### Abstract

The complex antiferromagnetic orders observed in the honeycomb iridates are a double-edged sword in the search for a quantum spin-liquid: both attesting that the magnetic interactions provide many of the necessary ingredients, while simultaneously impeding access. Focus has naturally been drawn to the unusual magnetic orders that hint at the underlying spin correlations. However, the study of any particular broken symmetry state generally provides little clue about the possibility of other nearby ground states. Here we use magnetic fields approaching 100 tesla to reveal the extent of the spin correlations in $$\gamma$$-lithium iridate. We find that a small component of field along the magnetic easy-axis melts long-range order, revealing a bistable, strongly correlated spin state. Far from the usual destruction of antiferromagnetism via spin polarization, the high-field state possesses only a small fraction of the total iridium moment, without evidence for long-range order up to the highest attainable magnetic fields.

### Abstract

Honeycomb iridates such as $\gamma$-Li2IrO3 are argued to realize Kitaev spin-anisotropic magnetic exchange, along with Heisenberg and possibly other couplings. While systems with pure Kitaev interactions are candidates to realize a quantum spin-liquid ground state, in $\gamma$-Li2IrO3 it has been shown that the presence of competing magnetic interactions leads to an incommensurate spiral spin order at ambient pressure below 38 K. We study the pressure sensitivity of this magnetically ordered state in single crystals of $\gamma$-Li2IrO3 using resonant x-ray scattering (RXS) under applied hydrostatic pressures of up to 3 GPa. RXS is a direct probe of electronic order, and we observe the abrupt disappearance of the q sp=(0.57, 0, 0) spiral order at a critical pressure Pc= 1.4 GPa with no accompanying change in the symmetry of the lattice.

### Abstract

Magnetic honeycomb iridates are thought to show strongly spin-anisotropic exchange interactions which, when highly frustrated, lead to an exotic state of matter known as the Kitaev quantum spin liquid. However, in all known examples these materials magnetically order at finite temperatures, the scale of which may imply weak frustration. Here we show that the application of a relatively small magnetic field drives the three-dimensional magnet $$\beta-\mathrm{Li}_2\mathrm{IrO}_3$$ from its incommensurate ground state into a quantum correlated paramagnet. Interestingly, this paramagnetic state admixes a zig-zag spin mode analogous to the zig-zag order seen in other Mott-Kitaev compounds. The rapid onset of the field-induced correlated state implies the exchange interactions are delicately balanced, leading to strong frustration and a near degeneracy of different ground states.

### Abstract

In the context of the Bank-Fishler-Shenker-Susskind Matrix theory, we analyze a spherical membrane in light-cone M theory along with two asymptotically distant probes. In the appropriate energy regime, we find that the membrane behaves like a smeared Matrix black hole; and the spacetime geometry seen by the probes can become non-commutative even far away from regions of Planckian curvature. This arises from nonlinear Matrix interactions where fast matrix modes lift a flat direction in the potential — akin to the Paul trap phenomenon in atomic physics. In the regime where we do have a notion of emergent spacetime, we show that there is non-zero entanglement entropy between supergravity modes on the membrane and the probes. The computation can easily be generalized to other settings, and this can help develop a dictionary between entanglement entropy and local geometry — similar to Ryu-Takayanagi but instead for asymptotically flat backgrounds.

### Abstract

We report on the capillary-driven leveling of a topographical perturbation at the surface of a freestanding liquid nanofilm. The width of a stepped surface profile is found to evolve as the square root of time. The hydrodynamic model is in excellent agreement with the experimental data. In addition to exhibiting an analogy with diffusive processes, this novel system serves as a precise nanoprobe for the rheology of liquids at interfaces in a configuration that avoids substrate effects.

### Abstract

In this paper, we propose a novel powerful strategy to perform searches for new electroweak states. Uncolored electroweak states appear in generic extensions of the Standard Model (SM) and yet are challenging to discover at hadron colliders. This problem is particularly acute when the lightest state in the electroweak multiplet is neutral and all multiplet components are approximately degenerate. In this scenario, production of the charged fields of the multiplet is followed by decay into nearly invisible states; if this decay occurs promptly, the only way to infer the presence of the reaction is through its missing energy signature. Our proposal relies on emission of photon radiation from the new charged states as a means of discriminating the signal from SM backgrounds. We demonstrate its broad applicability by studying two examples: a pure Higgsino doublet and an electroweak quintuplet field.

### Abstract

Dark Matter particles with inelastic interactions are ubiquitous in extensions of the Standard Model, yet remain challenging to fully probe with existing strategies. We propose a series of powerful searches at hadron and lepton colliders that are sensitive to inelastic dark matter dynamics. In representative models featuring either a massive dark photon or a magnetic dipole interaction, we find that the LHC and BABAR could offer strong sensitivity to the thermal relic dark matter parameter space for dark matter masses between ∼100 MeV and 100 GeV and fractional mass-splittings above the percent level; future searches at Belle II with a dedicated monophoton trigger could also offer sensitivity to thermal relic scenarios with masses below a few GeV. Thermal scenarios with either larger masses or splittings are largely ruled out; lower masses remain viable yet may be accessible with other search strategies.

### Abstract

We study pore nucleation in a model membrane system, a freestanding polymer film. Nucleated pores smaller than a critical size close, while pores larger than the critical size grow. Holes of varying size were purposefully prepared in liquid polymer films, and their evolution in time was monitored using optical and atomic force microscopy to extract a critical radius. The critical radius scales linearly with film thickness for a homopolymer film. The results agree with a simple model which takes into account the energy cost due to surface area at the edge of the pore. The energy cost at the edge of the pore is experimentally varied by using a lamellar-forming diblock copolymer membrane. The underlying molecular architecture causes increased frustration at the pore edge resulting in an enhanced cost of pore formation.

### Abstract

We propose new searches that exploit the unique signatures of decaying sterile neutrinos with masses below MW at the LHC, where they can be produced in rare decays of Standard Model gauge bosons. We show that, for few-GeV-scale sterile neutrinos, the LHC experiments can probe mixing angles at the level of $$10^{-4}$$–$$10^{-3}$$ through powerful searches that look for a prompt lepton in association with a displaced lepton jet. For higher-mass sterile neutrinos, i.e., $$M_N \overset{>}{\sim} 15 \, \mathrm{GeV}$$, run II can explore similarly small mixing angles in prompt multilepton final states. This represents an improvement of up to 2 orders of magnitude in sensitivity to the sterile neutrino production rate.

# Recent Publications

Student authorFaculty author

31. K A Modic, B J Ramshaw, J B Betts, Nicholas P. Breznay, James G Analytis, Ross D McDonald, and Arkady Shekhter Robust Spin Correlations at High Magnetic Fields in the Harmonic Honeycomb Iridates Nature Communications 8 (2017) 2. Nicholas P. Breznay, Alejandro Ruiz, Alex Frano, Wenli Bi, Robert J. Birgeneau, Daniel Haskel, and James G. Analytis Resonant X-Ray Scattering Reveals Possible Disappearance of Magnetic Order Under Hydrostatic Pressure in the Kitaev Candidate $\Gamma$-Li$_2$Iro$_3$ Physical Review B 96 (2017) 020402. Alejandro Ruiz, Alex Frano, Nicholas P. Breznay, Itamar Kimchi, Toni Helm, Iain Oswald, Julia Y. Chan, R. J. Birgeneau, Zahirul Islam, and James G. Analytis Correlated States in $$\beta-\mathrm{Li}_2\mathrm{IrO}_3$$ Driven by Applied Magnetic Fields Nature Communications 8 (2017) 961. Vatche Sahakian, Yossathorn Tawabutr, and Xinrui Yan Emergent Spacetime & Quantum Entanglement in Matrix Theory Journal of High Energy Physics 08 (2017) 140. Mark Ilton, Miles M. P. Couchman, Cedric Gerbelot, Michael Benzaquen, Paul D. Fowler, Howard A. Stone, Elie Raphael, Kari Dalnoki-Veress, and Thomas Salez Capillary Leveling of Freestanding Liquid Nanofilms Physical Review Letters 117 (2016) . Brian Shuve and Michael E. Peskin Revision of the LHCb Limit on Majorana Neutrinos Physical Review D 94 (2016) 113007. Ahmed Ismael, Eder Izaguirre, and Brian Shuve Illuminating New Electroweak States at Hadron Colliders Physical Review D 94 (2016) 015001. Eder Izaguirre, Gordan Krnjaic, and Brian Shuve Discovering Inelastic Thermal Relic Dark Matter at Colliders Physical Review D 93 (2016) 063523. Mark Ilton, Christian DiMaria, and Kari Dalnoki-Veress Direct Measurement of the Critical Pore Size in a Model Membrane Physics Review Letters 117 (2016) . Eder Izaguirre and Brian Shuve Multilepton and Lepton Jet Probes of Sub-Weak-Scale Right-Handed Neutrinos Physical Review D 91 (2015) 093010.