gravity effects, present in near extremal black holes will be investigated, and their implications for neutron star physics calculated.

6) The effect of all of the above to the evolution of neutron star mergers and neutrino transport (very important for the initial cooling stages of the proto-neutron star created after the merger will be

calculated and the implications for EM and GW signals analysed.

This project lies in the midst of an international effort to pin down all the physics associated to neutron stars, in which APC members are very active.


Elias Kiritsis






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