Tree-level metastability bounds for the most general two Higgs doublet model

Within two Higgs doublet models, it is possible that the current vacuum is not the global minimum, in which case it could possibly decay at a later stage. We discuss the tree-level conditions which must be obeyed by the most general scalar potential in order to preclude that possibility. We propose a new procedure which is not only more general but also easier to implement than the previously published one, including CP conserving as well as CP violating scalar sectors. We illustrate these conditions within the context of the Z2 model, softly broken by a complex, CP violating parameter.Comment: RevTex, 13 pages, 3 figure

A CP-conserving multi-Higgs model without real basis

Models beyond the Standard Model (bSM) often involve elaborate Higgs sectors, which can be a source of CP-violation. It brings up the question of recognizing in an efficient way whether a model is CP-violating. There is a diffuse belief that the issue of explicit CP invariance can be linked to the existence of a basis in which all coefficients are real; with even a theorem proposed a decade ago claiming that the scalar sector of any multi-Higgs doublet model is explicitly CP-conserving if and only if all of its coefficients can be made real by a basis change. This is compounded by the fact that in all specific multi Higgs models considered so far, the calculations complied with this claim. Here, we present the first counterexample to this statement: a CP-conserving three-Higgs-doublet model for which no real basis exists. We outline the phenomenological consequences of this model, and notice that the extra neutral Higgs bosons are neither CP-even nor CP-odd but are "half-odd" under the generalized CP-symmetry of the model.Comment: 6 pages; v2: abstract, introduction, conclusions reformulated, all the results stay unchange

The present development of time service in Brazil, with the application of the TV line-10 method for coordination and synchronization of atomic clocks

Various methods presently used for the dissemination of time at several levels of precision are described along with future projects in the field. Different aspects of time coordination are reviewed and a list of future laboratories participating in a National Time Scale will be presented. A Brazilian Atomic Time Scale will be obtained from as many of these laboratories as possible. The problem of intercomparison between the Brazilian National Time Scale and the International one will be presented and probable solutions will be discussed. Needs related to the TV Line-10 method will be explained and comments will be made on the legal aspects of time dissemination throughout the country

On Computing Minimum Unsatisfiable Cores

Certifying the correctness of a SAT solver is straightforward for satisfiable instances of SAT. Given

An Overview of Backtrack Search Satisfiability Algorithms

Propositional Satisfiability (SAT) is often used as the underlying model for a significan

Hidden Structure in Unsatisfiable Random 3-SAT: an Empirical Study

Recent advances in propositional satisfiability (SAT) include studying the hidden structure of unsatisfiable formulas, i.e. explaining why a given formula is unsatisfiable. Although theoretical work on the topic has been developed in the past, only recently two empirical successful approaches have been proposed: extracting unsatisfiable cores and identifying strong backdoors. An unsatisfiable core is a subset of clauses that defines a sub-formula that is also unsatisfiable, whereas a strong backdoor defines a subset of variables which assigned with all values allow concluding that the formula is unsatisfiable. The contribution of this paper is two-fold. First, we study the relation between the search complexity of unsatisfiable random 3-SAT formulas and the sizes of unsatisfiable cores and strong backdoors. For this purpose, we use an existing algorithm which uses an approximated approach for calculating these values. Second, we introduce a new algorithm that optimally reduces the size of unsatisfiable cores and strong backdoors, thus giving more accurate results. Experimental results indicate that the search complexity of unsatisfiable random 3-SAT formulas is related with the size of unsatisfiable cores and strong backdoors. 1

Probing-Based Preprocessing Techniques for Propositional Satisfiability

Preprocessing is an often used approach for solving hard instances of propositional satisfiability (SAT). Preprocessing can be used for reducing the number of variables and for drastically modifying the set of clauses, either by eliminating irrelevant clauses or by inferring new clauses. Over the years, a large number of formula manipulation techniques has been proposed, that in some situations have allowed solving instances not otherwise solvable with stateof -the-art SAT solvers. This paper proposes probing-based preprocessing, an integrated approach for preprocessing propositional formulas, that for the first time integrates in a single algorithm most of the existing formula manipulation techniques. Moreover, the new unified framework can be used to develop new techniques. Preliminary experimental results illustrate that probing-based preprocessing can be effectively used as a preprocessing tool in state-of-theart SAT solvers