Black Hole Microstate and de Sitter Landscapes in String Theory – Black-dS-String

String Theory is the most promising candidate for a theory that unifies all the forces that exist in nature, and could therefore provide a framework from which one may hope to derive all the observed physical laws. However, String Theory lives in ten dimensions, and to obtain real-world physics one needs to compactify it on certain six-dimensional compact spaces whose size is much smaller than any length scale accessible to observations. Since there is a plethora of such spaces, this is believed to result in a landscape (or Multiverse) of possible four-dimensional vacua - of order 10^{500} - that have all possible physical laws with all possible constants. This has led to many people arguing that the constants in the physical laws that we measure in our universe do not come from an underlying unified theory, but are environmental (anthropic) variables that are determined by where we are in this Multiverse. 

The first purpose of this project is to unequivocally establish whether a very large number of the phenomenologically relevant string theory solutions have to be discarded, either because they are unstable, or because they are ruled out by LHC. We plan to do this by a thorough revisit of the most common ways of obtaining solutions with a positive cosmological constant and/or containing extensions of the Standard Model in String Theory. 

String Theory is also a quantum theory of gravity, and as such it has given us several new ways to understand black holes and to attack difficult problems like Hawking's Information Paradox, which puts Quantum Mechanics and General Relativity into sharp conflict. Perhaps the boldest and definitely the most studied such paradigm, which comes from the convergence of String-Theory “fuzzball” calculations  and Information-Theory “firewall” arguments, argues that at the black hole horizon classical General Relativity stops being valid, and a new description in terms of non-perturbative string degrees of freedom takes over, which may result in a firewall for a free-falling observer. 

The past work of our groups has established that String Theory does have a mechanism to create a structure that can maintain itself at the horizon, and this mechanism makes critical use of the fluxes and extra dimensions present in String Theory. The purpose of this proposal to use this mechanism to explicitly construct horizonless microstate solutions that have the same mass and charge as a black hole, but differ from the classical black hole solutions at the scale of the horizon. This would solve Hawking's information paradox, and revolutionize our understanding of quantum gravity by establishing that the horizon of the black hole solutions found in General Relativity textbooks emerges as a thermodynamic approximations of a huge number of horizonless configurations, much like a continuous fluid gives a thermodynamic description of a huge number of configurations of molecules. 

These two research areas, although they belong to disjoint subfields of String Theory and have different aims, are in fact grounded in the same underlying physics. Their overall goal is to construct very large families of supergravity solutions with fluxes, either to describe the landscape of compactifications of string theory or the landscape of “black hole microstate” solutions. The key ingredient in these constructions is the same: adding, to supersymmetric solutions, branes or fluxes that carry opposite charge to that of the solution and break the supersymmetry. Hence, any progress that we make will have important implications for both areas of exploration.