24 research outputs found
A bi-objective model for the single-machine scheduling problem with rejection cost and total tardiness minimization
We study the problem of scheduling jobs on a single machine with a rejection possibility, concurrently minimizing the total tardiness of the scheduled jobs and the total cost of the rejected ones. The model we consider is fully bi-objective, i.e. its aim is to enumerate the Pareto front. We tackle the problem both with and without the presence of hard deadlines. For the case without deadlines, we provide a pseudo-polynomial time algorithm, based on the dynamic program of Steiner and Zhang (2011), thereby proving that the problem is weakly NP-hard. For the case with deadlines, we propose a branch-and-bound algorithm and prove its efficiency by comparing it to an \u3b5-constrained approach on benchmark instances based on those proposed in the literature on similar problems
Leptogenesis in SO(10) models with a left-right symmetric seesaw mechanism
We study leptogenesis in supersymmetric SO(10) models with a left-right
symmetric seesaw mechanism, including flavour effects and the contribution of
the next-to-lightest right-handed neutrino. Assuming M_D = M_u and hierarchical
light neutrino masses, we find that successful leptogenesis is possible for 4
out of the 8 right-handed neutrino mass spectra that are compatible with the
observed neutrino data. An accurate description of charged fermion masses
appears to be an important ingredient in the analysis.Comment: Submitted for the SUSY07 proceedings, 4 pages, 9 figure
Examining leptogenesis with lepton flavor violation and the dark matter abundance
Within a supersymmetric (SUSY) type-I seesaw framework with flavor-blind
universal boundary conditions, we study the consequences of requiring that the
observed baryon asymmetry of the Universe be explained by either thermal or
non-thermal leptogenesis. In the former case, we find that the parameter space
is very constrained. In the bulk and stop-coannihilation regions of mSUGRA
parameter space (that are consistent with the measured dark matter abundance),
lepton flavor-violating (LFV) processes are accessible at MEG and future
experiments. However, the very high reheat temperature of the Universe needed
after inflation (of about 10^{12} GeV) leads to a severe gravitino problem,
which disfavors either thermal leptogenesis or neutralino dark matter.
Non-thermal leptogenesis in the preheating phase from SUSY flat directions
relaxes the gravitino problem by lowering the required reheat temperature. The
baryon asymmetry can then be explained while preserving neutralino dark matter,
and for the bulk or stop-coannihilation regions LFV processes should be
observed in current or future experiments.Comment: 20 pages, 5 figures, 1 tabl
Searching singlet extensions of the supersymmetric standard model in orbifold compactification of heterotic string
We search for supersymmetric standard model realizations with extra singlets
and extra using the heterotic string compactification on the orbifold with two Wilson lines. We analyze the vacuum restabilization
mechanism for three representative Pati-Salam string models obtained in the
literature and present detailed results for the effective superpotential
compatible with the string selection rules. An automated selection of
semi-realistic vacua along flat directions in the non-Abelian singlet modes
field space is performed by requiring the presence of massless pairs of
electroweak Higgs bosons having trilinear superpotential couplings with
massless singlet modes and the decoupling of color triplet exotic modes needed
to suppress and number violating processes.Comment: revtex4 format, 21 pages, 7 tables, shortened version added
reference
Neutrino physics overview
Seesaw-type and low-scale models of neutrino masses are reviewed, along with
the corresponding structure of the lepton mixing matrix.
The status of neutrino oscillation parameters as of June 2006 is given,
including recent fluxes, as well as latest SNO, K2K and MINOS results. Some
prospects for the next generation of experiments are given. This writeup
updates the material presented in my lectures at the Corfu Summer Institute on
Elementary Particle Physics in September 2005.Comment: Review based on lectures at the Corfu Summer Institute on Elementary
Particle Physics in September 2005. To be published in the Proceeding
The stochastic critical node problem over trees
We tackle a stochastic version of the critical node problem (CNP) where the goal is to minimize the pairwise connectivity of a graph by attacking a subset of its nodes. In the stochastic setting considered, the outcome of attacks on nodes is uncertain. In our work, we focus on trees and demonstrate that over trees the stochastic CNP actually generalizes to the stochastic critical element detection problem where the outcome of attacks on edges is also uncertain. We prove the NP-completeness of the decision version of the problem when connection costs are one, while its deterministic counterpart was proved to be polynomial. We then derive a nonlinear model for the considered CNP version over trees and provide a corresponding linearization based on the concept of probability chains. Moreover, given the features of the derived linear model, we devise an exact Benders decomposition (BD) approach where we solve the slave subproblems analytically. A strength of our approach is that it does not rely on any statistical approximation such as the sample average approximation, which is commonly employed in stochastic optimization. We also introduce an approximation algorithm for the problem variant with unit connection costs and unit attack costs, and a specific integer linear model for the case where all the survival probabilities of the nodes in case of an attack are equal. Our methods are capable of solving relevant instances of the problem with hundreds of nodes within 1 hour of computational time. With this work, we aim to foster research on stochastic versions of the CNP, a problem tackled mainly in deterministic contexts so far. Interestingly, we also show a successful application of the concept of probability chains for problem linearizations significantly improved by decomposition methods such as the BD