5,189 research outputs found

### Algebras and non-geometric flux vacua

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 $hh\rightarrow b\bar{b} \; WW \rightarrow b\bar{b} \ell^+ \nu \ell^- \bar\nu$ decay channel

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 $hh \rightarrow b
\bar{b} WW \rightarrow b \bar{b} \ell^+ \nu \ell^- \bar{\nu}$ 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 4$b$ 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 $M_{\rm
T2}$ and the $M_{\rm T2}$-assisted on-shell reconstruction of invisible
momenta. Using proper cuts, a significance of $\sim$ 3$\sigma$ for 3000
fb$^{-1}$ can be achieved at the 14 TeV LHC for $m_H$ = 260 - 400 GeV if the
mixing is close to its present limit and ${\rm BR}(H \rightarrow hh) \approx
1$. Smaller mixing values would require combining various decay channels in
order to reach a similar significance. The complementarity among $H
\rightarrow hh$, $H \rightarrow ZZ$ and $H \rightarrow WW$ channels is
studied for arbitrary ${\rm BR}(H \rightarrow hh)$ values.Comment: 36 pages, 13 figure

### Reducing the fine-tuning of gauge-mediated SUSY breaking

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, $A_t=0$. 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 $A_t\neq 0$
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 $A_t$ 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 $A_t^2/m^2$
problem", i.e. the fact that a large $A_t$-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

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?

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
${\cal O}(1\%)$. However, this result presents a strong dependence on the HE
scale. E.g. if the latter is $10^7$ 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 ${\cal O}(1\%)$ or milder. Incidentally, this upper bound is not
far from $\simeq1$ 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

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 (2Ã—2, 4Ã—4, 10Ã—10 and 3Ã—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 2Ã—2 and 10Ã—10 cm2 fields. We found that the MLC contribution to the total build-up dose is about 2% for the 2Ã—2 cm2 field and less than 1% for the largest fields

### Analyzing Fuzzy Logic Computations with Fuzzy XPath

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

- â€¦