5,703 research outputs found
Leptonic decay-constant ratio f_{K^+}/f_{pi^+} from lattice QCD with physical light quarks
A calculation of the ratio of leptonic decay constants f_{K^+}/f_{\pi^+}
makes possible a precise determination of the ratio of CKM matrix elements
|V_{us}|/|V_{ud}| in the Standard Model, and places a stringent constraint on
the scale of new physics that would lead to deviations from unitarity in the
first row of the CKM matrix. We compute f_{K^+}/f_{\pi^+} numerically in
unquenched lattice QCD using gauge-field ensembles recently generated that
include four flavors of dynamical quarks: up, down, strange, and charm. We
analyze data at four lattice spacings a ~ 0.06, 0.09, 0.12, and 0.15 fm with
simulated pion masses down to the physical value 135 MeV. We obtain
f_{K^+}/f_{\pi^+} = 1.1947(26)(37), where the errors are statistical and total
systematic, respectively. This is our first physics result from our N_f = 2+1+1
ensembles, and the first calculation of f_{K^+}/f_{\pi^+} from lattice-QCD
simulations at the physical point. Our result is the most precise lattice-QCD
determination of f_{K^+}/f_{\pi^+}, with an error comparable to the current
world average. When combined with experimental measurements of the leptonic
branching fractions, it leads to a precise determination of |V_{us}|/|V_{ud}| =
0.2309(9)(4) where the errors are theoretical and experimental, respectively.Comment: 6 pages, 1 table, 2 figures; v3: result for f_{K^+}/f_{pi^+} updated
to include additional data; typo in some values of L in Table 1 corrected;
typo in sign of 1-|V_{ud}|^2-|V_{us}|^2-|V_{ub}|^2 corrected; version to be
published in Phys. Rev. Let
Field-induced water electrolysis switches an oxide semiconductor from an insulator to a metal
Here we demonstrate that water-infiltrated nanoporous glass electrically
switches an oxide semiconductor from an insulator to metal. We fabricated the
field effect transistor structure on an oxide semiconductor, SrTiO3, using
100%-water-infiltrated nanoporous glass - amorphous 12CaO*7Al2O3 - as the gate
insulator. For positive gate voltage, electron accumulation, water electrolysis
and electrochemical reduction occur successively on the SrTiO3 surface at room
temperature, leading to the formation of a thin (~3 nm) metal layer with an
extremely high electron concentration of 10^15-10^16 cm^-2, which exhibits
exotic thermoelectric behaviour.Comment: 21 pages, 12 figure
Phase Space Structure of Generalized Gaussian Cat States
We analyze generalized Gaussian cat states obtained by superposing arbitrary
Gaussian states, e.g., a coherent state and a squeezed state. The Wigner
functions of such states exhibit the typical pair of Gaussian hills plus an
interference term which presents a novel structure, as compared with the
standard superposition of coherent states (degenerate case). We prove that, in
any dimensions, the structure of the interference term is characterized by a
particular quadratic form; in one degree of freedom the phase is hyperbolic.
This phase-space structure survives the action of a thermal reservoir. We also
discuss certain superpositions of {\em mixed} Gaussian states generated by
conditional Gaussian operations or Kerr-type dynamics on thermal states.Comment: 12 pages, 6 figures, submitted to Physical Review
Charmed and light pseudoscalar meson decay constants from four-flavor lattice QCD with physical light quarks
We compute the leptonic decay constants fD+, fDs, and fK+ and the quark-mass ratios mc/ms and ms/ml in unquenched lattice QCD using the experimentally determined value of fπ+ for normalization. We use the MILC highly improved staggered quark ensembles with four dynamical quark flavors—up, down, strange, and charm—and with both physical and unphysical values of the light sea-quark masses. The use of physical pions removes the need for a chiral extrapolation, thereby eliminating a significant source of uncertainty in previous calculations. Four different lattice spacings ranging from a≈0.06 to 0.15 fm are included in the analysis to control the extrapolation to the continuum limit. Our primary results are fD+=212.6(0.4)(+1.0−1.2)  MeV, fDs=249.0(0.3)(+1.1−1.5)  MeV, and fDs/fD+=1.1712(10)(+29−32), where the errors are statistical and total systematic, respectively. The errors on our results for the charm decay constants and their ratio are approximately 2–4 times smaller than those of the most precise previous lattice calculations. We also obtain fK+/fπ+=1.1956(10)(+26−18), updating our previous result, and determine the quark-mass ratios ms/ml=27.35(5)(+10−7) and mc/ms=11.747(19)(+59−43). When combined with experimental measurements of the decay rates, our results lead to precise determinations of the Cabibbo-Kobayashi-Maskawa matrix elements |Vus|=0.22487(51)(29)(20)(5), |Vcd|=0.217(1)(5)(1) and |Vcs|=1.010(5)(18)(6), where the errors are from this calculation of the decay constants, the uncertainty in the experimental decay rates, structure-dependent electromagnetic corrections, and, in the case of |Vus|, the uncertainty in |Vud|, respectively
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