3,007 research outputs found
Field dynamics and tunneling in a flux landscape
We investigate field dynamics and tunneling between metastable minima in a
landscape of Type IIB flux compactifications, utilizing monodromies of the
complex structure moduli space to continuously connect flux vacua. After
describing the generic features of a flux-induced potential for the complex
structure and Type IIB axio-dilaton, we specialize to the Mirror Quintic
Calabi--Yau to obtain an example landscape. Studying the cosmological dynamics
of the complex structure moduli, we find that the potential generically does
not support slow-roll inflation and that in general the landscape separates
neatly into basins of attraction of the various minima. We then discuss
tunneling, with the inclusion of gravitational effects, in many-dimensional
field spaces. A set of constraints on the form of the Euclidean paths through
field space are presented, and then applied to construct approximate instantons
mediating the transition between de Sitter vacua in the flux landscape. We find
that these instantons are generically thick-wall and that the tunneling rate is
suppressed in the large-volume limit. We also consider examples where
supersymmetry is not broken by fluxes, in which case near-BPS thin-wall bubbles
can be constructed. We calculate the bubble wall tension, finding that it
scales like a D- or NS-brane bubble, and comment on the implications of this
correspondence. Finally, we present a brief discussion of eternal inflation in
the flux-landscape.Comment: 23 PRD-style pages with 11 embedded figures. Added refs, corrected
typos, and clarified Sec. V. Replaced to match published versio
Higgs triplets at like-sign linear colliders and neutrino mixing
We study the phenomenology of the type-II seesaw model at a linear e^-e^-
collider. We show that the process e^-e^- \rightarrow alpha^-beta^- (alpha,
beta = e, mu, tau being charged leptons) mediated by a doubly charged scalar is
very sensitive to the neutrino parameters, in particular the absolute neutrino
mass scale and the Majorana CP-violating phases. We identify the regions in
parameter space in which appreciable collider signatures in the channel with
two like-sign muons in the final state are possible. This includes Higgs
triplet masses beyond the reach of the LHC.Comment: 8 pages, 6 figure
Dynamical invariants for quantum control of four-level systems
We present a Lie-algebraic classification and detailed construction of the
dynamical invariants, also known as Lewis-Riesenfeld invariants, of the
four-level systems including two-qubit systems which are most relevant and
sufficiently general for quantum control and computation. These invariants not
only solve the time-dependent Schr\"odinger equation of four-level systems
exactly but also enable the control, and hence quantum computation based on
which, of four-level systems fast and beyond adiabatic regimes.Comment: 11 pages, 5 table
Synthesis of perfluoroalkylene aromatic diamines
Analogues of methylene dianilines were synthesized, in which the methylene group between the two aromatic nuclei was replaced by various perfluoroalkylene linkage. The hydrolytic thermal, and thermal oxidative stabilities of PMR Polyimides derived from these diamines were determined. Three types of PMR Polyimide discs were fabricated from the dimethyl ester of 3,3', 4,4'-benzophenonetetracarboxylic acid, the methyl ester of 5-norbornene-2,3-dicarboxylic acid, and one of the following three diamines: methyl dianiline, 1,3-bis(4-aminophenyl)hexafluoropropane, and 2,2-bis(4-aminophenyl)hexafluoropropane. The polyimide based on 2,2-bis(4-aminophenyl)hexafluoropropane exhibited the best hydrolytic, thermal, and thermal oxidative stability as determined by moisture uptake and thermogravimetric analysis
Improved perfluoroalkylether fluid development
The objective of this program was to optimize and scale up the linear perfluoroalkylether stabilization process and to provide test data regarding the fluids' thermal oxidative stability in the presence of metal alloys. The stabilization of Fomblin Z-25 was scaled up to 300 g of fluid. The modified fluid was stable at 316 C in oxygen in the presence of M-50 alloy for more than 24 hrs but less than 40 hrs; the amount of volatiles produced after 24 hrs was 5.5 mg/g. In the presence of Ti(4Al,4Mn) alloy, under the above conditions, following an exposure of 24 hrs, the amount of volatiles formed was 6.2 mg/g; 56 hrs exposure yielded 13.9 mg/g. The commercial fluid at 288 C (in oxygen) in the presence of M-50 after 15 hrs of exposure decomposed extensively, 342 mg/g; in the presence of Ti(4Al,4Mn) alloy after only 8 hrs at 288 C, the amount of volatiles was 191 mg/g. Formulation of the commercial fluid with C2PN3 additive was not as effective as the stabilization processing. All the perfluoroalkylether fluids studied were stable in nitrogen at 343 C. The thermal oxidative stability in the absence of metal alloys varied, with Aflunox exhibiting the best behavior. All the fluids were degraded in oxygen at 316 C during 24 hrs exposure to Ti(4Al,4Mn) alloy with the exception of a perfluoroalkylether substituted triazine and the modified Z-25
Improved perfluoroalkylether fluid development
The feasibility of transforming a commercial linear perfluoroalkylether fluid into a material stable in the presence of metals and metal alloys in oxidizing atmospheres at 300 C without the loss of the desirable viscosity temperature characteristics was determined. The approach consisted of thermal oxidative treatment in the presence of catalyst to remove weak links, followed by transformation of the created functional groups into phospha-s-triazine linkages. It it found that the experimental material obtained in 66% yield from the commercial fluid exhibits, over an 8 hr period at 300 C in the presence of Ti(4Al, 4Mn) alloy, thermal oxidative stability better by a factor of 2.6x1000 based on volatiles evolved than the commercial product. The viscosity and molecular weight of the developed fluid are unchanged and are essentially identical with the commercial material. No metal corrosion occurs with the experimental fluid at 300 C
Bayesian approach to the first excited nucleon state in lattice QCD
We present preliminary results from the first attempt to reconstruct the
spectral function in the nucleon and channels from lattice QCD data
using the maximum entropy method (MEM). An advantage of the MEM analysis is to
enable us to access information of the excited state spectrum. Performing
simulations on two lattice volumes, we confirm the large finite size effect on
the first excited nucleon state in the lighter quark mass region.Comment: Lattice2002(spectrum), Latex with espcrc2.sty, 3 pages, 3 figure
Temporal meson correlators at finite temperature on quenched anisotropic lattice
We study charmonium correlators at finite temperature in quenched anisotropic
lattice QCD. The smearing technique is applied to enhance the low energy part
of the correlator. We use two analysis procedures: the maximum entropy method
for extraction of the spectral function without assuming specific form, as an
estimate of the shape of spectral function, and the fit assuming
typical forms as quantitative evaluation of the parameters associated to the
forms. We find that at the ground state peak has almost the
same mass as at T=0 and almost vanishing width. At , our result
suggests that the correlator still has nontrivial peak structure at almost the
same position as below with finite width.Comment: Lattice 2002 Nonzero temperature 3page
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