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.

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

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 present a simple cryostat purpose built for use with surface-electrode ion traps, designed around an affordable, large cooling power commercial pulse tube refrigerator. A modular vacuum enclosure with a single vacuum space facilitates interior access and enables rapid turnaround and flexibility for future modifications. Long rectangular windows provide nearly 360 degrees of optical access in the plane of the ion trap, while a circular bottom window near the trap enables NA 0.4 light collection without the need for in-vacuum optics. We evaluate the system's mechanical and thermal characteristics and we quantify ion trapping performance by trapping 40Ca+, finding small stray electric fields, long ion lifetimes, and low ion heating rates.

Abstract

In heteroepitaxy, lattice mismatch between the deposited material and the underlying surface strongly affects nucleation and growth processes. The effect of mismatch is well studied in atoms with growth kinetics typically dominated by bond formation with interaction lengths on the order of one lattice spacing. In contrast, less is understood about how mismatch affects crystallization of larger particles, such as globular proteins and nanoparticles, where interparticle interaction energies are often comparable to thermal fluctuations and are short ranged, extending only a fraction of the particle size. Here, using colloidal experiments and simulations, we find particles with short-range attractive interactions form crystals on isotropically strained lattices with spacings significantly larger than the interaction length scale. By measuring the free-energy cost of dimer formation on monolayers of increasing uniaxial strain, we show the underlying mismatched substrate mediates an entropy-driven attractive interaction extending well beyond the interaction length scale. Remarkably, because this interaction arises from thermal fluctuations, lowering temperature causes such substrate- mediated attractive crystals to dissolve. Such counterintuitive results underscore the crucial role of entropy in heteroepitaxy in this technologically important regime. Ultimately, this entropic component of lattice mismatched crystal growth could be used to develop unique methods for heterogeneous nucleation and growth of single crystals for applications ranging from protein crystallization to controlling the assembly of nanoparticles into ordered, functional superstructures. In particular, the construction of substrates with spatially modulated strain profiles would exploit this effect to direct self-assembly, whereby nucleation sites and resulting crystal morphology can be controlled directly through modifications of the substrate.

Abstract

A definition of quantum singularity for the case of static spacetimes has has recently been extended to conformally static spacetimes. Here the theory behind quantum singularities in conformally static spacetimes is reviewed and then applied to a class of spherically symmetric, conformally static spacetimes, including as special cases those studied by Roberts, by Fonarev, and by Husain et al. We use solutions of the generally coupled, massless Klein-Gordon equation as test fields. In this way we find the ranges of metric parameters and coupling coefficients for which classical timelike singularities in these spacetimes are healed quantum mechanically.

Recent Publications

Student authorFaculty author

41.

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.
42.

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.
43.

Brian Shuve and Itay Yavin

Dark Matter Progenitor: Light Vector Boson Decay into Sterile Neutrinos

Physical Review D 89 (2014) 113004.
PDF document
Eye candy
44.

Eder Izaguirre, Gordan Krnjaic, and Brian Shuve

Bottom-up Approach to the Galactic Center Excess

Physical Review D 90 (2014) 18.
PDF document
Eye candy
45.

Brian Shuve and Itay Yavin

Baryogenesis Through Neutrino Oscillations: a Unified Perspective

Physical Review D 89 (2014) 32.
PDF document
Eye candy
46.

Jason Gallicchio and Matthew D Schwartz

Quark and gluon jet substructure

Journal of High Energy Physics 2013 (2013) .
47.

Yang Bai, Hsin-Chia Cheng, Jason Gallicchio, and Jiayin Gu

A toolkit of the stop search via the chargino decay

Journal of High Energy Physics 2013 (2013) .
48.

G. Vittorini, K. Wright, K. R. Brown, A. W. Harter, and Charlie Doret

Modular cryostat for ion trapping with surface-electrode ion traps

Review of Scientific Instruments 84 (2013) 043112.
PDF document
2013/Doret_RSI_84_043112
49.

John R. Savage, Stefan F. Hopp, Rajesh Ganapathy, Sharon Gerbode, Andreas Heuer, and I. Cohen

Entropy-Driven Crystal Formation on Highly Strained Substrates

Proceedings of the National Academy of Sciences 110 (2013) 9301-9304.
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50.

Thomas Helliwell and D. A. Konkowski

Quantum singularities in spherically symmetric, conformally static spacetimes

Physical Review D 87 (2013) 104041.