Journals
2014 EN
Giulia Cusin · Jacopo Fumagalli · Michele Maggiore
We study the ghost-free bimetric theory of Hassan and Rosen, with parameters$\beta_i$ such that a flat Minkowski solution exists for both metrics. We showthat, expanding around this solution and eliminating one of the two metricswith its own equation of motion, the remaining metric is governed by theEinstein-Hilbert action plus a non-local term proportional to$W_{\mu\nu\rho\sigma} (\Box-m^2)^{-1}W^{\mu\nu\rho\sigma}$, where$W_{\mu\nu\rho\sigma}$ is the Weyl tensor. The result is valid to quadraticorder in the metric perturbation and to all orders in the derivative expansion.This example shows, in a simple setting, how such non-local extensions of GRcan emerge from an underlying consistent theory, at the purely classical level.
Journals
2014 EN
Gabriel Lopes Cardoso · Michele Cirafici · Suresh Nampuri
In this note, we employ indefinite theta functions to regularize canonical partition functions for single-center dyonic BPS black holes. These partition functions count dyonic degeneracies in the Hilbert space of four-dimensional toroidally compactified heterotic string theory, graded by electric and magnetic charges. The regularization is achieved by viewing the weighted sums of degeneracies as sums over charge excitations in the near-horizon attractor geometry of an arbitrarily chosen black hole background, and eliminating the unstable modes. This enables us to rewrite these sums in terms of indefinite theta functions. Background independence is then implemented by using the transformation property of indefinite theta functions under elliptic transformations, while modular transformations are used to make contact with semi-classical results in supergravity
Journals
2014 EN
Michele Redi · Andreas Weiler
The flavor protection in composite Higgs models with partial compositeness isknown to be insufficient. We explore the possibility to alleviate the tensionwith CP odd observables by assuming that flavor or CP are symmetries of thecomposite sector, broken by the coupling to Standard Model fields. Onerealization is that the composite sector has a flavor symmetry SU(3) or SU(3)_Ux SU(3)_D which allows us to realize Minimal Flavor Violation. We show how toavoid the previously problematic tension between a flavor symmetric compositesector and electro-weak precision tests. Some of the light quarks aresubstantially or even fully composite with striking signals at the LHC. Wediscuss the constraints from recent dijet mass measurements and give an outlookon the discovery potential. We also present a different protection mechanismwhere we separate the generation of flavor hierarchies and the origin of CPviolation. This can eliminate or safely reduce unwanted CP violating effects,realizing effectively "Minimal CP Violation" and is compatible with a dynamicalgeneration of flavor at low scales.
Journals
2014 EN
Michele Papucci · Alessandro Vichi · Kathryn M. Zurek
Monojet searches using Effective Field Theory (EFT) operators are usuallyinterpreted as a robust and model independent constraint on direct detection(DD) scattering cross-sections. At the same time, a mediator particle must bepresent to produce the dark matter (DM) at the LHC. This mediator particle maybe produced on shell, so that direct searches for the mediating particle canconstrain the effective operator being applied to monojet constraints. In thisfirst paper, we do a case study on t-channel models in monojet searches, wherethe (Standard Model singlet) DM is pair produced via a t-channel mediatingparticle, whose supersymmetric analogue is the squark. We compare monojetconstraints to direct constraints on single or pair production of the mediatorfrom multi-jets plus missing energy searches and we identify the regions wherethe latter dominate over the former. We show that computing bounds usingsupersymmetric simplified models and in the narrow width approximation, as donein previous work in the literature, misses important quantitative effects. Weperform a full event simulation and statistical analysis, and we compute theeffects of both on- and off-shell production of the mediating particle, showingthat for both the monojet and multi-jets plus missing energy searches,previously derived bounds provided more conservative bounds than what can beextracted by including all relevant processes in the simulation. Monojets andsearches for supersymmetry (SUSY) provide comparable bounds on a wide range ofthe parameter space, with SUSY searches usually providing stronger bounds,except in the regions where the DM particle and the mediator are very massdegenerate. The EFT approximation rarely is able to reproduce the actuallimits. In a second paper to follow, we consider the case of s-channelmediators.
Journals
2014 EN
M. C. Gonzalez-Garcia · Michele Maltoni · Thomas Schwetz
We present a global analysis of solar, atmospheric, reactor and acceleratorneutrino data in the framework of three-neutrino oscillations based on dataavailable in summer 2014. We provide the allowed ranges of the six oscillationparameters and show that their determination is stable with respect touncertainties related to reactor neutrino and solar neutrino flux predictions.We find that the maximal possible value of the Jarlskog invariant in the leptonsector is $0.0329 \pm 0.0009$ ($\pm 0.0027$) at the $1\sigma$ ($3\sigma$) leveland we use leptonic unitarity triangles to illustrate the ability of globaloscillation data to obtain information on CP violation. We discuss "tendenciesand tensions" of the global fit related to the octant of $\theta_{23}$ as wellas the CP violating phase $\delta_\mathrm{CP}$. The favored values of$\delta_\mathrm{CP}$ are around $3\pi/2$ while values around $\pi/2$ aredisfavored at about $\Delta\chi^2 \simeq 6$. We comment on the non-trivial taskto assign a confidence level to this $\Delta\chi^2$ value by performing a MonteCarlo study of T2K data.
Journals
2014 EN
Luis Aparicio · Michele Cicoli · Sven Krippendorf
+3 more
We analyse soft supersymmetry breaking in type IIB de Sitter string vacuaafter moduli stabilisation, focussing on models in which the Standard Model issequestered from the supersymmetry breaking sources and the spectrum ofsoft-terms is hierarchically smaller than the gravitino mass $m_{3/2}$. Due tothis feature, these models are compatible with gauge coupling unification andTeV scale supersymmetry with no cosmological moduli problem. We determine theinfluence on soft-terms of concrete realisations of de Sitter vacua constructedfrom supersymmetric effective actions. One of these scenarios provides thefirst study of soft-terms for consistent string models embedded in a compactCalabi-Yau manifold with all moduli stabilised. Depending on the modulidependence of the Kaehler metric for matter fields and on the mechanismresponsible to obtain a de Sitter vacuum, we find two scenarios forphenomenology: (i) a split-supersymmetry scenario where gaugino masses aresuppressed with respect to scalar masses: $M_{1/2} \sim m_{3/2} \epsilon \llm_0 \sim m_{3/2} \sqrt{\epsilon} \ll m_{3/2}$ for $\epsilon \sim m_{3/2}/M_P\ll 1$; (ii) a typical MSSM scenario where all soft-terms are of the sameorder: $M_{1/2} \sim m_0 \sim m_{3/2} \epsilon \ll m_{3/2}$. Background fluxesdetermine the numerical coefficients of the soft-terms allowing for smallvariations of parameters as is necessary to confront data and to interpolatebetween different scenarios. We comment on different stringy origins of themu-term and potential sources of desequestering.
Journals
2014 EN
Paola Manzotti · Michele Zucali · Michel Ballèvre
+2 more
International audienceThe Dent Blanche Tectonic System (DBTS) is a composite thrust sheet derived from the previously thinned passive Adriatic continental margin. A kilometric high-strain zone, the Roisan-Cignana Shear Zone (RCSZ) defines the major tectonic boundary within the DBTS and separates it into two subunits, the Dent Blanche s.s. nappe to the northwest and the Mont Mary nappe to the southeast. Within this shear zone, tectonic slices of Mesozoic and pre-Alpine meta-sediments became amalgamated with continental basement rocks of the Adriatic margin. The occurrence of high pressure assemblages along the contact between these tectonic slices indicates that the amalgamation occurred prior to or during the subduction process, at an early stage of the Alpine orogenic cycle. Detailed mapping, petrographic and structural analysis show that the Roisan-Cignana Shear Zone results from several superimposed Alpine structural and metamorphic stages. Subduction of the continental fragments is recorded by blueschist-facies deformation, whereas the Alpine collision is reflected by a greenschist facies overprint associated with the development of large-scale open folds. The post-nappe evolution comprises the development of low-angle brittle faults, followed by large-scale folding (Vanzone phase) and finally brittle extensional faults. The RCSZ shows that fragments of continental crust had been torn off the passive continental margin prior to continental collision, thus recording the entire history of the orogenic cycle. The role of preceding Permo-Triassic lithospheric thinning, Jurassic rifting, and ablative subduction processes in controlling the removal of crustal fragments from the reactivated passive continental margin is discussed. Results of this study constrain the temporal sequence of the tectono-metamorphic processes involved in the assembly of the DBTS, but they also show limits on the interpretation. In particular it remains difficult to judge to what extent pre-collisional rifting at the Adriatic continental margin preconditioned the efficiency of convergent processes, i.e. accretion, subduction, and orogenic exhumation
Journals
2014 EN
Paola Manzotti · Michel Ballèvre · Michele Zucali
+2 more
International audienceThis study reviews and synthesizes the presentknowledge on the Sesia–Dent Blanche nappes, the highesttectonic elements in the Western Alps (Switzerland andItaly), which comprise pieces of pre-Alpine basement andMesozoic cover. All of the available data are integrated in acrustal-scale kinematic model with the aim to reconstructthe Alpine tectono-metamorphic evolution of the Sesia–Dent Blanche nappes. Although major uncertainties remainin the pre-Alpine geometry, the basement and coversequences of the Sesia–Dent Blanche nappes are seen aspart of a thinned continental crust derived from the Adriaticmargin. The earliest stages of the Alpine evolution areinterpreted as recording late Cretaceous subduction of theAdria-derived Sesia–Dent Blanche nappes below theSouth-Alpine domain. During this subduction, severalsheets of crustal material were stacked and separated byshear zones that rework remnants of their Mesozoic cover.The recently described Roisan-Cignana Shear Zone of theDent Blanche Tectonic System represents such a shearzone, indicating that the Sesia–Dent Blanche nappes representa stack of several individual nappes. During thesubsequent subduction of the Piemonte–Liguria Oceanlarge-scale folding of the nappe stack (including the Roisan-Cignana Shear Zone) took place under greenschistfacies conditions, which indicates partial exhumation of theDent Blanche Tectonic System. The entrance of the Brianc¸onnais micro-continent within the subduction zone ledto a drastic change in the deformation pattern of the Alpinebelt, with rapid exhumation of the eclogite-facies ophiolitebearingunits and thrust propagation towards the foreland.Slab breakoff probably was responsible for allowing partialmelting in the mantle and Oligocene intrusions into themost internal parts of the Sesia–Dent Blanche nappes.Finally, indentation of the Adriatic plate into the orogenicwedge resulted in the formation of the Vanzone back-fold,which marks the end of the pervasive ductile deformationwithin the Sesia–Dent Blanche nappes during the earliestMiocene
Journals
2014 EN
Giuseppe Lupo · Michele Bertacchi · Nicoletta Carucci
+3 more
Embryonic stem cells (ESCs) have been used extensively as in vitro models of neural development and disease, with special efforts towards their conversion into forebrain progenitors and neurons. The forebrain is the most complex brain region, giving rise to several fundamental structures, such as the cerebral cortex, the hypothalamus, and the retina. Due to the multiplicity of signaling pathways playing different roles at distinct times of embryonic development, the specification and patterning of forebrain has been difficult to study in vivo. Research performed on ESCs in vitro has provided a large body of evidence to complement work in model organisms, but these studies have often been focused more on cell type production than on cell fate regulation. In this review, we systematically reassess the current literature in the field of forebrain development in mouse and human ESCs with a focus on the molecular mechanisms of early cell fate decisions, taking into consideration the specific culture conditions, exogenous and endogenous molecular cues as described in the original studies. The resulting model of early forebrain induction and patterning provides a useful framework for further studies aimed at reconstructing forebrain development in vitro for basic research or therapy.
Journals
2014 EN
Gaia Fabrizio · Simone Di Paola · Annalisa Stilla
+6 more
Protein mono-ADP-ribosylation is a reversible post-translational modification of cellular proteins. This scheme of amino-acid modification is used not only by bacterial toxins to attack host cells, but also by endogenous ADP-ribosyltransferases (ARTs) in mammalian cells. These latter ARTs include members of three different families of proteins: the well characterised arginine-specific ecto-enzymes (ARTCs), two sirtuins, and some members of the poly(ADP-ribose) polymerase (PARP/ARTD) family. In the present study, we demonstrate that human ARTC1 is localised to the endoplasmic reticulum (ER), in contrast to the previously characterised ARTC proteins, which are typical GPI-anchored ecto-enzymes. Moreover, using the "macro domain" cognitive binding module to identify ADP-ribosylated proteins, we show here that the ER luminal chaperone GRP78/BiP (glucose-regulated protein of 78 kDa/immunoglobulin heavy-chain-binding protein) is a cellular target of human ARTC1 and hamster ARTC2. We further developed a procedure to visualise ADP-ribosylated proteins using immunofluorescence. With this approach, in cells overexpressing ARTC1, we detected staining of the ER that co-localises with GRP78/BiP, thus confirming that this modification occurs in living cells. In line with the key role of GRP78/BiP in the ER stress response system, we provide evidence here that ARTC1 is activated during the ER stress response, which results in acute ADP-ribosylation of GRP78/BiP paralleling translational inhibition. Thus, this identification of ARTC1 as a regulator of GRP78/BiP defines a novel, previously unsuspected, player in GRP78-mediated ER stress responses.