Non-SUSY WIMPS: simplified models and Dark Matter at the LHC

I discuss the construction of Simplified Models for Dark Matter searches at the LHC. After reviewing the phylosophy and some simple example, I turn the attention to the aspect of the theoretical consistency of these models.Comment: Proceedings of 13th Rencontres du Vietnam on Exploring the Dark Univers

On the Validity of the EFT for Dark Matter Searches at the LHC

We review the limitations to the use of the effective field theory approach to study dark matter at the LHC. Due to the high energy reach, the low energy description breaks down, and may lead to incorrect results. The use of simplified models is suggested.Comment: Prepared for the Proceedings of IFAE 2014, L'Aquila, April 201

Relaxion Dark Matter

We highlight a new connection between the Standard Model hierarchy problem and the dark matter sector. The key piece is the relaxion field, which besides scanning the Higgs mass and setting the electroweak scale, also constitutes the observed dark matter abundance of the universe. The relaxation mechanism is realized during inflation, and the necessary friction is provided by particle production. Using this framework we show that the relaxion is a phenomenologically viable dark matter candidate in the keV mass range.Comment: 11 pages, 2 figures, 1 table; v2: extended discussion, parameter space includes larger masses and higher reheating temperatures than in v1, matches version accepted by PRD; v3: numerical error corrected, table and figures updated, conclusions unchange

The 750 GeV Diphoton excess, Dark Matter and Constraints from the IceCube experiment

Recent LHC data show hints of a new resonance in the diphoton distribution at an invariant mass of 750 GeV. Interestingly, this new particle might be both CP odd and play the role of a portal into the dark matter sector. Under these assumptions and motivated by the fact that the requirement of $SU(2)_L$ invariance automatically implies the coupling of this alleged new resonance to $ZZ$ and $Z\gamma$, we investigate the current and future constraints coming from the indirect searches performed through the neutrino telescope IceCube. We show that these constraints can be stronger than the ones from direct detection experiments if the dark matter mass is larger than a few hundred GeV. Furthermore, in the scenario in which the dark matter is a scalar particle, the IceCube data limit the cross section between the DM and the proton to values close to the predicted ones for natural values of the parameters.Comment: 20 pages, 6 figures; v2: added references; v3: published version, with some minor edits and including the exclusion bounds from searches of gamma ray

Standing Waves in a Non-linear 1D Lattice : Floquet Multipliers, Krein Signatures, and Stability

We construct a class of exact commensurate and incommensurate standing wave (SW) solutions in a piecewise smooth analogue of the discrete non-linear Schr\"{o}dinger (DNLS) model and present their linear stability analysis. In the case of the commensurate SW solutions the analysis reduces to the eigenvalue problem of a transfer matrix depending parametrically on the eigenfrequency. The spectrum of eigenfrequencies and the corresponding eigenmodes can thereby be determined exactly. The spatial periodicity of a commensurate SW implies that the eigenmodes are of the Bloch form, characterised by an even number of Floquet multipliers. The spectrum is made up of bands that, in general, include a number of transition points corresponding to changes in the disposition of the Floquet multipliers. The latter characterise the different band segments. An alternative characterisation of the segments is in terms of the Krein signatures associated with the eigenfrequencies. When one or more parameters characterising the SW solution is made to vary, one occasionally encounters collisions between the band-edges or the intra-band transition points and, depending on the the Krein signatures of the colliding bands or segments, the spectrum may stretch out in the complex plane, leading to the onset of instability. We elucidate the correlation between the disposition of Floquet multipliers and the Krein signatures, presenting two specific examples where the SW possesses a definite window of stability, as distinct from the SW's obtained close to the anticontinuous and linear limits of the DNLS model.Comment: 31 pages, 11 figure

50 años de Antropología en el Museo de Ciencias Naturales de La Plata: historia, desafíos y perspectivas. En: Avá, n° 14

Recientemente y en diferentes contextos, los antropólogos argentinos comenzaron a discutir acerca del perfil profesional. La formación universitaria, las demandas e inserción en diversos sectores sociales fueron conciliados para definir nuevas perspectivas en el desarrollo disciplinar. La Carrera de Antropología se inicia en el Museo de Ciencias Naturales de La Plata en 1958, con una orientación teórica definida en el marco de las Ciencias Naturales. Ello ha aportado interesantes enfoques que posibilitan la intervención del antropólogo en proyectos y programas interdisciplinarios. El presente trabajo intenta dar cuenta del proceso de revisión de nuestra historia institucional. Esperamos contribuir a la consolidación de espacios formales de discusión y organización para superar la fragmentación que aún se advierte pese a los cincuenta años transcurridos de la creación de las carreras de Antropología en nuestro país

Serratia marcescens, the “Flame” Strain: The Genesis of a New Variant A Newly Described Strain with Prolific Pigment Produced at High Temperature

Serratia marcescens, a Gram-negative, rod-shaped, facultative anaerobe (Fig. 1), is ubiquitous in water, soil, and natural settings. It is easily grown in the lab and may serve as an ideal model for adaptation studies because of the natural color variation of S. marcescens (Gillen 2008). In this paper, we describe a new variant with prolific pigment (prodigiosin) production at high temperatures. In the wild and in buildings, S. marcescens is noted for the production of a bright red pigment called prodigiosin (Williams 1973). We have found a new strain that appears to have adapted to a relatively new pond system called Liberty Library Lake. It produces pigment up to 40°C without any enrichment to media. Most wild-type strains, like NIMA, produce pigment normally up to 30°C, but with extensive enrichment, wild-type strains can produce pigment up to 40°C. This new strain, called the “Flame” strain, not only produces prodigiosin to 39–40°C but also in higher abundance at 35°C and at a brighter hue. NIMA strains can produce pigment at 39–40°C with Serratia Synergy Agar (glycerol, peptone, agar) but not on TSA nor any common agar. It takes significant enhancement for any other Serratia marcescens strains to produce pigment even at 35°C. The Flame strain’s brief appearance in a local, small lake appears to be a phenotypic diversification and adaptation to an environmental perturbation this past school year. The environmental stress prior to its appearance was an autumn drought. Eventually, heavy rainfall occurred and the new strain was discovered. Its appearance coincided with an unusually high abundance of coliforms, avian Giardia, and Cryptosporidium, along with chemical treatment of the lake. The unusual conditions seem to favor a rapid phenotypic diversification and adaptation. The new strain still retains the pigment production at nearly 10°C higher for “normal” prodigiosin production by wild-type Serratia marcescens. This genesis of this new strain seems to have occurred as special conditions favored this new variant. It may be closer to a “proto-type” (ancestral) strain than to more common wild-type strains, like NIMA and BS303. It appears that most wild-type strains, like NIMA and BS303, may have lost this information over time since added enrichment is necessary to produce pigment at 39–40°C. The unusual conditions may have selected for this newly adapted strain to be common for a short time. Also as conditions returned to “normal,” a common wild-type strain reappeared at the local lake, and the Flame strain was no longer found. The objective of this article is to explain the mysterious origin of a new strain of Serratia marcescens that produces prodigiosin up to 40°C without any enrichment to media. This strain can naturally produce prolific pigment that is a bright, flame-red. Since Serratia marcescens offers protection from other microbes, UV light, and drought, it is a wonderful example of intelligent design commonly seen in the microbial world

The order-disorder transition of the (3x3)Sn/Ge(111) phase

Growing attention has been drawn in the past years to the \alpha-phase (1/3 monolayer) of Sn on Ge(111), which undergoes a transition from the low temperature (3x3) phase to the room temperature (\sqrt3 x \sqrt3)R30 one. On the basis of scanning tunnelling microscopy experiments, this transition was claimed to be the manifestation of a surface charge density wave (SCDW), i.e. a periodic redistribution of charge, possibly accompanied by a periodic lattice distortion, which determines a change of the surface symmetry. As further experiments with different techniques were being performed, increasing doubts were cast about the SCDW model. We have measured by He scattering the long range order of the 1/3 monolayer phase of Sn on the Ge(111) surface throughout the phase transition. The transition has been found of the order-disorder type with a critical temperature Tc=220 K. The expected 3-State Potts critical exponents are shown to be consistent with the observed power law dependence of the (3x3) order parameter and its correlation length close to Tc, thus excluding a charge density wave driven phase transition.Comment: 6 pages with 4 figures; updated reference

Effect of the dam’s feeding regimen on the meat quality of light suckling lambs

In order to verify the effect of the introduction of concentrates without GMO risk and at low aflatoxin risk in the diet of grazing milk ewes on the quanti-qualitative production of meat of their milk-fed light lambs, two trials were carried out - in Sicily, on 32 Comisana lambs, slaughtered at 49±4 days (trial 1); and in Sardinia, on 28 Sarda lambs, slaughtered at 31±4 days(trial 2) - comparing the following grazing dams’ feeding regimes: High stocking rate + Organic (barley – tickbean or pea) Concentrate (HO); High stocking rate + Conventional (maize-soybean) Concentrate (HC); Low stocking rate + Organic Concentrate (LO); Low stocking rate + Conventional Concentrate (LC). Lamb performances, carcass quality, meat colour and lipid content were not modified by dam’s feeding regimen. However, significant differences were observed in the fatty acid (FA) composition of the intramuscular fat of the older suckling lambs of trial 1. The main variation concerned n-3 polyunsaturated FAs and conjugated linoleic acids