170 research outputs found
Dynamically Warped Theory Space and Collective Supersymmetry Breaking
We study deconstructed gauge theories in which a warp factor emerges
dynamically and naturally. We present nonsupersymmetric models in which the
potential for the link fields has translational invariance, broken only by
boundary effects that trigger an exponential profile of vacuum expectation
values. The spectrum of physical states deviates exponentially from that of the
continuum for large masses; we discuss the effects of such exponential towers
on gauge coupling unification. We also present a supersymmetric example in
which a warp factor is driven by Fayet-Iliopoulos terms. The model is peculiar
in that it possesses a global supersymmetry that remains unbroken despite
nonvanishing D-terms. Inclusion of gravity and/or additional messenger fields
leads to the collective breaking of supersymmetry and to unusual phenomenology.Comment: 28 pages LaTeX, JHEP format, 7 eps figures (v2: reference added
Z boson pair production at LHC in a stabilized Randall-Sundrum scenario
We study the Z boson pair production at LHC in the Randall-Sundrum scenario
with the Goldberger-Wise stabilization mechanism. It is shown that
comprehensive account of the Kaluza-Klein graviton and radion effects is
crucial to probe the model: The KK graviton effects enhance the cross section
of on the whole so that the resonance peak of the radion becomes
easy to detect, whereas the RS effects on the process are
rather insignificant. The and invariant-mass distributions are presented
to study the dependence of the RS model parameters. The production of
longitudinally polarized Z bosons, to which the SM contributions are
suppressed, is mainly due to KK gravitons and the radion, providing one of the
most robust methods to signal the RS effects. The sensitivity bounds
on with are also obtained such that
the effective weak scale of order 5 TeV can be experimentally
probed.Comment: 28 pages, LaTex file, 18 eps figure
How Fitch-Margoliash Algorithm can Benefit from Multi Dimensional Scaling
Whatever the phylogenetic method, genetic sequences are often described as strings of characters, thus molecular sequences can be viewed as elements of a multi-dimensional space. As a consequence, studying motion in this space (ie, the evolutionary process) must deal with the amazing features of high-dimensional spaces like concentration of measured phenomenon
Silicon and Germanium Nanostructures for Photovoltaic Applications: Ab-Initio Results
Actually, most of the electric energy is being produced by fossil fuels and great is the search for viable alternatives. The most appealing and promising technology is photovoltaics. It will become truly mainstream when its cost will be comparable to other energy sources. One way is to significantly enhance device efficiencies, for example by increasing the number of band gaps in multijunction solar cells or by favoring charge separation in the devices. This can be done by using cells based on nanostructured semiconductors. In this paper, we will present ab-initio results of the structural, electronic and optical properties of (1) silicon and germanium nanoparticles embedded in wide band gap materials and (2) mixed silicon-germanium nanowires. We show that theory can help in understanding the microscopic processes important for devices performances. In particular, we calculated for embedded Si and Ge nanoparticles the dependence of the absorption threshold on size and oxidation, the role of crystallinity and, in some cases, the recombination rates, and we demonstrated that in the case of mixed nanowires, those with a clear interface between Si and Ge show not only a reduced quantum confinement effect but display also a natural geometrical separation between electron and hole
Quarkonium Physics at a Fixed-Target Experiment using the LHC Beams
We outline the many quarkonium-physics opportunities offered by a
multi-purpose fixed-target experiment using the p and Pb LHC beams extracted by
a bent crystal. This provides an integrated luminosity of 0.5 fb-1 per year on
a typical 1cm-long target. Such an extraction mode does not alter the
performance of the collider experiments at the LHC. With such a high
luminosity, one can analyse quarkonium production in great details in pp, pd
and pA collisions at sqrt(sNN)~115 GeV and at sqrt(sNN)~72 GeV in PbA
collisions. In a typical pp (pA) run, the obtained quarkonium yields per unit
of rapidity are 2-3 orders of magnitude larger than those expected at RHIC and
about respectively 10 (70) times larger than for ALICE. In PbA, they are
comparable. By instrumenting the target-rapidity region, the large negative-xF
domain can be accessed for the first time, greatly extending previous
measurements by Hera-B and E866. Such analyses should help resolving the
quarkonium-production controversies and clear the way for gluon PDF extraction
via quarkonium studies. The nuclear target-species versatility provides a
unique opportunity to study nuclear matter and the features of the hot and
dense matter formed in PbA collisions. A polarised proton target allows the
study of transverse-spin asymmetries in J/psi and Upsilon production, providing
access to the gluon and charm Sivers functions.Comment: Proceedings of the workshop "30 years of strong interactions", Spa,
Belgium, 6-8 April 2011. Version to appear in Few-Body Systems. 14 pages, 2
tables, LaTe
Research trends in combinatorial optimization
Acknowledgments This work has been partially funded by the Spanish Ministry of Science, Innovation, and Universities through the project COGDRIVE (DPI2017-86915-C3-3-R). In this context, we would also like to thank the Karlsruhe Institute of Technology. Open access funding enabled and organized by Projekt DEAL.Peer reviewedPublisher PD
Physical Processes in Star Formation
© 2020 Springer-Verlag. The final publication is available at Springer via https://doi.org/10.1007/s11214-020-00693-8.Star formation is a complex multi-scale phenomenon that is of significant importance for astrophysics in general. Stars and star formation are key pillars in observational astronomy from local star forming regions in the Milky Way up to high-redshift galaxies. From a theoretical perspective, star formation and feedback processes (radiation, winds, and supernovae) play a pivotal role in advancing our understanding of the physical processes at work, both individually and of their interactions. In this review we will give an overview of the main processes that are important for the understanding of star formation. We start with an observationally motivated view on star formation from a global perspective and outline the general paradigm of the life-cycle of molecular clouds, in which star formation is the key process to close the cycle. After that we focus on the thermal and chemical aspects in star forming regions, discuss turbulence and magnetic fields as well as gravitational forces. Finally, we review the most important stellar feedback mechanisms.Peer reviewedFinal Accepted Versio
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