9,663 research outputs found
Natural Four-Generation Mass Textures in MSSM Brane Worlds
A fourth generation of Standard Model (SM) fermions is usually considered
unlikely due to constraints from direct searches, electroweak precision
measurements, and perturbative unitarity. We show that fermion mass textures
consistent with all constraints may be obtained naturally in a model with four
generations constructed from intersecting D6 branes on a T^6/(Z_2 x Z_2)
orientifold. The Yukawa matrices of the model are rank 2, so that only the
third- and fourth-generation fermions obtain masses at the trilinear level. The
first two generations obtain masses via higher-order couplings and are
therefore naturally lighter. In addition, we find that the third and fourth
generation automatically split in mass, but do not mix at leading order.
Furthermore, the SM gauge couplings automatically unify at the string scale,
and all the hidden-sector gauge groups become confining in the range
10^{13}--10^{16} GeV, so that the model becomes effectively a four-generation
MSSM at low energies.Comment: Accepted for publication in Physical Review
Dynamics of long-range order in an exciton-polariton condensate
We report on time resolved measurements of the first order spatial coherence
in an exciton polariton Bose-Einstein condensate. Long range spatial coherence
is found to set in right at the onset of stimulated scattering, on a picosecond
time scale. The coherence reaches its maximum value after the population and
decays slower, staying up to a few hundreds of picoseconds. This behavior can
be qualitatively reproduced, using a stochastic classical field model
describing interaction between the polariton condensate and the exciton
reservoir within a disordered potential.Comment: 7 pages, 4 figure
High energy green nanosecond and picosecond pulse delivery through a negative curvature fiber for precision micro-machining
Maine Distributed Solar Valuation Study
During its 2014 session, the Maine Legislature enacted an Act to Support Solar Energy Development in Maine. P.L Chapter 562 (April 24, 2014) (codified at 35âA M.R.S. §§ 3471â3473) (âActâ). Section 1 of the Act contains the Legislative finding that it is in the public interest is to develop renewable energy resources, including solar energy, in a manner that protects and improves the health and wellâbeing of the citizens and natural environment of the State while also providing economic benefits to communities, ratepayers and the overall economy of the State.
Section 2 of the Act requires the Public Utilities Commission (Commission) to determine the value of distributed solar energy generation in the State, evaluate implementation options, and to deliver a report to the Legislature. To support this work, the Commission engaged a project team comprising Clean Power Research (Napa, California), Sustainable Energy Advantage (Framingham, Massachusetts), Pace Energy and Climate Center at the Pace Law School (White Plains, New York), and Dr. Richard Perez (Albany, New York).
Under the project, the team developed the methodology under a Commissionârun stakeholder review process, conducted a valuation on distributed solar for three utility territories, and developed a summary of implementation options for increasing deployment of distributed solar generation in the State.
The report includes three volumes which accompany this Executive Summary: Volume I Methodology; Volume II Valuation Results; Volume III Implementation Options
Formation of new stellar populations from gas accreted by massive young star clusters
Stars in star clusters are thought to form in a single burst from a common
progenitor cloud of molecular gas. However, massive, old globular clusters --
with ages greater than 10 billion years and masses of several hundred thousand
solar masses -- often harbour multiple stellar populations, indicating that
more than one star-forming event occurred during their lifetimes. Colliding
stellar winds from late-stage, asymptotic-giant-branch stars are often invoked
as second-generation star-formation trigger. The initial cluster masses should
be at least 10 times more massive than they are today for this to work.
However, large populations of clusters with masses greater than a few million
solar masses are not found in the local Universe. Here we report on three 1-2
billion-year-old, massive star clusters in the Magellanic Clouds, which show
clear evidence of burst-like star formation that occurred a few hundred million
years after their initial formation era. We show that such clusters could
accrete sufficient gas reservoirs to form new stars if the clusters orbited in
their host galaxies' gaseous discs throughout the period between their initial
formation and the more recent bursts of star formation. This may eventually
give rise to the ubiquitous multiple stellar populations in globular clusters.Comment: 10 pages, 11 figures, Authors' version of a letter published in
Nature (27 January 2016), including Methods and Extended Dat
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