### Abstract

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.

### Abstract

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.

### Abstract

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.

### Abstract

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.

### Abstract

We propose a practical scheme to use photons from causally disconnected cosmic sources to set the detectors in an experimental test of Bells inequality. In current experiments, with settings determined by quantum random number generators, only a small amount of correlation between detector settings and local hidden variables, established less than a millisecond before each experiment, would suffice to mimic the predictions of quantum mechanics. By setting the detectors using pairs of quasars or patches of the cosmic microwave background, observed violations of Bells inequality would require any such coordination to have existed for billions of yearsan improvement of 20 orders of magnitude.

### Abstract

It has recently been shown that dark-matter annihilation to bottom quarks provides a good fit to the Galactic Center gamma-ray excess identified in the Fermi-LAT data. In the favored dark-matter mass range $$m \sim$$ 30–40 GeV, achieving the best-fit annihilation rate $$\sigma v \sim 5 \times 10^{-26} \, \mathrm{cm^3 s^{-1}}$$ with perturbative couplings requires a sub-TeV mediator particle that interacts with both dark matter and bottom quarks. In this paper, we consider the minimal viable scenarios in which a Standard Model singlet mediates s-channel interactions only between dark matter and bottom quarks, focusing on axial-vector, vector, and pseudoscalar couplings. Using simulations that include on-shell mediator production, we show that existing sbottom searches currently offer the strongest sensitivity over a large region of the favored parameter space explaining the gamma-ray excess, particularly for axial-vector interactions. The 13 TeV LHC will be even more sensitive; however, it may not be sufficient to fully cover the favored parameter space, and the pseudoscalar scenario will remain unconstrained by these searches. We also find that direct- detection constraints, induced through loops of bottom quarks, complement collider bounds to disfavor the vector-current interaction when the mediator is heavier than twice the dark-matter mass. We also present some simple models that generate pseudoscalar-mediated annihilation predominantly to bottom quarks.

### Abstract

We show that the existence of new, light gauge interactions coupled to Standard Model (SM) neutrinos gives rise to an abundance of sterile neutrinos through the sterile neutrinos’ mixing with the SM. Specifically, in the mass range of MeV–GeV and coupling of $$g' \sim 10^{-6}$$–$$10^{-3}$$, the decay of this new vector boson in the early Universe produces a sufficient quantity of sterile neutrinos to account for the observed dark matter abundance. Interestingly, this can be achieved within a natural extension of the SM gauge group, such as a gauged $$L_{\mu}$$ − $$L_{\tau}$$ number, without any tree-level coupling between the new vector boson and the sterile neutrino states. Such new leptonic interactions might also be at the origin of the well-known discrepancy associated with the anomalous magnetic moment of the muon.

# Recent Publications

Student authorFaculty author

31. 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) . 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. 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. Alanna L. Weisberg, Nathaniel J. Bean, Theodore B. DuBose, Elizabeth Orwin, and Richard C. Haskell Physical Attributes and Assembly of PEG-linked Immuno-labeled Gold Nanoparticles for OCM Image Contrast in Tissue Engineering and Developmental Biology Optical Coherence Tomography and Coherence Domain Optical Methods in Biomedicine XVIII 8934 (2014) 89342V. Brian Shuve and Itay Yavin Baryogenesis Through Neutrino Oscillations: a Unified Perspective Physical Review D 89 (2014) 32. 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. Jason Gallicchio, Andrew S. Friedman, and David I. Kaiser Testing Bell’s Inequality with Cosmic Photons: Closing the Setting-Independence Loophole Physical Review Letters 112 (2014) 195. Eder Izaguirre, Gordan Krnjaic, and Brian Shuve Bottom-up Approach to the Galactic Center Excess Physical Review D 90 (2014) 18. Brian Shuve and Itay Yavin Dark Matter Progenitor: Light Vector Boson Decay into Sterile Neutrinos Physical Review D 89 (2014) 113004. Jason Gallicchio and Matthew D Schwartz Quark and gluon jet substructure Journal of High Energy Physics 2013 (2013) .