9 research outputs found
The Dark Side of Electroweak Naturalness Beyond the MSSM
Weak scale supersymmetry (SUSY) remains a prime explanation for the radiative
stability of the Higgs field. A natural account of the Higgs boson mass,
however, strongly favors extensions of the Minimal Supersymmetric Standard
Model (MSSM). A plausible option is to introduce a new supersymmetric sector
coupled to the MSSM Higgs fields, whose associated states resolve the little
hierarchy problem between the third generation squark masses and the weak
scale. SUSY also accomodates a weakly interacting cold dark matter (DM)
candidate in the form of a stable neutralino. In minimal realizations, the
thus-far null results of direct DM searches, along with the DM relic abundance
constraint, introduce a level of fine-tuning as severe as the one due to the
SUSY little hierarchy problem. We analyse the generic implications of new SUSY
sectors parametrically heavier than the minimal SUSY spectrum, devised to
increase the Higgs boson mass, on this little neutralino DM problem. We focus
on the SUSY operator of smallest scaling dimension in an effective field theory
description, which modifies the Higgs and DM sectors in a correlated manner.
Within this framework, we show that recent null results from the LUX experiment
imply a tree-level fine-tuning for gaugino DM which is parametrically at least
a few times larger than that of the MSSM. Higgsino DM whose relic abundance is
generated through a thermal freeze-out mechanism remains also severely
fine-tuned, unless the DM lies below the weak boson pair-production threshold.
As in the MSSM, well-tempered gaugino-Higgsino DM is strongly disfavored by
present direct detection results.Comment: 41 pages, 8 figures, references adde
Extraordinary Phenomenology from Warped Flavor Triviality
Anarchic warped extra dimensional models provide a solution to the hierarchy
problem. They can also account for the observed flavor hierarchies, but only at
the expense of little hierarchy and CP problems, which naturally require a
Kaluza-Klein (KK) scale beyond the LHC reach. We have recently shown that when
flavor issues are decoupled, and assumed to be solved by UV physics, the
framework's parameter space greatly opens. Given the possibility of a lower KK
scale and composite light quarks, this class of flavor triviality models enjoys
a rather exceptional phenomenology, which is the focus of this letter. We also
revisit the anarchic RS EDM problem, which requires m_{KK} > 8 TeV, and show
that it is solved within flavor triviality models. Interestingly, our framework
can induce a sizable differential t \bar{t} forward-backward asymmetry, and
leads to an excess of massive boosted di-jet events, which may be linked to the
recent findings of the CDF collaboration. This feature may be observed by
looking at the corresponding planar flow distribution, which is presented here.
Finally we point out that the celebrated standard model preference towards a
light Higgs is significantly reduced within our framework.Comment: 6 pages, 3 figures. Updated the EDM bound on the anarchic scenario;
extended discussion on the KK gluon's width, discovery potential and
resulting dijet signal; matches published versio
CP violation Beyond the MSSM: Baryogenesis and Electric Dipole Moments
We study electroweak baryogenesis and electric dipole moments in the presence
of the two leading-order, non-renormalizable operators in the Higgs sector of
the MSSM. Significant qualitative and quantitative differences from MSSM
baryogenesis arise due to the presence of new CP-violating phases and to the
relaxation of constraints on the supersymmetric spectrum (in particular, both
stops can be light). We find: (1) spontaneous baryogenesis, driven by a change
in the phase of the Higgs vevs across the bubble wall, becomes possible; (2)
the top and stop CP-violating sources can become effective; (3) baryogenesis is
viable in larger parts of parameter space, alleviating the well-known
fine-tuning associated with MSSM baryogenesis. Nevertheless, electric dipole
moments should be measured if experimental sensitivities are improved by about
one order of magnitude.Comment: 33 pages, 6 figure
The CXCL12Îł Chemokine Displays Unprecedented Structural and Functional Properties that Make It a Paradigm of Chemoattractant Proteins
The CXCL12γ chemokine arises by alternative splicing from Cxcl12, an essential gene during development. This protein binds CXCR4 and displays an exceptional degree of conservation (99%) in mammals. CXCL12γ is formed by a protein core shared by all CXCL12 isoforms, extended by a highly cationic carboxy-terminal (C-ter) domain that encompass four overlapped BBXB heparan sulfate (HS)-binding motifs. We hypothesize that this unusual domain could critically determine the biological properties of CXCL12γ through its interaction to, and regulation by extracellular glycosaminoglycans (GAG) and HS in particular. By both RT-PCR and immunohistochemistry, we mapped the localization of CXCL12γ both in mouse and human tissues, where it showed discrete differential expression. As an unprecedented feature among chemokines, the secreted CXCL12γ strongly interacted with cell membrane GAG, thus remaining mostly adsorbed on the plasmatic membrane upon secretion. Affinity chromatography and surface plasmon resonance allowed us to determine for CXCL12γ one of the higher affinity for HS (Kd = 0.9 nM) ever reported for a protein. This property relies in the presence of four canonical HS-binding sites located at the C-ter domain but requires the collaboration of a HS-binding site located in the core of the protein. Interestingly, and despite reduced agonist potency on CXCR4, the sustained binding of CXCL12γ to HS enabled it to promote in vivo intraperitoneal leukocyte accumulation and angiogenesis in matrigel plugs with much higher efficiency than CXCL12α. In good agreement, mutant CXCL12γ chemokines selectively devoid of HS-binding capacity failed to promote in vivo significant cell recruitment. We conclude that CXCL12γ features unique structural and functional properties among chemokines which rely on the presence of a distinctive C-ter domain. The unsurpassed capacity to bind to HS on the extracellular matrix would make CXCL12γ the paradigm of haptotactic proteins, which regulate essential homeostatic functions by promoting directional migration and selective tissue homing of cells
Molecular rules for chemo- and regio-selectivity of Candida antarctica lipase B in peptide acylation reactions
International audienceThe chemo- and regio-selectivity of the lipase B of Candida antarctica (CALB) in peptide acylation by oleic acid was investigated combining experimental and theoretical methodologies. Molecular dynamics and docking simulations were performed to study the selectivity of CALB toward the dipeptide Lysine-Serine at the molecular level. To this end, a model that mimics the acyl-enzyme system was built from CALB crystallographic structure and optimized then to be used as docking target. One main orientation of the peptide within the catalytic cavity was obtained. The lysine side chain was observed to enter the cavity, placing the s-amino group as to be acylated near the catalytic residues. This result was consistent with the N-acylation experimentally observed, showing the robustness of the model. Docking simulations were then applied to the peptides Lysine-Tyrosine-Serine, Serine-Tyrosine-Lysine and Leucine-GlutamineLysine-Tryptophan aiming to predict the selectivity of the reaction. Whatever the peptidic sequence and its constitutive amino acids, the models suggested the preferential N-acylation of the lysine side chain. These theoretical results were in perfect accordance with experimental data showing that Ns-oleoyl-Lys derivatives were the major products