Direct chargino–neutralino production at the LHC: interpreting the exclusion limits in the complex MSSM

We re-assess the exclusion limits on the parameters describing the supersymmetric (SUSY) electroweak sector of the MSSM obtained from the search for direct chargino–neutralino production at the LHC. We start from the published limits obtained for simplified models, where for the case of heavy sleptons the relevant branching ratio, $\mathrm {BR}(\tilde{\chi}^{0}_{2} \to \tilde{\chi}^{0}_{1} Z)$ , is set to one. We show how the decay mode $\tilde{\chi}^{0}_{2} \to \tilde{\chi}^{0}_{1} h$ , which cannot be neglected in any realistic model once kinematically allowed, substantially reduces the excluded parameter region. We analyze the dependence of the excluded regions on the phase of the gaugino soft SUSY-breaking mass parameter, M ₁, on the mass of the light scalar tau, $m_{{\tilde{\tau}_{1}}}$ , on tanβ as well as on the squark and slepton mass scales. Large reductions in the ranges of parameters excluded can be observed in all scenarios. The branching ratios of charginos and neutralinos are evaluated using a full NLO calculation for the complex MSSM. The size of the effects of the NLO calculation on the exclusion bounds is investigated. We furthermore assess the potential reach of the experimental analyses after collecting 100 fb^?1 at the LHC running at 13 TeV.     

A heterotic N=2 string with space–time supersymmetry

We reconsider the issue of embedding space–time fermions into the four-dimensional N=2 worldsheet supersymmetric string. A new heterotic theory is constructed, taking the right-movers from the N=4 topological extension of the conventional N=2 string but a c=0 conformal field theory supporting target-space supersymmetry for the left-moving sector. The global bosonic symmetry of the full formalism proves to be U(1,1), just as in the usual N=2 string. Quantization reveals a spectrum of only two physical states, one boson and one fermion, which fall in a multiplet of (1,0) supersymmetry.     

Energy–entropy competition and the effectiveness of stochastic gradient descent in machine learning

ABSTRACT

Finding parameters that minimise a loss function is at the core of many machine learning methods. The Stochastic Gradient Descent (SGD) algorithm is widely used and delivers state-of-the-art results for many problems. Nonetheless, SGD typically cannot find the global minimum, thus its empirical effectiveness is hitherto mysterious. We derive a correspondence between parameter inference and free energy minimisation in statistical physics. The degree of undersampling plays the role of temperature. Analogous to the energy–entropy competition in statistical physics, wide but shallow minima can be optimal if the system is undersampled, as is typical in many applications. Moreover, we show that the stochasticity in the algorithm has a non-trivial correlation structure which systematically biases it towards wide minima. We illustrate our argument with two prototypical models: image classification using deep learning and a linear neural network where we can analytically reveal the relationship between entropy and out-of-sample error.     

The role of machine learning method in the synthesis and biological ınvestigation of heterocyclic compounds

Molecular Diversity - Machine learning (ML) methods have attracted increasing interest in chemistry as in all fields of science in recent years. This method is of great importance for the design of...     

The extended conformal Einstein field equations with matter: The Einstein–Maxwell field

A discussion is given of the conformal Einstein field equations coupled with matter whose energy–momentum tensor is trace-free. These resulting equations are expressed in terms of a generic Weyl connection. The article shows how in the presence of matter it is possible to construct a conformal gauge which allows to know a priori the location of the conformal boundary. In vacuum this gauge reduces to the so-called conformal Gaussian gauge. These ideas are applied to obtain (i) a new proof of the stability of Einstein–Maxwell de Sitter-like spacetimes; (ii) a proof of the semi-global stability of purely radiative Einstein–Maxwell spacetimes.     

The Curie–Weiss model with Complex Temperature: Phase Transitions

We study the partition function of the Curie–Weiss model with complex temperature, and partially describe its phase transitions. As a consequence, we obtain information on the locations of zeros of the partition function (the Fisher zeros).     

Nonlinear Bethe–Heitler pair creation with attosecond laser pulses at the LHC

The creation of lepton pairs (e⁺e⁻$e^{+}{e}^{-}$ and μ⁺μ⁻${\mu }^{+}{\mu }^{-}$) via multiphoton absorption in collisions of ultrarelativistic ion beams with ultrashort high-frequency laser pulses is considered. Both the free and the bound-free production channels are addressed, where in the latter case the negatively charged lepton is created in a bound atomic state. It is shown that these nonlinear QED processes are observable when a table-top source of intense xuv or X-ray laser radiation is operated in conjunction with the LHC. We discuss the relative effectiveness of protons versus Pb ions and specify for each pair production channel the most suitable collision system.     

The optical responsivity in IR-photodetector based on armchair graphene nanoribbons with p–i–n structure

Armchair graphene nanoribbons (A-GNRs) are an alternative material to use in novel infrared photodetectors, because of their tunable energy gap in the infrared spectrum, and their high quantum efficiency. In this paper, an A-GNR p–i–n structure with all three structural families, different width, and different number of layers to use in IR detectors have been investigated. With calculating the band structure and energy gap using the tight-binding model and by including the edge deformation, the optical absorption in the single electron approximation has been obtained by calculating the optical conductance. Finally, we have calculated the quantum efficiency and the optical responsivity of A-GNR based IR photodetector as a function of incident photon energy, temperature, nanoribbon width and the number of layers. Results show that the responsivity of the A-GNR based IR photodetector increase by increasing the width and number of layers and decrease by increasing the temperature.     

The nuclear pore complex: biochemical machine or Maxwell demon?

The nuclear pore complex sits as the gateway between the genomic, nuclear environment and the primarily enzymatic realm of the cytoplasm. Large channels traversing the two membranes of the nuclear envelope, the nuclear pores govern the passage of specific molecules between these two major compartments of the cell. Its ability to limit passage to specific molecules, and furthermore to pump them against a gradient in concentration, raises intriguing physical questions. This article reviews basic aspects of the structure and operation of this biochemical pump, whose thermodynamic cycle differs from that of conventional machines.     

The Cavity of a Laser with an Interferential–Polarizational Filter Based on Phase Interferometers

Optics and Spectroscopy - It is proposed to use the phase properties of a reflective interferometer upon oblique incidence for spectral selection in lasers. The effect is achieved due to the...     

Theoretical predictions on α-decay properties of some unknown neutron-deficient actinide nuclei using machine learning

Neutron-deficient actinide nuclei provide a valuable window to probe heavy nuclear systems with large proton-neutron ratios. In recent years, several new neutron-deficient Uranium and Neptunium isotopes have been observed using α-decay spectroscopy [Z. Y. Zhang et al., Phys. Rev. Lett. 122, 192503 (2019); L. Ma et al., Phys. Rev. Lett. 125, 032502 (2020); Z. Y. Zhang et al., Phys. Rev. Lett. 126, 152502 (2021)]. In spite of these achievements, some neutron-deficient key nuclei in this mass region are still unknown in experiments. Machine learning algorithms have been applied successfully in different branches of modern physics. It is interesting to explore their applicability in α-decay studies. In this work, we propose a new model to predict the α-decay energies and half-lives within the framework based on a machine learning algorithm called the Gaussian process. We first calculate the α-decay properties of the new actinide nucleus \begin{document}$ {}^{214}{\rm{U}}$\end{document}. The theoretical results show good agreement with the latest experimental data, which demonstrates the reliability of our model. We further use the model to predict the α-decay properties of some unknown neutron-deficient actinide isotopes and compare the results with traditional models. The results may be useful for future synthesis and identification of these unknown isotopes.     

Addendum to: Search for anomalous top–gluon couplings at LHC revisited

In our latest paper “Search for anomalous top–gluon couplings at LHC revisited” in Eur. Phys. J. C 65 (2010), 127–135 (arXiv:0910.3049 [hep-ph]), we studied possible effects of nonstandard top–gluon couplings through the chromoelectric and chromomagnetic moments of the top quark using the total cross section of \(p\bar{p}/pp\to t\bar{t}X\) at Tevatron/LHC. There we pointed out that LHC data could give a stronger constraint on them, which would be hard to obtain from Tevatron data alone. We show here that the first CMS measurement of this cross section actually makes it possible.     

The Einstein–Dirac equation on Sasakian 3-manifolds

We prove that a Sasakian 3-manifold admitting a non-trivial solution to the Einstein–Dirac equation has necessarily constant scalar curvature. In the case when this scalar curvature is non-zero, their classification follows then from a result by Th. Friedrich and E.C. Kim. We also prove that a scalar-flat Sasakian 3-manifold admits no local Einstein spinors.     

The Electronic State of Flavoproteins: Investigations with Proton Electron–Nuclear Double Resonance

Electron–nuclear double resonance (ENDOR) spectroscopy provides useful information on hyperfine interactions between nuclear magnetic moments and the magnetic moment of an unpaired electron spin. Because the hyperfine coupling constant reacts quite sensitively to polarity changes in the direct vicinity of the nucleus under consideration, ENDOR spectroscopy can be favorably used for the detection of subtle protein–cofactor interactions. A number of pulsed ENDOR studies on flavoproteins have been published during the past few years; most of them were designed to characterize the flavin cofactor by means of its protonation state, or to detect individual protein–cofactor interactions. The aim of this study is to compare the pulsed ENDOR spectra from different flavoproteins in terms of variations of characteristic proton hyperfine values. The general concept is to observe limits of possible influences on the cofactor’s electronic state by surrounding amino acids. Furthermore, we compare ENDOR data obtained from in vivo experiments with in vitro data to emphasize the potential of the method for gaining molecular information in complex media.     

Investigations of the Drell–Yan process at the LHC: Results and prospects

Experimental results on the Drell–Yan process obtained with the CMS detector in the first run of the Large Hadron Collider are briefly reviewed. Some original results on this process are presented, and the prospects for its further investigations in the second LHC run are analyzed.     

LETTER: A Remark on Brans–Dicke Cosmological Dust Solutions with Negative ω

Analysing the Brans–Dicke solutions for the dust phase, we show that, for negative values of , they contain scenarios that display an initial subluminal expansion followed by an inflationary phase. This is due to a repulsive cosmic effect. We discuss these solutions with respect to the results of the observation of high redshift supernova as well as the age problem and structure formation. We establish possible connections of these solutions with those emerging from string effective models.