Scientific Series

Energy and momentum are conserved in Newton's laws of gravitation.
Numerical integration of the equations of motion should comply to
these requirements in order to guarantee the correctness of a
solution, but this turns out to be insufficient.  The steady growth of
numerical errors and the exponential divergence, renders numerical
solutions over more than a dynamical time-scale meaningless.  Even
time reversibility is not a guarantee for finding the definitive
solution to the numerical few-body problem.  As a consequence,
numerical N-body simulations produce questionable results.  Using
brute force integrations to arbitrary numerical precision I will
demonstrate empirically that the statistics of an ensemble of resonant
3-body interactions is independent of the precision of the numerical
integration, and conclude that, although individual solutions using
common integration methods are unreliable, an ensemble of approximate
3-body solutions accurately represent the ensemble of true solutions.

Part 1 is about anomalies and how they can deform generalized global symmetry into 2-group global symmetry.  This is illustrated with simple QFT examples in 4d.  Part 2 is about 6d.

6d theories with 2-group symmetry exist, but cannot be conformal.  6d superconformal theories (SCFTs) cannot have 2-group or higher-form, generalized global symmetries.  This requires cancellation of mixed gauge and global terms in the anomaly polynomial.   SCFT relations between conformal and ’t Hooft anomalies will also be discussed.   Based on papers with Cordova and Dumitrescu.

New scalar bosons that are uncharged under the Standard Model have many phenomenological applications, and in particular may serve as mediators between the dark and visible sectors. Such scalars are often taken to have Higgs-like couplings to Standard Model fermions, in order to evade constraints from bounds on flavor-changing neutral currents.
We describe an alternative approach, based on an effective field theory approach in which a new scalar preferentially couples to a single fermion mass eigenstate. In such theories, we show through a spurion analysis that small flavor changing couplings are still technically natural. Examples of our framework include a muon-philic scalar that can explain the observed anomalous magnetic moment of the muon and an up-specific scalar mediator to a dark sector, whose phenomenologies we discuss in detail.

In this talk I will discuss several aspects of using the 21cm Intensity Mapping (IM) as a Large-Scale Structure (LSS) probe in order to better constrain the cosmological parameters. I will start with a Baryon Acoustic Oscillations (BAO) reconstruction method intended for 21cm IM observations at low redshifts. I will then present the predictions and gains of performing 21cm IM surveys at redshift range which is currently vastly unobserved (2<z<6). Finally I will show the results of using existing data (ALFALFA & SDSS) to place constraints on the distribution of neutral hydrogen (HI) in dark matter halos as a function of the halo mass. This is then used to constrain and improve the HI halo model needed to make accurate and precise predictions on the 21cm signal and the noise.

Bulk coherent states produced by Euclidean CFT sources can be used to study how geometry arises from entanglement: when these states obey the Ryu-Takayanagi formula, the linearized Einstein equations hold in the bulk without assuming the complete AdS/CFT correspondence.  However, the Faulkner-Lewkowycz-Maldacena bulk entanglement term that corrects the RT formula does not play a role in these previous studies, since to leading order coherent states have the same entanglement entropy as the vacuum.  We study states CFT states created by Euclidean, bilocal, double trace sources, which produce bulk squeezed states.  We consider possible modifications to RT and study divergences in the perturbative expansion that occur for certain choices of source.  We work towards determining constraints on the bulk geometry and state that arise from requiring FLM, akin to the linearized Einstein equations that arose for coherent states.

In recent years the Standard Model Effective Field Theory (SMEFT) has emerged as a well defined and systematically improvable theory to study the constraints on physics beyond the Standard Model. This formalism explains old mysteries in interpreting LEP data and offers a field theory framework to combine such data with LHC measurements of the properties of the Higgs. We discuss the current status of these combined studies. The lack of evidence for new physics resonances at LHC has also encouraged new approaches to explaining the observed value of the electroweak scale, in the presence of physics beyond the Standard Model. One such approach is the Neutrino Option, that generates the electroweak scale from an underlying Majorana scale, when Neutrino masses come about due to a seesaw mechanism. We discuss how this approach is embedded into the SMEFT.

As a proxy for a Quantum Gravity theory, String Theory introduces new degrees of freedom and symmetries that should play a major role in the physics of the early universe. We motivate the introduction of these ingredients as we review some of the issues of the inflationary paradigm. Among these new ingredients, T-duality may help us to solve the Big Bang singularity and yield a different cosmological scenario. Thus, we review how this has been thought in the context of Double Field Theory, which aims to build a covariant field theory under T-duality's group, and consider its cosmological applications. 

I will discuss recent developments in the theory of relativistic turbulence, from both pure physics and astronomical perspectives. Turbulence in relativistic fluids and plasmas has applicability in high energy density physics, in early-universe cosmology, and in high energy astrophysics. I will focus on its connections with multi-messenger astrophysics, particularly in the context of binary neutron star (BNS) mergers, and the electromagnetic signals that accompany their gravitational wave emission. My talk will include (1) an overview of methods used to simulate and characterize relativistic turbulence, (2) implications of dynamo theory to the dynamics of BNS mergers, (3) new ideas emerging in the theory of "radiation-mediated" relativistic turbulence, and (4) efforts in modeling the prompt and afterglow emission from GW-170817.

Recent years have shown that error correction is one of the most fundamental ingredients of various physical phenomena, from topological order to holography. However, only toy models and fixed point ground states could have been studied, even though the error-correcting properties are expected to hold generally in the low energy subspace.

In this talk, we will employ Matrix Product State formalism and see how low energy eigenstates of 1D translationally invariant Hamiltonians can form quantum error-correcting codes. Before diving into the results, we will review the necessary basics of quantum error correction and matrix product states.

Joint work with Martina Gschwendtner, Robert Koenig and Eugene Tang.

I give an overview of trapped ion quantum information experiments and discuss prospects for implementing multi-valued quantum logic using trapped ions. Qudits (the multi-state generalization of qubits) are attractive for quantum computing because they enable a much larger Hilbert space for the same number of trapped ions, which may allow us to improve the information capacity of a quantum processor. I describe possible advantages and disadvantages of using qudits in place of qubits, and lay out some of the protocols that my lab will test for implementing measurements, single-qudit operations, and two-qudit operations in a trapped ion system.

Supersymmetry (SUSY) has not been verified so far as a fundamental symmetry in particle physics. Emergent phenomena in condensed matter physics bring the possibility of realizing SUSY as an IR symmetry. We show that 2+1D N=2 Nf=2 supersymmetric quantum electrodynamics (SQED3) with dynamical gauge bosons and fermionic gauginos emerges naturally at the tricritical point of nematic pair-density-wave (PDW) quantum phase transition on the surface of a correlated topological insulator hosting three Dirac cones, such as the topological Kondo insulator SmB6. It provides a first example of emergent supersymmetric gauge theory in condensed matter systems. We also investigate the possibility of emergent 3+1D SUSY theory in lattice models. By constructing an explicit fermionic lattice model featuring two 3D Weyl nodes, we find a continuous PDW quantum phase transition as a function of attractive Hubbard interaction. We further show that N=1 3+1D SUSY emerges at the PDW transition, which we believe is the first realization of emergent 3+1D space-time SUSY in microscopic lattice models. Supersymmetry allows us to determine certain critical exponents and the optical conductivity at the strongly coupled fixed point exactly, which may be measured in future experiments.

In this talk I will discuss generalising the mapping from quantum error correcting codes to stat. mech. models (originally due to Dennis, Kitaev, Landahl and Preskill) to the case of correlated Pauli noise. This mapping connects the error correcting threshold to a phase transition, allowing us to use methods for studying stat. mech. models to estimate code thresholds. Using this, I will present numerical estimates of toric code thresholds under correlated noise. Time permitting, I will also discuss how this mapping can be used to give a tensor network-based algorithm for approximate optimal decoding of 2d topological codes, generalising the decoder of Bravyi, Suchara and Vargo.