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.


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.


We probe the viscous relaxation of structured liquid droplets in the partial wetting regime using a diblock copolymer system. The relaxation time of the droplets is measured after a step change in temperature as a function of three tunable parameters: droplet size, equilibrium contact angle, and the viscosity of the fluid. Contrary to what is typically observed, the late-stage relaxation time does not scale with the radius of the droplet-rather, relaxation scales with the radius squared. Thus, the energy dissipation depends on the contact area of the droplet, rather than the contact line.


We report on the design, construction, and characterisation of a new class of in-vacuo optical levitation trap optimised for use in high-intensity, high-energy laser interaction experiments. The system uses a focused, vertically propagating continuous wave laser beam to capture and manipulate micro-targets by photon momentum transfer at much longer working distances than commonly used by optical tweezer systems. A high speed (10 kHz) optical imaging and signal acquisition system was implemented for tracking the levitated droplets position and dynamic behaviour under atmospheric and vacuum conditions, with ±5 μm spatial resolution. Optical trapping of 10 ± 4 μm oil droplets in vacuum was demonstrated, over timescales of >1 h at extended distances of ~40 mm from the final focusing optic. The stability of the levitated droplet was such that it would stay in alignment with a ~7 μm irradiating beam focal spot for up to 5 min without the need for re-adjustment. The performance of the trap was assessed in a series of high-intensity (\(10^{17}\) W cm) laser experiments that measured the X-ray source size and inferred free-electron temperature of a single isolated droplet target, along with a measurement of the emitted radio-frequency pulse. These initial tests demonstrated the use of optically levitated microdroplets as a robust target platform for further high-intensity laser interaction and pointsourcestudies.


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.


We report on how the relaxation of patterns prepared on a thin film can be controlled by manipulating the symmetry of the initial shape. The validity of a lubrication theory for the capillary-driven relaxation of surface profiles is verified by atomic force microscopy measurements, performed on films that were patterned using focused laser spike annealing. In particular, we observe that the shape of the surface profile at late times is entirely determined by the initial symmetry of the perturbation, in agreement with the theory. The results have relevance in the dynamical control of topographic perturbations for nanolithography and high density memory storage.


We investigate the dewetting of a disordered melt of diblock copolymer from an ordered residual wetting layer. In contrast to simple liquids where the wetting layer has a fixed thickness and the droplets exhibit a single unique contact angle with the substrate, we find that structured liquids of diblock copolymer exhibit a discrete series of wetting layer thicknesses each producing a different contact angle. These quantized contact angles arise because the substrate and air surfaces each induce a gradient of lamellar order in the wetting layer. The interaction between the two surface profiles creates an effective interface potential that oscillates with film thickness, thus, producing a sequence of local minimums. The wetting layer thicknesses and corresponding contact angles are a direct measure of the positions and depths of these minimums Self-consistent field theory is shown to provide qualitative agreement with the experiment.


Baryogenesis through neutrino oscillations is an elegant mechanism that has found several realizations in the literature corresponding to different parts of the model parameter space. Its appeal stems from its minimality and dependence only on physics below the weak scale. In this paper we show that by focusing on the physical time scales of leptogenesis instead of the model parameters, a more comprehensive picture emerges. The different regimes previously identified can be understood as different relative orderings of these time scales. This approach also shows that all regimes require a coincidence of time scales and this in turn translates to a certain tuning of the parameters, whether in mass terms or Yukawa couplings. Indeed, we show that the amount of tuning involved in the minimal model is never less than one part in 105 according to a metric constructed from a combination of the sterile neutrino mass degeneracy and the Barbieri-Giudice tuning of the Yukawa coupling. Finally, we explore an extended model, where the tuning can be removed in exchange for the introduction of a new degree of freedom in the form of a leptophilic Higgs with a vacuum expectation value of the order of GeV.

Recent Publications

Student authorFaculty author


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) .
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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.
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Mark Ilton, Oliver Baeumchen, and Kari Dalnoki-Veress

Onset of Area-Dependent Dissipation in Droplet Spreading

Physical Review Letters 115 (2015) .

C. J. Price, Thomas D. Donnelly, S. Giltrap, N. H. Stuart, S. Parker, S. Patankar, H. F. Lowe, D. Drew, E. T. Gumbrell, and R. A. Smith

An in-vacuo optical levitation trap for high-intensity laser interaction experiments with isolated microtargets

Review of Scientific Instruments 86 (2015) 033502.
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RSI Donnelly 2015

Eder Izaguirre and Brian Shuve

Multilepton and Lepton Jet Probes of Sub-Weak-Scale Right-Handed Neutrinos

Physical Review D 91 (2015) 093010.
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Michael Benzaquen, Mark Ilton, Michael V. Massa, Thomas Salez, Paul Fowler, Elie Raphael, and Kari Dalnoki-Veress

Symmetry plays a key role in the erasing of patterned surface features

Applied Physics Letters 107 (2015) .

Mark Ilton, Pawel Stasiak, Mark W. Matsen, and Kari Dalnoki-Veress

Quantized Contact Angles in the Dewetting of a Structured Liquid

Physical Review Letters 112 (2014) 068303.
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Brian Shuve and Itay Yavin

Baryogenesis Through Neutrino Oscillations: a Unified Perspective

Physical Review D 89 (2014) 32.
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Luke St. Marie, Fangzhao Alex An, Anthony L. Corso, John T. Grasel, and Richard C. Haskell

Robust, Real-time, Digital Focusing for FD-OCM using ISAM on a GPU

Optical Coherence Tomography and Coherence Domain Optical Methods in Biomedicine XVIII 8934 (2014) 89342V.