A search is performed for a new sub-GeV vector boson (A′) mediated production of dark matter (χ) in the fixed-target experiment, NA64, at the CERN SPS. The A′, called dark photon, can be generated in ...the reaction e−Z→e−ZA′ of 100 GeV electrons dumped against an active target followed by its prompt invisible decay A′→χχ¯. The experimental signature of this process would be an event with an isolated electron and large missing energy in the detector. From the analysis of the data sample collected in 2016 corresponding to 4.3×1010 electrons on target no evidence of such a process has been found. New stringent constraints on the A′ mixing strength with photons, 10−5≲ε≲10−2, for the A′ mass range mA′≲1 GeV are derived. For models considering scalar and fermionic thermal dark matter interacting with the visible sector through the vector portal the 90% C.L. limits 10−11≲y≲10−6 on the dark-matter parameter y=ε2αD(mχmA′)4 are obtained for the dark coupling constant αD=0.5 and dark-matter masses 0.001≲mχ≲0.5 GeV. The lower limits αD≳10−3 for pseudo-Dirac dark matter in the mass region mχ≲0.05 GeV are more stringent than the corresponding bounds from beam dump experiments. The results are obtained by using exact tree level calculations of the A′ production cross sections, which turn out to be significantly smaller compared to the one obtained in the Weizsäcker-Williams approximation for the mass region mA′≳0.1 GeV.
Split NMSSM with electroweak baryogenesis Demidov, S. V.; Gorbunov, D. S.; Kirpichnikov, D. V.
The journal of high energy physics,
11/2016, Letnik:
2016, Številka:
11
Journal Article
Recenzirano
Odprti dostop
A
bstract
In light of the Higgs boson discovery and other results of the LHC we re-consider generation of the baryon asymmetry in the split Supersymmetry model with an additional singlet superfield ...in the Higgs sector (non-minimal split SUSY). We find that successful baryogenesis during the first order electroweak phase transition is possible within a phenomenologically viable part of the model parameter space. We discuss several phenomenological consequences of this scenario, namely, predictions for the electric dipole moments of electron and neutron and collider signatures of light charginos and neutralinos.
We discuss gravitational wave signal from the strongly first order electroweak phase transition in the split NMSSM. We find that for sets of parameters predicting successful electroweak baryogenesis ...the gravitational wave signal can be within the reach of future experiments LISA, BBO and Ultimate DECIGO.
The improved results on a direct search for a new X ( 16.7 MeV ) boson that could explain the anomalous excess of e+e− pairs observed in the decays of the excited 8Be ∗ nuclei ("Berillium or X17 ...anomaly") are reported. Interestingly, new recent results in the nuclear transitions of another nucleus, 4 He , seems to support this anomaly spurring the need for an independent measurement. If the X boson exists, it could be produced in the bremsstrahlung reaction e − Z → e − Z X by a high energy beam of electrons incident on the active target in the NA64 experiment at the CERN Super Proton Synchrotron and observed through its subsequent decay into e+e− pairs. No evidence for such decays was found from the combined analysis of the data samples with total statistics corresponding to 8.4 × 1010 electrons on target collected in 2017 and 2018. This allows one to set new limits on the X−e− coupling in the range 1.2 × 10−4 ≲ ε e ≲ 6.8 × 10−4 , excluding part of the parameter space favored by the X17 anomaly, and setting new bounds on the mixing strength of photons with dark photons ( A ′ ) with a mass ≲ 24 MeV . For the 2018 run, the setup was optimized to probe the region of parameter space characterized by a large coupling ε . This allowed a significant improvement in sensitivity despite a relatively modest increase in statistics.
We discuss the aspects of axion-like-particles searches with Light-Shining-through-Wall experimental setups consisted of two radio-frequency cavities. We compare the efficiencies of four setups which ...involve the cavity pump modes and external magnetic fields. Additionally, we discuss the sensitivity dependence both on the relative position of two cylindrical cavities and on their radius-to-length ratio.
Recently, it was revealed that tumor cells are significantly softer than normal cells. Although this phenomenon is well known, it is connected with many questions which are still unanswered. Among ...these questions are the molecular mechanisms which cause the change in stiffness and the correlation between cell mechanical properties and their metastatic potential. We studied mechanical properties of cells with different levels of cancer transformation. Transformed cells in three systems with different transformation types (monooncogenic N-RAS, viral and cells of tumor origin) were characterized according to their morphology, actin cytoskeleton and focal adhesion organization. Transformation led to reduction of cell spreading and thus decreasing the cell area, disorganization of actin cytoskeleton, lack of actin stress fibers and decline in the number and size of focal adhesions. These alterations manifested in a varying degree depending on type of transformation. Force spectroscopy by atomic force microscopy with spherical probes was carried out to measure the Young's modulus of cells. In all cases the Young's moduli were fitted well by log-normal distribution. All the transformed cell lines were found to be 40–80% softer than the corresponding normal ones. For the cell system with a low level of transformation the difference in stiffness was less pronounced than for the two other systems. This suggests that cell mechanical properties change upon transformation, and acquisition of invasive capabilities is accompanied by significant softening.
•Young's modulus of transformed and normal fibroblasts was measured by AFM.•The transformed cells were significantly softer than the control ones.•For cells with higher level of transformation the softening was more pronounced.•Log-normal distribution of the Young's modulus values was shown for all cell lines.
PDF
