Generic construction of the Standard Model gauge group and matter representations in F-theory

We describe general classes of 6D and 4D F-theory models with gauge group $(\operatorname{SU}(3) \times \operatorname{SU}(2) \times \operatorname{U}(1)) / \mathbb{Z}_6$. We prove that this set of constructions gives all possible consistent 6D supergravity theories with no tensor multiplets having this gauge group and the corresponding generic matter representations, which include those of the MSSM. We expect, though do not prove, that these models are similarly generic for 6D theories with tensor multiplets and for 4D $\mathcal{N} = 1$ supergravity theories. The largest class of these constructions comes from deforming an underlying geometry with gauge symmetry $\operatorname{SU}(4) \times \operatorname{SU}(3) \times \operatorname{SU}(2)$.Comment: 10 pages, LaTeX; references added, minor edit

Geophysics

Contains reports on three research projects

Geophysics

Contains reports on four research projects

Geophysics

Contains reports on three research projects

Geophysics

Contains reports on four research projects.United States Air Force (Contract AF19(628)-500)Lincoln Laboratory (Purchase Order DDL BB-107

Modulator noise suppression in the LISA Time-Delay Interferometric combinations

We previously showed how the measurements of some eighteen time series of relative frequency or phase shifts could be combined (1) to cancel the phase noise of the lasers, (2) to cancel the Doppler fluctuations due to non-inertial motions of the six optical benches, and (3) to remove the phase noise of the onboard reference oscillators required to track the photodetector fringes, all the while preserving signals from passinggravitational waves. Here we analyze the effect of the additional noise due to the optical modulators used for removing the phase fluctuations of the onboard reference oscillators. We use a recently measured noise spectrum of an individual modulator to quantify the contribution of modulator noise to the first and second-generation Time-Delay Interferometric (TDI) combinations as a function of the modulation frequency. We show that modulator noise can be made smaller than the expected proof-mass acceleration and optical-path noises if the modulation frequencies are larger than $\approx 682$ MHz in the case of the unequal-arm Michelson TDI combination $X_1$, $\approx 1.08$ GHz for the Sagnac TDI combination $\alpha_1$, and $\approx 706$ MHz for the symmetrical Sagnac TDI combination $\zeta_1$. These modulation frequencies are substantially smaller than previously estimated and may lead to less stringent requirements on the LISA's oscillator noise calibration subsystem.Comment: 17 pages, 5 figures. Submitted to: Phys. Rev. D 1

Molecular Dynamics Simulation Study of Nonconcatenated Ring Polymers in a Melt: I. Statics

Molecular dynamics simulations were conducted to investigate the structural properties of melts of nonconcatenated ring polymers and compared to melts of linear polymers. The longest rings were composed of N=1600 monomers per chain which corresponds to roughly 57 entanglement lengths for comparable linear polymers. For the rings, the radius of gyration squared was found to scale as N to the 4/5 power for an intermediate regime and N to the 2/3 power for the larger rings indicating an overall conformation of a crumpled globule. However, almost all beads of the rings are "surface beads" interacting with beads of other rings, a result also in agreement with a primitive path analysis performed in the following paper (DOI: 10.1063/1.3587138). Details of the internal conformational properties of the ring and linear polymers as well as their packing are analyzed and compared to current theoretical models.Comment: 15 pages, 14 figure