Bootstrapping the O(N) Vector Models
David Simmons-Duffin Institute for Advanced Study (IAS)
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Orbifolds and topological defects
Daniel Plencner Ludwig-Maximilians-Universitiät München (LMU)
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The local Callan-Symanzik equation: structure and applications
Boaz Keren-Zur L'Ecole Polytechnique Federale de Lausanne (EPFL)
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Orbifold partition function and their phases
Daisuke Yokoyama Seoul National University
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Fundamental Physics with Optically Levitated Dielectric Objects
Asimina Arvanitaki Perimeter Institute
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Hexagon functions and six-gluon scattering in planar N=4 super-Yang-Mills
Lance Dixon Stanford University
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Bootstrapping the O(N) Vector Models
David Simmons-Duffin Institute for Advanced Study (IAS)
We study the conformal bootstrap for 3D CFTs with O(N) global symmetry. We obtain rigorous upper bounds on the scaling dimensions of the first O(N) singlet and symmetric tensor operators appearing in the \phi_i x \phi_j OPE, where \phi_i is a fundamental of O(N). Comparing these bounds to previous determinations of critical exponents in the O(N) vector models, we find strong numerical evidence that the O(N) vector models saturate the bootstrap constraints at all values of N. We also compute general lower bounds on the central charge, giving numerical predictions for the values realized in the O(N) vector models. We compare our predictions to previous computations in the 1/N expansion, finding precise agreement at large values of N. -
Including astroparticle observables in global fits to new physics scenarios
Patrick Scott McGill University
Searches for physics beyond the standard model come in many forms, from terrestrial probes to astroparticle experiments and cosmological observations. Efforts to combine multiple search channels in 'global fits' to new physics scenarios typically consider only a subset of the available channels. Astroparticle searches in particular are usually only included in a very approximate way, if at all. In this talk I will review recent progress in including detailed gamma-ray, neutrino and CMB searches for dark matter in global fits. I will also preview some of the future developments and challenges in this field, where the applicability of global fits will move well beyond the small range of constrained supersymmetric models they have so far mostly been applied to. -
Electroweak Cogenesis and a CP Violating Higgs Boson
We propose a simple renormalizable model of baryogenesis and asymmetric dark matter generation at the electroweak phase transition. Our setup utilizes the two Higgs doublet model plus two complex gauge singlets, the lighter of which is stable dark matter. The dark matter is charged under a global symmetry that is broken in the early universe but restored during the electroweak phase transition. Because the ratio of baryon and dark matter asymmetries is controlled by model parameters, the dark matter need not be light. Thus, new force carriers are unnecessary and the symmetric dark matter abundance can be eliminated via Higgs portal interactions alone. The dark matter mass is also constrained within a window around the weak scale. One of the main predictions of this model is CP violating Higgs signals at the LHC and future colliders. -
Orbifolds and topological defects
Daniel Plencner Ludwig-Maximilians-Universitiät München (LMU)
Orbifolding a 2-dimensional quantum field theory by a symmetry group admits an elegant description in terms of defect lines and their junction fields. This perspective offers a natural generalization of the concept of an orbifold, in which the role of the symmetry group is replaced by a defect with the structure of a (symmetric) separable Frobenius algebra. In this talk I will focus on the case of Landau-Ginzburg models, in which defects are described by matrix factorizations. After introducing the generalized twisted sectors and discussing topological bulk and boundary correlators in these sectors, I will present a simple proof of the Cardy condition and discuss some further consistency checks on the generalized orbifold theory. This talk is based on arXiv:1307.3141 with Ilka Brunner and Nils Carqueville. -
The Era of Three Generations: Possible hints from neutrinos in elucidating the matter/antimatter asymmetry of the Universe
Despite being one of the most abundant constituents of the Universe and more than a half a century of study, some of the most fundamental properties of the neutrino have only been recently uncovered, and others still remain unresolved. I will discuss important developments in the phenomenon of neutrino oscillations, a transmutation process that allows neutrinos to change between three types as they propagate in time. In particular, recent discoveries have opened up the possibility of CP violation in neutrino oscillations, asymmetries in the behavior of neutrinos and their anti-matter counterparts. CP violation, along with other unresolved properties of the neutrino, may play a central role in how the universe came to a matter-dominated state. I will also discuss a new generation of experiments that may allow us to establish whether CP violation does indeed occur in neutrino oscillations. -
From dlogs to dilogs
Arthur Lipstein Durham University
In this talk, I will describe a new form of hidden simplicity in the planar scattering amplitudes of N=4 super-Yang-Mills theory, notably that the loop integrands can be expressed in dlog form. I will explain how this form arises geometrically from computing the scattering amplitudes using a holomorphic Wilson loop in twistor space. I will also describe a systematic method for evaluating such integrals and use it to obtain a new formula for the 1-loop MHV amplitude. These techniques can be extended to higher loop amplitudes and may lead to a simple and efficient method for computing scattering amplitudes more generally. -
The local Callan-Symanzik equation: structure and applications
Boaz Keren-Zur L'Ecole Polytechnique Federale de Lausanne (EPFL)
The local Callan-Symanzik equation describes the response of a quantum field theory to local scale transformations in the presence of background sources. The consistency conditions associated with this anomalous equation can be used to derive powerful constraints on RG flows. We will discuss various aspects of the equation and present new results regarding the structure of the anomaly. We then use the equation to write correlation functions of the trace of the energy-momentum tensor off-criticality. -
Bottom-up Naturalness
Sonia El Hedri Stanford University
We study the naturalness problem using a model independent bottom up approach by considering models where only the interaction terms needed to cancel the Higgs quadratic divergences are present. If quadratic divergences are canceled by terms linear in the Higgs field, then the collider phenomenology is well covered by current electroweakino and fourth generation searches. If quadratic divergences are canceled by terms bilinear in the Higgs field, then the signatures are highly dependent on the quantum numbers of the new particles. Precision Higgs measurements can reveal the presence of new particles with either vevs or Standard Model charges. If the new particles are scalar dark matter candidates, their direct and indirect detection signatures will be highly correlated and within the reach of XENON100 and Fermi. Observation at one of these experiments would imply observation at the other one. Observable LHC decay channels can also arise if the new particles mix with lighter states. This decay channel involves only the Higgs boson and not the gauge bosons. Observation of such decays would give evidence that the new particle is tied to the naturalness problem. -
Orbifold partition function and their phases
Daisuke Yokoyama Seoul National University
We discuss a partition function of 3d supersymmetric gauge theories on the (p, -1) Lens space.
In 3d the partition function is directly used to check dualities though the normalization is not seriously treated, especially, the phase is usually ignored. However, when we consider the partition function on the orbifold the partition function consists of the sum of factors labeled by holonomies and their relative phases become crucial. We stress that the known formula for the partition function is incorrect and some relative phase factors are needed to identify the partition functions of dual theories. -
Soft and Coulomb resummation: squark and gluino production at the LHC
We consider the production of strongly interacting, heavy SUSY pairs at the LHC. When the centre of mass energy is close to the production threshold of the pair, the corresponding cross sections receive large higher-loop QCD corrections. These corrections are classified as the so-called soft logarithms and Coulomb singularities and they lead to a break down of the usual perturbation expansion. In this talk I review the origin of these large corrections and explain how they can be resummed by using Effective Field theories. Finally, I will present some resummed results for the pair production cross sections of heavy squarks and gluinos. Based on: arXiv:1202.2260 and 1211.3408. -
Fundamental Physics with Optically Levitated Dielectric Objects
Asimina Arvanitaki Perimeter Institute
In the past few years, optical cooling and manipulating of macroscopic objects, such as micro-mirrors and cantilevers has developed into an active field of research. In mechanical systems, the oscillator is attached to its suspension, a thermal contact that limits the motion isolation. On the other hand, when these small objects are levitated using the radiation pressure force of lasers, the excellent thermal isolation even at room temperatures helps produce very sensitive force detectors, and eventually quantum transducers for quantum computation purposes. These new techniques may have a variety of applications for fundamental physics such as short distance tests of gravity and gravitational wave detection at high frequencies. In addition, there are several proposals suggesting that optically levitated dielectrics can be cooled to the ground state of the center of mass motion,
opening the exciting possibility of creating macroscopic matter-wave interferometers. -
Hexagon functions and six-gluon scattering in planar N=4 super-Yang-Mills
Lance Dixon Stanford University
Hexagon functions are a class of iterated integrals, depending on three variables (dual conformal cross ratios) which have the correct branch cut structure and other properties to describe the scattering of six gluons in planar N=4 super-Yang-Mills theory. We classify all hexagon
functions through transcendental weight five, using the coproduct for their Hopf algebra iteratively, which amounts to a set of first-order differential equations. As an example, the three-loop remainder function is a particular weight-six hexagon function, whose symbol was determined
previously.
The differential equations can be integrated numerically for generic values of the cross ratios, or analytically in certain kinematics limits, including the near-collinear and multi-Regge
limits. These limits allow us to impose constraints from the operator product expansion and multi-Regge factorization directly at the function level, and thereby to fix uniquely a set of Riemann-Zeta-valued constants that could not be fixed at the level of the symbol. The near-collinear limits agree precisely with recent predictions by Basso, Sever and Vieira based on integrability. The multi-Regge limits agree with a factorization formula of Fadin and Lipatov, and determine three constants entering the impact factor at this order. We plot the three-loop remainder function for various slices of the Euclidean region of positive cross ratios, and compare it to the two-loop one. For large ranges of the cross ratios, the ratio of the three-loop to the two-loop remainder function is relatively constant, and close to -7.