Scientific Series

Most predictions for binary compact object formation are normalized to the present-day Milky Way population. In this talk, I suggest the merger rate of black hole binaries could be exceptionally sensitive to the ill-constrained fraction of low-metallicity star formation that ever occurred on our past light cone. I discuss whether and how observations might distinguish binary evolution uncertainties from this strong trend, both in the near future with well-identified electromagnetic counterparts and in the more distant future via third-generation gravitational wave detectors.

A family of probability distributions (i.e. a statistical model) is said to be sufficient for another, if there exists a transition matrix transforming the probability distributions in the former to the probability distributions in the latter. The so-called Blackwell-Sherman-Stein Theorem provides necessary and sufficient conditions for one statistical model to be sufficient for another, by comparing their "information values" in a game-theoretical framework. In this talk, I will extend some of these ideas to the quantum case. I will begin by considering the comparison of ensembles of quantum states in terms of their "information value" in quantum statistical decision problems. In this case, I will prove that one ensemble is "more informative" than another if and only if there exists a suitable processing of the former into the latter. I will then move on to the comparison of bipartite quantum states in terms of their "nonlocality value" in nonlocal games. In this case, I will prove that one bipartite state is "more nonlocal" than another if and only if the former can be transformed into the latter by local operations and shared randomness, arguing, moreover, that the framework provided by nonlocal games can be useful in understanding analogies and differences between the notions of quantum entanglement and nonlocality.

I will discuss the geometry of heterotic string compactifications with fluxes. The compactifications on 6 dimensional manifolds which preserve N=1 supersymmetry in 4 dimensions must be complex manifolds with vanishing first Chern class, but which are not in general Kahler (and therefore not Calabi-Yau manifolds) together with a vector bundle on the manifold which must satisfy a complicated differential equation. The flux, which can be viewed as a torsion, is the obstruction to the manifold being Kahler. I will describe how these compactifications are connected to the more traditional compactifications on Calabi-Yau manifolds through geometric transitions like flops and conifold transitions. For instance, one can construct solutions by flopping rational curves in a Calabi-Yau manifold in such a way that the resulting manifold is no longer Kahler. Time permitting, I will discuss open problems, for example the understanding of the the moduli space of heterotic compactifications and the related problem of determining the massless spectrum in the effective 4 dimensional supersymmetric field theory. The study of these compactifications is interesting on its own right both in string theory, in order to understand more generally the degrees of freedom of these theories, and also in mathematics. For instance, the connectedness between the solutions is related to problems in mathematics like the conjecture by Mile Reid that complex manifolds with trivial canonical bundle are all connected through geometric transitions.

The 7 TeV LHC run has the potential to shed light on extensions beyond the Standard Model. I will discuss the prospects for finding new colored particles in an optimistic signature for discovery, heavy flavor jets and missing energy. I will illustrate the use of Simplified Models in guiding the organization of searches and presentation of results. Finally, I will discuss finer jet observables, and their possible applications in understanding Standard Model backgrounds and distinguishing new physics in a jet-rich environment.

I will introduce the gravitational microlensing, its application to the compact dark matter detection and the extra-solar planet observations. EROS has been performed the microlensing observation in four directions of the Galactic plane, away from the Galactic center. I will report the observational results and the interpret the data within the Standard Galactic model. As a result we extract the best fit to the dust contribution in the Galactic disk, orientation of the Galactic bar and the abundance of the red giants compare to local stellar distribution.

Supernovae observations strongly support the presence of a cosmological constant, but its value, which we will call apparent, is normally determined assuming that the Universe can be accurately described by a homogeneous model. Even in the presence of a cosmological constant we cannot exclude nevertheless the presence of a small local inhomogeneity which could affect the apparent value of the cosmological constant. Neglecting the presence of the inhomogeneity can in fact introduce a systematic misinterpretation of cosmological data, leading to the distinction between an apparent and true value of the cosmological constant. We establish the theoretical framework to calculate the corrections to the apparent value of the cosmological constant by modeling the local inhomogeneity with a $\Lambda LTB$ solution. Our assumption to be at the center of a spherically symmetric inhomogeneous matter distribution correspond to effectively calculate the monopole contribution of the non linear inhomogeneities surrounding us, which we expect to be the dominant one, because of other observations supporting a high level of isotropy of the Universe around us. By performing a local Taylor expansion we analyze the number of independent degrees of freedom which determine the local shape of the inhomogeneity, and consider the issue of central smoothness, showing how the same correction can correspond to different inhomogeneity profiles. Contrary to previous attempts to fit data using large void models our approach is quite general. The correction to the apparent value of the cosmological constant is in fact present for local inhomogeneity of any size, and should always be taken appropriately into account both theoretically and observationally.

String theory, famously, has a great many ground states. So many, in fact, that some argue that we should seek information in the statistical properties of these vacua, or worse, argue that we should abandon string theory as a theory with predictive power. On the other hand, very few vacua are known that look like the observed world of particle physics. In this talk I will review this situation and show that there are realistic models at the tip of the distribution of vacua, where topological complexity is minimised.

Wheeler's delayed choice (WDC) is one of the "standard experiments in foundations". It aims at the puzzle of a photon simultaneously behaving as wave and particle. Bohr-Einstein debate on wave-particle duality prompted the introduction of Bohr's principle of complementarity, ---`.. the study of complementary phenomena demands mutually exclusive experimental arrangements" . In WDC experiment the mutually exclusive setups correspond to the presence or absence of a second beamsplitter in a Mach-Zehnder interferometer (MZI). A choice of the setup determines the observed behaviour. The delay ensures that the behaviour cannot be adapted before the photon enters MZI. Using WDC as an example, we show how replacement of classical selectors by quantum gates streamlines experiments and impacts on foundational questions. We demonstrate measurements of complementary phenomena with a single setup, where observed behaviour of the photon is chosen after it has been already detected. Spacelike separation of the setup components becomes redundant. The complementarity principle has to be reformulated --- instead of complementarity of experimental setups we now have complementarity of measurement results. Finally we present a quantum-controlled scheme of Bell-type experiments. To reach any of these conclusions in either classical or quantum setting a (simple) hidden variable model that represents the "reality" of "particle" and "wave" should be analyzed. The model is never fully exorcised but just pushed to have more and more conspiratorial set of assumptions.

For stationary black holes it is universally agreed that entropy is proportional to horizon area. It is not so clear what the relationship is for dynamical black holes. In such spacetimes the event horizon is teleologically defined while the apparent horizon is non-unique. Thus even if one believes that entropy continues to be well-defined and proportional to horizon area, there are many possible areas to choose from. In this work I will review some recent work that I have done with M. Heller, G. Plewa and M.Spalinski that examines this issue from the perspective of the fluid-gravity correspondence. In this quasi-equilibrium regime the slowly evolving black brane horizons on the gravity side are dual to a perturbed fluid flow. The fluid manifestations of the various horizon definitions can be compared and the blackbrane mechanics is dual to hydro-thermodynamics. In particular, the uncertainty as to which is the "correct" horizon can be interpreted as dual to the inherent freedom in defining an entropy current.

We suggest the existence of a fundamental connection between baryonic and dark matter. This is motivated by both the stability of these two types of matter as well as the observed similarity of their present-day densities. A unified genesis of baryonic and dark matter arises naturally in models in which proton stability is ensured by promoting the baryon number to a local symmetry. This is illustrated in a specific class of SUSY models using the Affleck-Dine mechanism. The dark matter candidate in these scenarios is charged under the baryon gauge symmetry and is required to have a mass at the weak scale. We discuss the collider constraints from B-factories, LEP, Tevatron, and LHC, as well as direct detection bounds. A baryonic dark force is shown to be consistent with all data for mediators as light as the GeV scale.

I'll discuss how to systematically construct a (d+2)-dimensional solution of the vacuum Einstein equations that is dual to a (d+1)-dimensional fluid satisfying the incompressible Navier-Stokes equations with specific higher-derivative corrections. The solution takes the form of a non-relativistic gradient expansion that is in direct correspondence with the hydrodynamic expansion of the dual fluid. The dual fluid has nevertheless an underlying description in terms of relativistic hydrodynamics, with the unusual property of having a vanishing equilibrium energy density. Using the gravitational results, as well as an interesting and exact constraint on its stress tensor, we identify the transport coefficients of the dual fluid. A simple Lagrangian model is sufficient to realise its key properties.

A charged particle can detect the presence of a magnetic field confined into a solenoid. The strength of the effect depends only on the phase shift experienced by the particle's wave function, as dictated by the Wilson loop of the Maxwell connection around the solenoid. In this seminar I'll show that Loop Gravity has a structure analogous to the one relevant in the Aharonov-Bohm effect described above: it is a quantum theory of connections with curvature vanishing everywhere, except on a 1d network of topological defects. Loop states measure the flux of the gravitational magnetic field through a defect line. A feature of this reformulation is that the space of states of Loop Gravity can be derived from an ordinary QFT quantization of a classical diffeomorphism-invariant theory defined on a manifold. I'll discuss the role quantum geometry operators play in this picture, and the perspective of formulating the Spin Foam dynamics as the local interaction of topological defects.