Speaker: Yasunori Nomura, UC Berkeley
Title: "The Multiverse---Particle Physics, Cosmology, and Quantum Gravity"
Speaker: Peter Boyle, University of Edinburgh
Title: “Precision physics from Lattice QCD”
Abstract:
The increasing precision of Lattice QCD enables the contribution the
best theoretical input for a number constraints on CKM physics. I
discuss in particular the Kl3 semileptonic form factor and the standard
model and beyond standard model Kaon bag parameters. Precise Lattice QCD
simulations are the result of improved theoretical approaches for
renormalisation of lattice operators, state of the art numerical
algorithms and powerful computers. I discuss recent advances in each of
these areas
Speaker: Yuri Kovchegov, The Ohio State University
Title: “Saturation Physics and Rapidity Correlations”
Abstract:
We will present an overview of the recent progress in our understanding of strong interactions in high energy scattering. We will demonstrate how in high energy scattering the wave functions of hadrons and nuclei are densely packed with gluons and quarks leading to a new phenomenon of parton saturation. The transition to the saturation regime is described by the saturation scale, which has a dimension of momentum and can be large in high energy scattering, making the strong coupling small, and allowing for a universal perturbative description of a host of hadronic and nuclear scattering processes. In particular we will discuss the prediction of the saturation physics for di-hadron correlations in high energy collisions. We show that multi-parton interactions inherent in the saturation approach lead to long-range rapidity correlations between the hadrons which have identical near- and away-side "ridge" structure. We compare this prediction to the recent data from the p+Pb run at the LHC.
Speaker: Frederik Denef, Institute for Theoretical Physics, K.U.Leuven
Title: "Controlling quantum cosmology"
Abstract:
Holographic dualities have allowed the construction of UV complete, nonperturbative models of quantum gravity in spacetimes with negative cosmological constant. In contrast, despite suggestive formal similarities, very little progress along these lines has been made for their positive cosmological constant counterparts, or more generally in the construction of complete models of quantum gravity in an expanding universe. I will review some of the attempts of the past, what the obstacles are to the construction of holographic duals, and how the first explicit, recent proposal for such a dual --- the Sp(N) model of Anninos, Hartman and Strominger, conjectured to be dual to 4d higher spin gravity with positive cosmological constant --- manages to circumvent these issues. I will then describe our recent and ongoing work exploring whether this model indeed makes sense beyond perturbation theory, more precisely in its interpretation as providing an exact expression for the "wave function of the (Vasiliev) universe". At this point the evidence is mixed but intriguing. I will also outline a related line of work, addressing the question how the characteristic "evolutionary tree" of macroscopically distinct geometries generated by quantum fluctuations and inflation can be extracted from the late time wave function. Inspired by ideas developed in the theory of spin glasses, we propose to consider certain distance distributions on state space.
Speaker: Sergei Dubovsky, New York University
Title: "Evidence for a new particle on the worldsheet of the QCD flux tube"
Abstract:
We propose a new approach for the calculation of the spectrum of
excitations of QCD flux tubes. It relies on the fact that the worldsheet
theory is integrable at low energies. With this approach, energy levels
can be calculated for much shorter flux tubes than was previously
possible, allowing for a quantitative comparison with existing lattice
data. The improved theoretical control makes it manifest that existing
lattice data provides strong evidence for a new pseudoscalar particle
localized on the QCD fluxtube - the worldsheet axion.
Speaker: Piljin Yi, Korean Institute for Advanced Studies (KIAS)
Title: "Constructive Wall-Crossing & Seiberg-Witten"
Abstract:
In string theory, geometry and quantum states are sometimes tightly connected. The wall-crossing problem is one example, where (non-)existence of so-called calibrated cycles can be figured out by solving relatively simple class of Schroedinger problems, or vice versa.
We start with a one-slide review of the Kontsevich-Soibelman (KS)
solution to the mathematical side of the wall-crossing problem and then
proceed to direct and comprehensive physics counting of BPS states in
the context of Seiberg-Witten theory. We point out several subtleties,
missed by previous such attempts, and provide a universal index formulae
from the semiclassical soliton viewpoint. Newly illuminated are how
field theory index, called protected spin character, is related to the
equivariant index of the low energy quantum mechanics of such BPS
states, and also the origin of rational invariant from quantum Bose and
Fermi statistics of identical particles. In the end, this physical and
constructive approach can be shown to be equivalent to the proposed KS
solution.
Speaker: Rachel Rosen, Columbia University
Title: "Massive Gravity and Beyond: A Particle Physics Approach to Modified Gravity"
Abstract:
The discovery of General Relativity (GR) required a leap of insight, from the equivalence principle and general coordinate invariance to a fully non-linear theory governing the dynamics of spacetime. Yet remarkably, by applying the tenets of relativistic quantum field theory to gravity one can arrive systematically at the same theory of GR. In this talk I will review this approach to gravity. I will show how this same approach can also be used to develop consistent non-linear modifications of GR in which the graviton has a small mass, as well as consistent theories of multiple interacting spin-2 fields. These theories improve our understanding of the interplay between gravity and particle physics and provide new approaches to solving the cosmological constant problem.
Speaker: Xu Feng, High Energy Accelerator Research Organization (KEK)
Title: "The neutral pion decay and the chiral anomaly on the lattice"
Abstract:
We perform a nonperturbative calculation of the pion-to-two-photon
transition form factor and the associated decay width using lattice QCD.
The amplitude for a two-photon final state, which is not an eigenstate
of QCD, is extracted through a Euclidean time integral of the relevant
three-point function. We utilize the all-to-all quark propagator
technique to carry out this integration. We execute the calculation
using the overlap fermion formulation, which ensures the exact chiral
symmetry on the lattice and produces the chiral anomaly through the
Jacobian of the chiral transformation. We calculate the form factor and
decay width with a comprehensive estimate of various systematic errors,
except for a possible discretization effect. Our results reproduce the
predication of the ABJ anomaly in the chiral limit and also agree with
the PrimEx experimental measurement at the physical pion mass.
Title: "Model Independent Direct Detection"
Abstract:
I will describe a model-independent approach to parameterizing possible dark-matter (DM) interactions with nucleons. The idea is to require only terms consistent with Galilean invariance and the rules of quantum mechanics. This general framework leads to novel ways with which nuclei can interact with the DM.
Speaker: Rajan Gupta, Los Alamos National Lab
Title: "Exploring TeV scale physics in decays of [ultra]cold neutrons”
Abstract:
Possible novel scalar and tensor interactions at the TeV scale lead to observable consequences in the decay distribution of neutrons. Such high precision experiments complement direct searches at the LHC. The biggest uncertainty in interpreting current proposed experiments and bounding the scale of these new interactions is the calculation of the scalar and tensor charges of the nucleon. This talk will motivate the physics and describe the status of lattice QCD calculations being done to calculate these charges with the desired precision.
Speaker: Christopher Kelly, Columbia University
Abstract:
The direct violation of the CP symmetry, an essential component for describing the asymmetry between matter and antimatter in the universe, was first observed in the late 1990s in the decays of a kaon into two pions. Since that time the experimental measure of CP violation in this channel has become quite precise. However until recently it has not been possible to calculate this quantity directly from the Standard Model as it receives large contributions from QCD in the hadronic regime in which perturbative calculations are not possible. This is unfortunate because these decays are highly sensitive to Beyond the Standard Model sources of CP violation, and a comparison between the Standard Model prediction and the measured value could potentially lead to the discovery of new physics. Now, using lattice QCD, and combining decades of theoretical and computational developments, such a calculation has become feasible.
The RBC & UKQCD collaboration have recently published the first calculation of the K->pi pi decay amplitude in the I=2 channel. I will discuss the techniques used for this calculation and then describe our progress towards the more difficult task of measuring the decay in the I=0 channel, which represents the last hurdle before a full ab initio value for the measure of CP-violation can be obtained.
Speaker: Philip Schuster, Perimeter Institute
Title: "(Why) Is Helicity Lorentz-Invariant? Part 1: Introduction"
Abstract:
Massless particle states carry integer or half-integer spin about the momentum axis, or "helicity". Lorentz symmetry allows for helicity states to mix under boosts (like massive particle polarizations); such mixing is not understood theoretically and is not obviously well constrained by experiment. This possibility is historically known as "continuous spin" and this talk provides an informal introduction to the subject. We present evidence that "continuous spin" particles (CSPs) can interact with matter via scattering amplitudes that approach familiar scalar, electromagnetic, or gravitational ones in a high energy (and/or non-relativistic) correspondence limit. Such interactions also appear thermodynamically safe.
This talk will focus on the motivation for CSPs, their kinematics, and
properties of consistent amplitudes. We close by identifying some
directions for discovering a full interacting theory of CSPs or proving
that such theories can't exist. A 2nd talk on Tuesday will elaborate
on CSP thermodynamics and on a field theory description of CSPs.
Speaker: Natalia Toro, Perimeter Institute
Title: "(Why) Is Helicity Lorentz-Invariant? Part 2: Thermodynamics and Field Theory"
Abstract:
Massless particle states of integer or half-integer "helicity" can, in general, mix under Lorentz boosts (like massive particle polarizations). This possibility, historically known as "continuous spin" particles (CSPs), is neither well understood theoretically nor obviously well constrained by experiment. This talk is a continuation of the introduction to CSPs given in Part 1 on Monday. We will examine the physical consequences of the "helicity correspondence" in which simple CSP amplitudes approach scalar, electromagnetic, or gravitational amplitudes in a high-energy limit. In particular, we elaborate on the thermodynamics of matter coupled to CSPs at high temperatures and related observational constraints. We also present a gauge field theory description of CSPs, and comment on some puzzles regarding how this theory is related to the scattering amplitudes discussed previously.
Speaker: Raman Sundrum, University of Maryland
Title: "Metaphor for Dark Energy"
Abstract:
At the beginning of the twentieth century, there arose two distinct means of extending Newton's Law of Gravity and the Equivalence Principle to the relativistic regime. Of course one was General Relativity. The other was Nordstrom's theory of scalar gravity, improved further by Einstein and Fokker as a theory of curved spacetime. This theory ultimately failed observational tests of relativistic gravity, but it has come up in other guises in theoretical physics over the decades. I will describe this remarkable theory and update it into the era of quantum mechanics and string theory, and point out that it can provide a simpler "laboratory" for thinking through some tough puzzles of real gravity. In particular I show that scalar gravity has a strikingly faithful version of the cosmological constant problem, satisfying the same no-go "theorems" of real gravity, and yet there is an elegant solution in terms of a subtle form of evolving "dark energy" that can be understood in standard quantum field theory.
Speaker: Jeremy Sakstein, University of Cambridge
Title: "Detecting Modified Gravity in the Stars"
Abstract:
Screened Scalar-Tensor gravity such as chameleon and symmetron theories allow order one deviations from General Relativity on large scales whilst satisfying all local solar-system constraints. A lot of recent work has therefore focused on searching for observational signatures of these models and constraining them. If these models are to be viable then our own solar system is necessarily screened, however, this may not be the case for stars in Dwarf Galaxies, which can exhibit novel and unique phenomena. These new effects can be exploited to produce constraints that are far more competitive than laboratory and cosmological tests and in this talk, I will describe some recent and ongoing work using these phenomena to place new constraints.
* Please visit the Theory Seminar site for updates to the schedule.