1.2021 - paper on the Hagedorn phase of fundamental strings
Given at: XXXV Max Born Symposium, Wroclaw, Poland, 7 - 12 September 2015
If a black hole (BH) is initially in an approximately pure state and it evaporates by a unitary process, then the emitted radiation will be in a highly quantum state. As the purifier of this radiation, the state of the BH interior must also be in some highly quantum state. So that, within the interior region, the mean-field approximation cannot be valid and the state of the BH cannot be described by some semiclassical metric. On this basis, I will present a model in which the state of the BH interior is described as a collection of a large number of excitations that are packed into closely spaced but single-occupancy energy levels; a sort-of “Fermi sea” of all light-enough particles. This highly quantum state is surrounded by a semiclassical region that lies close to the horizon and has a non-vanishing energy density. I'll show that such a state looks like a BH from the outside and decays via gravitational pair production in the near-horizon region at a rate that agrees with the Hawking rate. I also consider the fate of a classical object that has passed through to the BH interior and show that, once it has crossed over the near-horizon threshold, the object meets its demise extremely fast. This result cannot be attributed to a “firewall”, as the trauma to the in-falling object only begins after it has passed through the near-horizon region and enters a region where semiclassical spacetime ends but the energy density is still parametrically smaller than Planckian.
How black holes burn: firewalls, smoke and mirrors
Given at: KAVLI INSTITUTE FOR THEORETICAL PHYSICS, Feb 25, 2014
In several recent articles we have proposed a novel model of black hole (BH) evaporation that improves upon Hawking's model in three aspects: (i) The quantum fluctuations of the collapsing shell (or BH) spacetime are included as well as (ii) The time dependence of the emission process and (iii) The back-reaction on the BH by the emitted particles. In the seminar, I will present the model and use it to calculate the quantum state of the emitted radiation, the rate of information release during BH evaporation and the energy density near the BH horizon. Then I will explain how unitarity and the equivalence principle are respected within our model and show how the information paradox and the firewall problem are evaded.
Black hole paradoxes: The clash of quantum mechanics and gravity
Given at: Arnold Sommerfeld Center, August 2014
Observable signal of gravity waves in the cosmic microwave background from small field models of inflation
Given at: Perimeter Institute, June 2009