Winter 2014

In this talk, I introduce an alternate framework for dark-matter physics which we call "Dynamical Dark Matter" (DDM). Within this framework, the requirement of dark-matter stability is replaced by a balancing of lifetimes against cosmological abundances across an ensemble of individual dark-matter components with different masses, lifetimes, and abundances. It is this DDM ensemble which collectively serves as the dark-matter "candidate" within the DDM framework, and which collectively carries the observed dark-matter abundance \Omega_{CDM}. Likewise, it is the balancing between lifetimes and abundances across the ensemble as a whole which ensures the phenomenological viability of the DDM framework --- indeed, the usual notion of dark-matter stability is no longer required. As we shall discuss, this leads to a highly dynamical cosmology in which quantities such as Omega_{CDM} experience non-trivial time-dependences beyond those associated with the expansion of the universe. DDM ensembles arise naturally in many extensions to the Standard Model, including string theory and theories with large extra spacetime dimensions. Moreover, the DDM framework can lead to many striking signatures at colliders as well as at direct- and indirect-detection dark-matter experiments --- signatures which transcend those usually associated with traditional dark-matter candidates. In this talk I shall give a theoretical overview of the DDM framework, and survey the research which has been done in this field thus far.

4-dimensional conformal field theories (CFTs) with N=2 superconformal symmetry have moduli spaces of vacua with spontaneously broken scale invariance which whose geometry is tightly constrained. All possible such geometries whose Coulomb branches are homeomorphic to a plane are constructed, and the global flavor symmetries of the associated CFTs are deduced. There are ten such CFTs, one of which was not found before by previous methods. We also construct examples of more exotic 1-complex-dimensional Coulomb branches with more complicated complex structures, but do not classify them.

The neutron's unique properties enable high measurement precision at extremely low energies, making it a well suited probe to search for diluted traces of physics that dominated the very early Universe. In the next few years a boost in statistical quality of experiments by more than two orders of magnitude is expected by super-thermal sources of ultra-cold neutrons (UCN) at various facilities. A prominent experiment using UCN is the search for the neutron’s electric dipole moment (EDM) using spin-clock comparisons combined with Ramsey’s method of separated oscillatory fields. Such an EDM would be a manifestation of yet unknown broken symmetries above the TeV scale and an important ingredient to explain the matter-antimatter asymmetry in the Universe in most theories beyond the SM. An example of a related technological development is the magnetic environment, providing the world's smallest existing magnetic field over a large volume. Another scientific highlight is the realization of a gravity-resonance spectroscopy technique, a first step towards a Ramsey-like experiment without electromagnetic interactions. Here, quantized states of neutrons confined by gravity have transitions excited by vibrating mirrors. These experiments benefit from the small charge radius of the neutron that conceptually gives access to effects occurring at short distances, e.g. new gravity-like forces or spin-matter couplings. In addition to an overview of this field of research, I will discuss selected recent developments with potentially large impact, once the new facilities are available.

Stars realize a variety of physical conditions inaccessible in the lab. Various stages of stellar evolution are influenced by microphysical processes that are sensitive to the fundamental properties of elementary particles. This makes it possible to use them as particle physics laboratories. Until recently, stars of 5-10 solar masses were not considered particularly useful for particle physics. I will discuss how the evolution of these stars can be qualitatively changed by neutrino magnetic moments or axion emission. In particular, the mere existence of Cepheid variable stars turns out to provide world’s best bound on the axion-photon coupling in a broad range of parameters.

In this talk I present a scenario of high-scale supersymmetry where the gauginos are Dirac fermions. Picking the supersymmetry-breaking scale wisely, we can accommodate both mH = 126 GeV and gauge coupling unification. The only TeV-scale particle in the spectrum is the Higgsino, which can potentially serve as Dark Matter.

The next run of the LHC potentially will provide information about new physics connected to dark matter. I will discuss recent work aimed at classifying dark matter collider signals from a bottom-up approach, in particular in the context of monojet and related searches. This has led to strong constraints on certain kinds of interactions, as well as possible new avenues for probing dark matter physics with the LHC. I will focus on a few examples, including production associated with heavy quarks and production associated with a Higgs boson.

I discuss the implications of the 126 GeV Higgs boson discovery for natural extensions of the Standard Model. In composite Higgs models, light fermionic top partners often play a role in obtaining a light Higgs mass. These are typically accompanied by massive gluon partners which can contribute sizeable radiative corrections to the Higgs mass, thereby easing the tension of having a light Higgs with heavy top partners. On the other hand if the Higgs is elementary, supersymmetric models with light stops and gluinos require new contributions to the Higgs mass. In the NMSSM with a large singlet-Higgs coupling this relieves the usual tuning in the Higgs vacuum expectation value. However, new sources of tuning from the Higgs mass and the Higgs couplings further constrain the naturalness of the model, implying that the natural region of NMSSM parameter space will be fully explored during Run-II of the LHC.

Moonshine is a mysterious set of relationships between different fields of mathematics -- number theory, representation theory, and (most recently) algebraic geometry -- explained by their connections to certain special solutions of string theory. In this introductory talk we explain the basic objects involved as well as the original Monstrous moonshine conjectures (now proven). We also sketch recent extensions to more physically interesting solutions of string theory, such as compactifications on K3 surfaces and Calabi-Yau manifolds. The talk is designed to be accessible to a typical high energy theory audience.

I will discuss theoretical progress in understanding properties of the Higgs boson, and their effects on future experimental studies. Topics will include how to reduce the theoretical uncertainties currently affecting Higgs coupling measurements, and what can be learned at a high-luminosity LHC from rare Higgs decays.

Time crystals are a class of systems admitting spontaneous breaking of time-translation symmetry. The quantization of time crystals poses special challenges, which require modifications to standard quantization prescriptions. Possible applications to condensed matter and cosmology will be discussed.

Four dimensional N=1 supersymmetric gauge theory with gauge group SU(N_c) and matter in the adjoint and fundamental representations gives rise to a series of fixed points with an ADE classification. I will review what's known about their dynamics, present some new results, and discuss some outstanding challenges.

Higher spin gravity theories in Anti-de Sitter space have been conjectured to be holographically dual to conformal field theories with vector-like matter fields: in the simplest version of the duality, these are just free CFT's of N-component massless scalars or fermions. After reviewing these conjectures, I will discuss recent new tests of the duality based on comparing the bulk and boundary partition functions. In particular, I will show that the sum over one loop free energies of the infinite set of massless higher spin gauge fields in AdS_{d+1} is precisely consistent with the form of the O(N^0) term in the partition function of the CFT on S^d and S^1xS^{d-1}.