5,189 research outputs found

    Algebras and non-geometric flux vacua

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    In this work we classify the subalgebras satisfied by non-geometric Q-fluxes in type IIB orientifolds on T^6/(Z_2 x Z_2) with three moduli (S,T,U). We find that there are five subalgebras compatible with the symmetries, each one leading to a characteristic flux-induced superpotential. Working in the 4-dimensional effective supergravity we obtain families of supersymmetric AdS_4 vacua with all moduli stabilized at small string coupling g_s. Our results are mostly analytic thanks to a judicious parametrization of the non-geometric, RR and NSNS fluxes. We are also able to leave the flux-induced C_4 and C_8 RR tadpoles as free variables, thereby enabling us to study which values are allowed for each Q-subalgebra. Another novel outcome is the appearance of multiple vacua for special sets of fluxes. However, they generically have g_s > 1 unless the net number of O3/D3 or O7/D7 sources needed to cancel the tadpoles is large. We also discuss briefly the issues of axionic shift symmetries and cancellation of Freed-Witten anomalies.Comment: 61 pages, LaTex, v2: added reference

    Resonant Higgs boson pair production in the hh→bbˉ  WW→bbˉℓ+νℓ−νˉhh\rightarrow b\bar{b} \; WW \rightarrow b\bar{b} \ell^+ \nu \ell^- \bar\nu decay channel

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    Adding a scalar singlet provides one of the simplest extensions of the Standard Model. In this work we briefly review the latest constraints on the mass and mixing of the new Higgs boson and study its production and decay at the LHC. We mainly focus on double Higgs production in the hh→bbˉWW→bbˉℓ+νℓ−νˉhh \rightarrow b \bar{b} WW \rightarrow b \bar{b} \ell^+ \nu \ell^- \bar{\nu} decay channel. This decay is found to be efficient in a region of masses of the heavy Higgs boson of 260 - 500 GeV, so it is complementary to the 4bb channel, more efficient for Higgs bosons having masses greater than 500 GeV. We analyse this di-leptonic decay channel in detail using kinematic variables such as MT2M_{\rm T2} and the MT2M_{\rm T2}-assisted on-shell reconstruction of invisible momenta. Using proper cuts, a significance of ∼\sim 3σ\sigma for 3000 fb−1^{-1} can be achieved at the 14 TeV LHC for mHm_H = 260 - 400 GeV if the mixing is close to its present limit and BR(H→hh)≈1{\rm BR}(H \rightarrow hh) \approx 1. Smaller mixing values would require combining various decay channels in order to reach a similar significance. The complementarity among H→hh H \rightarrow hh, H→ZZ H \rightarrow ZZ and H→WW H \rightarrow WW channels is studied for arbitrary BR(H→hh){\rm BR}(H \rightarrow hh) values.Comment: 36 pages, 13 figure

    Reducing the fine-tuning of gauge-mediated SUSY breaking

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    Despite their appealing features, models with gauge-mediated supersymmetry breaking (GMSB) typically present a high degree of fine-tuning, due to the initial absence of the top trilinear scalar couplings, At=0A_t=0. In this paper, we carefully evaluate such a tuning, showing that is worse than per mil in the minimal model. Then, we examine some existing proposals to generate At≠0A_t\neq 0 term in this context. We find that, although the stops can be made lighter, usually the tuning does not improve (it may be even worse), with some exceptions, which involve the generation of AtA_t at one loop or tree level. We examine both possibilities and propose a conceptually simplified version of the latter; which is arguably the optimum GMSB setup (with minimal matter content), concerning the fine-tuning issue. The resulting fine-tuning is better than one per mil, still severe but similar to other minimal supersymmetric standard model constructions. We also explore the so-called "little At2/m2A_t^2/m^2 problem", i.e. the fact that a large AtA_t-term is normally accompanied by a similar or larger sfermion mass, which typically implies an increase in the fine-tuning. Finally, we find the version of GMSB for which this ratio is optimized, which, nevertheless, does not minimize the fine-tuning.Comment: 16 pages, 11 figures, 1 appendix. Discussion extended, matches EPJC published versio

    Economic Fluctuations, Child Mortality and Policy Considerations in the Least Developed Countries

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    Between 1990 and 2010 child mortality decreased in general terms in the Least Developed Countries (LDCs), although the differences between countries over time are significant. This paper examines the relationship between short-term economic fluctuations and changes in child mortality in the LDCs during the period 1990-2010. Unlike other studies, we consider a large group of LDCs and provide empirical evidence of the asymmetrical effects of variations in Gross Domestic Product per capita on the evolution of child mortality rate in periods of economic recession and expansion. The significance of said effects diminishes when other relevant socio-economic control variables are considered, and some development policy considerations are addressed in order to achieve the Millennium Development Goal 4 target

    What is a Natural SUSY scenario?

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    The idea of "Natural SUSY", understood as a supersymmetric scenario where the fine-tuning is as mild as possible, is a reasonable guide to explore supersymmetric phenomenology. In this paper, we re-examine this issue in the context of the MSSM including several improvements, such as the mixing of the fine-tuning conditions for different soft terms and the presence of potential extra fine-tunings that must be combined with the electroweak one. We give tables and plots that allow to easily evaluate the fine-tuning and the corresponding naturalness bounds for any theoretical model defined at any high-energy (HE) scale. Then, we analyze in detail the complete fine-tuning bounds for the unconstrained MSSM, defined at any HE scale. We show that Natural SUSY does not demand light stops. Actually, an average stop mass below 800 GeV is disfavored, though one of the stops might be very light. Regarding phenomenology, the most stringent upper bound from naturalness is the one on the gluino mass, which typically sets the present level of fine-tuning at O(1%){\cal O}(1\%). However, this result presents a strong dependence on the HE scale. E.g. if the latter is 10710^7 GeV the level of fine-tuning is ∼\sim four times less severe. Finally, the most robust result of Natural SUSY is by far that Higgsinos should be rather light, certainly below 700 GeV for a fine-tuning of O(1%){\cal O}(1\%) or milder. Incidentally, this upper bound is not far from ≃1\simeq1 TeV, which is the value required if dark matter is made of Higgsinos.Comment: 41 pages, 8 figures, 9 tables. References added, matches JHEP published versio

    Assesing multileaf collimator effect on the build-up region using Monte Carlo method

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    Previous Monte Carlo studies have investigated the multileaf collimator (MLC) contribution to the build-up region for fields in which the MLC leaves were fully blocking the openings defined by the collimation jaws. In the present work, we investigate the same effect but for symmetric and asymmetric MLC defined field sizes (2×2, 4×4, 10×10 and 3×7 cm2). A Varian 2100C/D accelerator with 120-leaf MLC is accurately modeled fora6MVphoton beam using the BEAMnrc/EGSnrc code. Our results indicate that particles scattered from accelerator head and MLC are responsible for the increase of about 7% on the surface dose when comparing 2×2 and 10×10 cm2 fields. We found that the MLC contribution to the total build-up dose is about 2% for the 2×2 cm2 field and less than 1% for the largest fields

    Analyzing Fuzzy Logic Computations with Fuzzy XPath

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    Implemented with a fuzzy logic language by using the FLOPER tool developed in our research group, we have recently designed a fuzzy dialect of the popular XPath language for the flexible manipulation of XML documents. In this paper we focus on the ability of Fuzzy XPath for exploring derivation trees generated by FLOPER once they are exported in XML format, which somehow serves as a debugging/analizing tool for discovering the set of fuzzy computed answers for a given goal, performing depth/breadth-first traversals of its associated derivation tree, finding non fully evaluated branches, etc., thus reinforcing the bi-lateral synergies between Fuzzy XPath and FLOPER
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