Search Talks

Axion-like particles are a broad class of dark matter candidates which are expected to behave as a coherent, classical field with a weak coupling to photons. Research into the detectability of these particles with laser interferometers has recently revealed a number of promising experimental designs. Inspired by these ideas, we propose the Axion Detection with Birefringent Cavities (ADBC) experiment, a new axion interferometry concept using a cavity that exhibits birefringence between its two, linearly-polarized laser eigenmodes. This experimental concept overcomes several limitations of the designs currently in the literature, and can be practically realized in the form of a simple bowtie cavity with tunable mirror angles. Our design thereby increases the sensitivity to the axion-photon coupling over a wide range of axion masses.

Anomaly cancellation conditions place strong constraints on many physical theories. In the traditional framework, local and global anomalies are detected by computing an eta invariant of a certain Dirac operator on a mapping torus. Recent research has uncovered the existence of finer anomaly cancellation conditions, not visible in these traditional settings. I will review the traditional and refined anomalies, and apply them to various symmetries of interest in particle physics. Examples include the (various global forms of) the Standard Model, GUT's, and discrete gauge symmetries of physical interest such as proton triality and a certain Z4 symmetry in the (MS)SM.

The Twin Higgs model is an attractive solution to the little Hierarchy problem with top partners that are neutral under SM gauge charges. The framework is consistent with the null result of LHC colored top partner searches while offering many alternative discovery channels. Depending on model details, the phenomenology looks very different: either spectacular long-lived particle signals at colliders, or a plethora of unusual cosmological and astrophysical signatures via the existence of a predictive hidden sector. I will examine the latter possibility, and describe how the asymmetrically reheated Mirror Twin Higgs provides a predictive framework for a highly motivated and highly non-trivial interacting dark sector, with correlated signals in the CMB, Large Scale Structure, and direct detection searches, as well as higgs precision measurements at colliders. This provides a vivid example of the collider-cosmology complementarity, and motivates a variety of new astrophysical searches that are motivated by the hierarchy problem.

In many-body chaotic systems, the size of an operator generically grows in Heisenberg evolution, which can be measured by certain out-of-time-ordered four-point functions. However, these only provide a coarse probe of the full underlying operator growth structure. We develop a methodology to derive the full growth structure of fermionic systems, that also naturally introduces the effect of finite temperature. We then apply our methodology to the SYK model, which features all-to-all q-body interactions. We derive the full operator growth structure in the large q limit at all temperatures. We see that its temperature dependence has a remarkably simple form consistent with the slowing down of scrambling as temperature is decreased. Furthermore, our finite-temperature scrambling results can be modeled by a modified epidemic model, where the thermal state serves as a vaccinated population, thereby slowing the overall rate of infection.

Motivated by the problem of defining the entanglement entropy of the graviton, we study the division of the phase space of general relativity across subregions. Our key requirement is demanding that the separation into subregions is imaginary---i.e., that entangling surfaces are not physical. This translates into a certain condition on the symplectic form. We find that gravitational subregions that satisfy this condition are bounded by surfaces of extremal area. We characterise the 'centre variables' of the phase space of the graviton in such subsystems, which can be taken to be the conformal class of the induced metric in the boundary, subject to a constraint involving the traceless part of the extrinsic curvature. We argue that this condition works to discard local deformations of the boundary surface to infinitesimally nearby extremal surfaces, that are otherwise available for generic codimension-2 extremal surfaces of dimension ≥ 2.

I will discuss how holographic and effective field theory methods could shed light on important open questions in low energy condensed matter systems. I will focus on the study of the vibrational degrees of freedom, i.e. ''phonons'', in liquids, solids and disordered systems like glasses. Building intuition from the holographic systems I will tackle the problem of the low frequency elastic response in liquids and the universal emergence of the boson peak in ordered crystals and amorphous solids.

Laser spectroscopy of muonic hydrogen [1,2] yielded a proton rms charge radius which is 4% (or ~6 sigmas) smaller than the CODATA value [3]. This discrepancy is now called the "proton radius puzzle" [4].
Also the deuteron charge radius from muonic deuterium [5] is 6 sigmas smaller than the
CODATA value, but consistent with the smaller proton inside the deuteron.
These smaller charge radii, when combined with precision measurements of the 1S-2S transitions in regular (electronic) hydrogen [6] and deuterium [7], yield a 6 sigmas smaller value of the Rydberg constant [8], compared to the CODATA value.
In this talk I will report about a new measurement of the Rydberg constant from the 2S-4P transition in regular hydrogen performed in Garching [9], which supports the smaller, "muonic" value. More recently, however, a new measurement of the 1S-3S transition in Paris confirmed the larger proton radius [10].
Several new measurements, such as hydrogen from Toronto, elastic electron scattering at lower Q², and new results from electronic and muonic helium will help understand the proton radius puzzle.

Hidden sectors are motivated by a range of phenomena unexplained by the Standard Model, such as dark matter, neutrino masses, and the baryon asymmetry. Hidden sector particles below the weak scale can be copiously produced at high-energy and intensity-frontier experiments, but may have evaded detection with current searches.
I will discuss new searches I am doing with the BaBar collaboration that are probing unexplored, well-motivated territory for hidden sectors. I will also show how signatures such as displaced vertices motivate comprehensive, complementary searches at low- and high-energy experiments.

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.

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.