84,822 research outputs found
The Cosmological Constant Problem and Re-interpretation of Time
We abandon the interpretation that time is a global parameter in quantum
mechanics, replace it by a quantum dynamical variable playing the role of time.
This operational re-interpretation of time provides a solution to the
cosmological constant problem. The expectation value of the zero-point energy
under the new time variable vanishes. The fluctuation of the vacuum energy as
the leading contribution to the gravitational effect gives a correct order to
the observed "dark energy". The "dark energy" as a mirage is always seen
comparable with the matter energy density by an observer using the internal
clock time. Conceptual consequences of the re-interpretation of time are also
discussed.Comment: 9 pages, no figure; v3: improved discussion on remote simultaneity;
v4: improved discussion on coincidence problem, reproduced Einstein theory of
gravity from quantum reference frame, typos corrected, updated to the final
version published in Nuclear Physics
Dark Energy from Quantum Uncertainty of Distant Clock
The observed cosmic acceleration was attributed to an exotic dark energy in
the framework of classical general relativity. The dark energy behaves very
similar with vacuum energy in quantum mechanics. However, once the quantum
effects are seriously taken into account, it predicts a completely wrong result
and leads to a severe fine-tuning. To solve the problem, the exact meaning of
time in quantum mechanics is reexamined. We abandon the standard interpretation
of time in quantum mechanics that time is just a global parameter, replace it
by a quantum dynamical variable playing the role of physical clock. We find
that synchronization of two spatially separated clocks can not be precisely
realized at quantum level. There is an intrinsic quantum uncertainty of distant
clock time, which implies an apparent vacuum energy fluctuation and gives an
observed dark energy density at
tree level approximation, where and are the Planck and Hubble
scale cutoffs. The fraction of the dark energy is given by
, which does not evolve with the internal clock
time. The "dark energy" as a quantum cosmic variance is always seen comparable
with the matter energy density by an observer using the internal clock time.
The corrected distance-redshift relation of cosmic observations due to the
distant clock effect are also discussed, which again gives a redshift
independent fraction . The theory is consistent with
current cosmic observations.Comment: 7 pages, no figure; v2:added discussion on distance-redshift
relation; v3:improved discussion on distance-redshift relation, an
independent calculation to the redshift variance over redshift squared is
given, dark energy fraction agrees with 2/pi; v4:typos corrected, updated to
the final version published in Journal of High Energy Physics, Volume 2015,
Issue
Probing the QCD Critical Point with Higher Moments of Net-proton Multiplicity Distributions
Higher moments of event-by-event net-proton multiplicity distributions are
applied to search for the QCD critical point in the heavy ion collisions. It
has been demonstrated that higher moments as well as moment products are
sensitive to the correlation length and directly connected to the thermodynamic
susceptibilities computed in the Lattice QCD and Hadron Resonance Gas (HRG)
model. In this paper, we will present measurements for kurtosis (),
skewness () and variance () of net-proton multiplicity
distributions at the mid-rapidity () and GeV/ for
Au+Au collisions at =19.6, 39, 62.4, 130 and 200 GeV, Cu+Cu
collisions at =22.4, 62.4 and 200 GeV, d+Au collisions at
=200 GeV and p+p collisions at =62.4 and 200 GeV.
The moment products and of net-proton
distributions, which are related to volume independent baryon number
susceptibility ratio, are compared to the Lattice QCD and HRG model
calculations. The and of net-proton
distributions are consistent with Lattice QCD and HRG model calculations at
high energy, which support the thermalization of the colliding system.
Deviations of and for the Au+Au collisions at
low energies from HRG model calculations are also observed.Comment: 10 pages, 8 figures, Proceedings of 27th Winter Workshon on Nuclear
Dynamics. Feb. 6-13 (2011
Two-loop Renormalization Group Equations in General Gauge Field Theories
The complete set of two-loop renormalization group equations in general gauge
field theories is presented. This includes the \beta functions of parameters
with and without a mass dimension
Performance of nano-structured multilayer PVD coating TiAlN/VN in dry high speed milling of aerospace aluminium 7010-T7651
A low-friction and wear resistant TiAlN/VN multilayer coating with TiAlN/VN bilayer thickness 3 nm has been grown by using the combined cathodic arc etching and unbalanced magnetron sputtering deposition on high speed steel tools for dry cutting of aluminium alloys. In this paper, in-lab and industrial high speed milling tests have been performed on an aerospace aluminium alloy 7010-T7651. The results show that the TiAlN/VN coated tools achieved lower cutting forces, lower metal surface roughness, and significantly longer tool lifetime by three times over the uncoated tools as a result of the low friction and eliminated tool-metal adhesion. Under the same conditions, a TiAlN based multicomponent coating TiAlCrYN also increased the tool lifetime by up to 100% despite the high cutting forces measured
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