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An anomalous measurement of delta m31 squared from neutrino oscillations at the Daya Bay Reactor Neutrino Experiment

Mon, 22 Apr 2013 05:00:00 GMT

Title: An anomalous measurement of delta m31 squared from neutrino oscillations at the Daya Bay Reactor Neutrino Experiment Authors: Burroughs, Hunter Abstract: In 2012, the collaboration overseeing the Daya Bay Reactor Neutrino Experiment announced results which determined the magnitude of the mixing angle \theta_{13} with unprecedented precision. However, no attempt was made in the collaboration’s publications to predict the value of the most relevant mass-squared difference to the observed oscillation, \delta m^2_{31}. This paper presents the results of an analysis which suggests that the Daya Bay data prefers a value of \delta m^2_{31} which is far greater than its presently recognized value. Specifically, it is found that Daya Bay predicts \delta m^2_{31} = 3.53_(-1.07)^(+.74) × 10^(-3) eV^2, where the cited uncertainties correspond to the 99% confidence bounds. This measurement excludes the most precise current measurement of \delta m^2_{31}, the MINOS result, at a 99% confidence level and is in turn excluded by the MINOS data at a 10 \sigma level. The possibility that sterile neutrino effects are the cause of this anomalous result is considered and used to suggest further work.

Simulations of Nano-Structures in Time Dependent External Fields

Mon, 22 Apr 2013 05:00:00 GMT

Title: Simulations of Nano-Structures in Time Dependent External Fields Authors: Atkinson, Mackenzie Abstract: Time Dependent Density Functional Theory is used to probe the structure of matter. Coulomb explosion of small hydrocarbons driven by strong laser pulses and electron holography of molecules are studied in a theoretical framework. The spectra of the ejected protons obtained computationally is in good agreement with experimental data of Coulomb explosion. TDDFT allowed us to obtain time-dependent data, giving us a deeper understanding of the process. Our computational approach to electron holography provides 3-d reconstructions of simple molecules. Further investigation is needed in order to reconstruct larger molecules.

Dark radiation from particle decays during big bang nucleosynthesis

Sun, 01 Apr 2012 05:00:00 GMT

Title: Dark radiation from particle decays during big bang nucleosynthesis Authors: Menestrina, Justin Abstract: Cosmic microwave background (CMB) observations suggest the possibility of an extra dark radiation component, while the current evidence from big bang nucleosynthesis (BBN) is more ambiguous. Dark radiation from a decaying particle can affect these two processes differently. Early decays add an additional radiation component to both the CMB and BBN, while late decays can alter the radiation content seen in the CMB while having a negligible effect on BBN. Here we quantify this difference and explore the intermediate regime by examining particles decaying during BBN, i.e., particle lifetimes τ_X satisfying 0.1 sec < τ_X < 1000 sec. We calculate the change in the effective number of neutrino species, Neff, as measured by the CMB, ΔN_CMB, and the change in the effective number of neutrino species as measured by BBN, ΔN_BBN, as a function of the decaying particle initial energy density and lifetime, where DNBBN is defined in terms of the number of additional two-component neutrinos needed to produce the same change in the primordial 4He abundance as our decaying particle. As expected, for short lifetimes (τ_X < 0.1 sec), the particles decay before the onset of BBN, and DNCMB = DNBBN, while for long lifetimes (τ_X >1000 sec), ΔN_BBN is dominated by the energy density of the nonrelativistic particles before they decay, so that ΔN_BBN remains nonzero and becomes independent of the particle lifetime. By varying both the particle energy density and lifetime, one can obtain any desired combination of N_BBN and ΔN_CMB, subject to the constraint that DNCMB N_BBN. We present limits on the decaying particle parameters derived from observational constraints on ΔN_CMB, and N_BBN.

Real-time real-space density functional theory calculations of electron scattering in materials

Fri, 04 May 2012 05:00:00 GMT

Title: Real-time real-space density functional theory calculations of electron scattering in materials Authors: Wyatt, Benjamin Abstract: Density functional theory is utilized in real-time, real-space simulations of LEED measurements and attosecond electron scattering. For LEED measurements, we find that our simulation results agree well with experimental data and other theoretical approaches. For attosecond electron scattering, we find that the wavefunction of the scattered electron is not signficantly changed by the scattering process, and the measured electron density seems to be related to the initial form of the wave-packet. However, further investigation is needed to confirm these results for different choices of initial form.