877 research outputs found
Cosmological constant in SUGRA models with Planck scale SUSY breaking and degenerate vacua
The empirical mass of the Higgs boson suggests small to vanishing values of the quartic Higgs self-coupling and the corresponding beta function at the Planck scale, leading to degenerate vacua. This leads us to suggest that the measured value of the cosmological constant can originate from supergravity (SUGRA) models with degenerate vacua. This scenario is realised if there are at least three exactly degenerate vacua. In the first vacuum, associated with the physical one, local supersymmetry (SUSY) is broken near the Planck scale while the breakdown of the SU(2)W×U(1)Y symmetry takes place at the electroweak (EW) scale. In the second vacuum local SUSY breaking is induced by gaugino condensation at a scale which is just slightly lower than ΛQCD in the physical vacuum. Finally, in the third vacuum local SUSY and EW symmetry are broken near the Planck scale
Mutually Unbiased Bases and Trinary Operator Sets for N Qutrits
A complete orthonormal basis of N-qutrit unitary operators drawn from the
Pauli Group consists of the identity and 9^N-1 traceless operators. The
traceless ones partition into 3^N+1 maximally commuting subsets (MCS's) of
3^N-1 operators each, whose joint eigenbases are mutually unbiased. We prove
that Pauli factor groups of order 3^N are isomorphic to all MCS's, and show how
this result applies in specific cases. For two qutrits, the 80 traceless
operators partition into 10 MCS's. We prove that 4 of the corresponding basis
sets must be separable, while 6 must be totally entangled (and Bell-like). For
three qutrits, 728 operators partition into 28 MCS's with less rigid structure
allowing for the coexistence of separable, partially-entangled, and totally
entangled (GHZ-like) bases. However, a minimum of 16 GHZ-like bases must occur.
Every basis state is described by an N-digit trinary number consisting of the
eigenvalues of N observables constructed from the corresponding MCS.Comment: LaTeX, 10 pages, 2 references adde
Partitioned trace distances
New quantum distance is introduced as a half-sum of several singular values
of difference between two density operators. This is, up to factor, the metric
induced by so-called Ky Fan norm. The partitioned trace distances enjoy similar
properties to the standard trace distance, including the unitary invariance,
the strong convexity and the close relations to the classical distances. The
partitioned distances cannot increase under quantum operations of certain kind
including bistochastic maps. All the basic properties are re-formulated as
majorization relations. Possible applications to quantum information processing
are briefly discussed.Comment: 8 pages, no figures. Significant changes are made. New section on
majorization is added. Theorem 4.1 is extended. The bibliography is enlarged
Testing the Meson Cloud Model in Inclusive Meson Production
We have applied the Meson Cloud Model to calculate inclusive momentum spectra
of pions and kaons produced in high energy proton-proton and proton-nucleus
collisions. For the first time these data are used to constrain the cloud
cut-off parameters. We show that it is possible to obtain a reasonable
description of data, especially the large () part of the
spectrum and at the same time describe (partially) the E866 data on and . We also discuss the relative strength of the
and vertices. We find out that the corresponding cut-off
parameters should be both soft and should not differ by more than 200 MeV from
each other. An additional source (other than the meson cloud) of sea antiquark
asymmetry, seems to be necessary to completely explain the data. A first
extension of the MCM to proton nucleus collisions is discussed.Comment: 14 pages, Latex, 6 ps figures. Submitted to Phys. Rev.
Encoding Synchronous Interactions Using Labelled Petri Nets
International audienceWe present an encoding of (bound) CSP processes with replication into Petri nets with labelled transitions. Through the encoding, the firing semantics of Petri nets models the standard operational semantics of CSP processes, which is both preserved and reflected. This correspondence allows for describing by net semantics the standard CSP observational equivalences. Since the encoding is modular with respect to process syntax, the paper puts on a firm ground the technology transfer between the two formalisms, e.g. recasting into the CSP framework well-established results like decidability of coverability for nets. This work complements previous results concerning the encoding of asynchronous interactions, thus witnessing the expressiveness of (open) labelled nets in modelling process calculi with alternative communication patterns
Abnormal number of Nambu-Goldstone bosons in the color-asymmetric 2SC phase of an NJL-type model
We consider an extended Nambu--Jona-Lasinio model including both (q \bar q)-
and (qq)-interactions with two light-quark flavors in the presence of a single
(quark density) chemical potential. In the color superconducting phase of the
quark matter the color SU(3) symmetry is spontaneously broken down to SU(2). If
the usual counting of Goldstone bosons would apply, five Nambu-Goldstone (NG)
bosons corresponding to the five broken color generators should appear in the
mass spectrum. Unlike that expectation, we find only three gapless diquark
excitations of quark matter. One of them is an SU(2)-singlet, the remaining two
form an SU(2)-(anti)doublet and have a quadratic dispersion law in the small
momentum limit. These results are in agreement with the Nielsen-Chadha theorem,
according to which NG-bosons in Lorentz-noninvariant systems, having a
quadratic dispersion law, must be counted differently. The origin of the
abnormal number of NG-bosons is shown to be related to a nonvanishing
expectation value of the color charge operator Q_8 reflecting the lack of color
neutrality of the ground state. Finally, by requiring color neutrality, two
massive diquarks are argued to become massless, resulting in a normal number of
five NG-bosons with usual linear dispersion laws.Comment: 13 pages, 4 figures, revtex
High-contrast imaging constraints on gas giant planet formation - The Herbig Ae/Be star opportunity
Planet formation studies are often focused on solar-type stars, implicitly
considering our Sun as reference point. This approach overlooks, however, that
Herbig Ae/Be stars are in some sense much better targets to study planet
formation processes empirically, with their disks generally being larger,
brighter and simply easier to observe across a large wavelength range. In
addition, massive gas giant planets have been found on wide orbits around early
type stars, triggering the question if these objects did indeed form there and,
if so, by what process. In the following I briefly review what we currently
know about the occurrence rate of planets around intermediate mass stars,
before discussing recent results from Herbig Ae/Be stars in the context of
planet formation. The main emphasis is put on spatially resolved polarized
light images of potentially planet forming disks and how these images - in
combination with other data - can be used to empirically constrain (parts of)
the planet formation process. Of particular interest are two objects, HD100546
and HD169142, where, in addition to intriguing morphological structures in the
disks, direct observational evidence for (very) young planets has been
reported. I conclude with an outlook, what further progress we can expect in
the very near future with the next generation of high-contrast imagers at 8-m
class telescopes and their synergies with ALMA.Comment: Accepted by Astrophysics and Space Science as invited short review in
special issue about Herbig Ae/Be stars; 12 pages incl. 5 figures, 2 tables
and reference
Sequential, successive, and simultaneous decoders for entanglement-assisted classical communication
Bennett et al. showed that allowing shared entanglement between a sender and
receiver before communication begins dramatically simplifies the theory of
quantum channels, and these results suggest that it would be worthwhile to
study other scenarios for entanglement-assisted classical communication. In
this vein, the present paper makes several contributions to the theory of
entanglement-assisted classical communication. First, we rephrase the
Giovannetti-Lloyd-Maccone sequential decoding argument as a more general
"packing lemma" and show that it gives an alternate way of achieving the
entanglement-assisted classical capacity. Next, we show that a similar
sequential decoder can achieve the Hsieh-Devetak-Winter region for
entanglement-assisted classical communication over a multiple access channel.
Third, we prove the existence of a quantum simultaneous decoder for
entanglement-assisted classical communication over a multiple access channel
with two senders. This result implies a solution of the quantum simultaneous
decoding conjecture for unassisted classical communication over quantum
multiple access channels with two senders, but the three-sender case still
remains open (Sen recently and independently solved this unassisted two-sender
case with a different technique). We then leverage this result to recover the
known regions for unassisted and assisted quantum communication over a quantum
multiple access channel, though our proof exploits a coherent quantum
simultaneous decoder. Finally, we determine an achievable rate region for
communication over an entanglement-assisted bosonic multiple access channel and
compare it with the Yen-Shapiro outer bound for unassisted communication over
the same channel.Comment: 33 pages, 2 figures; v2 contains a proof of the quantum simultaneous
decoding conjecture for two-sender quantum multiple access channels; v3 shows
how to recover the known unassisted and assisted quantum communication
regions with a coherent quantum simultaneous decode
Longitudinal study on transmission of MRSA CC398 within pig herds
Background Since the detection of MRSA CC398 in pigs in 2004, it has emerged in livestock worldwide. MRSA CC398 has been found in people in contact with livestock and thus has become a public health issue. Data from a large-scale longitudinal study in two Danish and four Dutch pig herds were used to quantify MRSA CC398 transmission rates within pig herds and to identify factors affecting transmission between pigs. Results Sows and their offspring were sampled at varying intervals during a production cycle. Overall MRSA prevalence of sows increased from 33% before farrowing to 77% before weaning. Overall MRSA prevalence of piglets was > 60% during the entire study period. The recurrent finding of MRSA in the majority of individuals indicates true colonization or might be the result of contamination. Transmission rates were estimated using a Susceptible-Infectious-Susceptible (SIS-)model, which resulted in values of the reproduction ratio (R0) varying from 0.24 to 8.08. Transmission rates were higher in pigs treated with tetracyclins and ß-lactams compared to untreated pigs implying a selective advantage of MRSA CC398 when these antimicrobials are used. Furthermore, transmission rates were higher in pre-weaning pigs compared to post-weaning pigs which might be explained by an age-related susceptibility or the presence of the sow as a primary source of MRSA CC398. Finally, transmission rates increased with the relative increase of the infection pressure within the pen compared to the total infection pressure, implying that within-pen transmission is a more important route compared to between-pen transmission and transmission through environmental exposure. Conclusion Our results indicate that MRSA CC398 is able to spread and persist in pig herds, resulting in an endemic situation. Transmission rates are affected by the use of selective antimicrobials and by the age of pigs
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