50175 research outputs found
Sort by
Search for Leptoquarks Coupled to Third-Generation Quarks in Proton-Proton Collisions at root s=13 TeV
No full textThree of the most significant measured deviations from standard model predictions, the enhanced decay rate for B -> D-(*())tau nu, hints of lepton universality violation in B -> K-(*())ll decays, and the anomalous magnetic moment of the muon, can be explained by the existence of leptoquarks (LQs) with large couplings to third-generation quarks and masses at the TeV scale. The existence of these states can be probed at the LHC in high energy proton-proton collisions. A novel search is presented for pair production of LQs coupled to a top quark and a muon using data at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb(-1), recorded by the CMS experiment. No deviation from the standard model prediction has been observed and scalar LQs decaying exclusively into t mu are excluded up to masses of 1420 GeV. The results of this search are combined with those from previous searches for LQ decays into t tau and b nu, which excluded scalar LQs below masses of 900 and 1080 GeV. Vector LQs are excluded up to masses of 1190 GeV for all possible combinations of branching fractions to t mu, t tau and b nu. With this analysis, all relevant couplings of LQs with an electric charge of -1/3 to third-generation quarks are probed for the first time
Steady states of a quasiperiodically driven integrable system
No full textDriven many-body quantum systems where some parameter in the Hamiltonian is varied quasiperiodically in time may exhibit nonequilibrium steady states that are qualitatively different from their periodically driven counterparts. Here we consider a prototypical integrable spin system, the spin-1/2 transverse field Ising model in one dimension, in a pulsed magnetic field. The time dependence of the field is taken to be quasiperiodic by choosing the pulses to be of two types that alternate according to a Fibonacci sequence. We show that a steady state emerges after an exponentially long time when local properties (or equivalently, reduced density matrices of subsystems with size much smaller than the full system) are considered. We use the temporal evolution of certain coarse-grained quantities in momentum space to understand this nonequilibrium steady state in more detail and show that unlike the previously known cases, this steady state is neither described by a periodic generalized Gibbs ensemble nor by an infinite temperature ensemble. Finally, we study a toy problem with a single two-level system driven by a Fibonacci sequence; this problem shows how sensitive the nature of the final steady state is to the different parameters
Curvature inequalities for operators in the Cowen-Douglas class and localization of the Wallach set
No full textFor any bounded domain in C-m, let B-1() denote the Cowen-Douglas class of commuting m-tuples of bounded linear operators. For an m-tuple T in the Cowen-Douglas class B-1(), let N-T (w) denote the restriction of T to the subspace i,j=1m</mml:msubsup>ker(Ti-wiI)(Tj-wjI). This commuting m-tuple N-T (w) of m + 1 dimensional operators induces a homomorphism NT(w) of the polynomial ring Pz(1), <bold> </bold>, z(m)], namely, NT(w) (p) = p(N-T (w)), p Pz(1), <bold> </bold>, z(m)]. We study the contractivity and complete contractivity of the homomorphism NT(w). Starting from the homomorphism NT(w), we construct a natural class of homomorphisms N()(w), > 0, and relate the properties of N()(w) to those of NT(w). Explicit examples arising from the multiplication operators on the Bergman space of are investigated in detail. Finally, it is shown that contractive properties of NT(w) are equivalent to an inequality for the curvature of the Cowen-Douglas bundle E-T. However, we construct examples to show that the contractivity of the homomorphism (T) does not follow, even if <mml:msub>NT(w) is contractive for all w in
On the Polyakov-Mellin bootstrap
No full textWe elaborate on some general aspects of the crossing symmetric approach of Polyakov to the conformal bootstrap, as recently formulated in Mellin space. This approach uses, as building blocks, Witten diagrams in AdS. We show the necessity for having contact Witten diagrams, in addition to the exchange ones, in two different contexts: a) the large c expansion of the holographic bootstrap b) in the E expansion at subleading orders to the ones studied already. In doing so, we use alternate simplified representations of the Witten diagrams in Mellin space. This enables us to also obtain compact, explicit expressions (in terms of a F-7(6) hypergeometric function!) for the analogue of the crossing kernel for Witten diagrams i.e., the decomposition into s-channel partial waves of crossed channel exchange diagrams
Investigation of disorder in carbon encapsulated core-shell Fe/Fe3C nanoparticles synthesized by one-step pyrolysis
No full textFe/Fe3C (core) - graphite (shell) nanoparticles embedded in micron sized amorphous carbon globules were synthesized by pyrolysis route in a closed reactor. A large number of such nanoparticles were observed to be distributed in the inner section of each globule covered by amorphous carbon in the outer regions. The distribution of nanoparticles varies according to the reaction-temperature-profile of the furnace during the synthesis process. These particles catalyze the formation of the graphitic coating on their surface, due to metastable nature of Fe3C. The globules which contain smaller catalyst particles were found to contain defectiveand less amount of graphitic carbon and large amount of amorphous carbon. We observed that for low synthesis temperature conditions the globules contain a thicker shell of amorphous carbon (without any catalyst particle). Furthermore, the amount of disorder in the graphitic layer is determined by the number and size of the (Fe/Fe3C) catalyst particles and reaction-temperature. The disorder in the graphitic layer on the particles can be potentially important for the catalytic behaviour of these particles
Search for resonances in the mass spectrum of muon pairs produced in association with b quark jets in proton-proton collisions at
No full textA search for resonances in the mass range 12-70 GeV produced in association with a b quark jet and a second jet, and decaying to a muon pair, is reported. The analysis is based on data from proton-proton collisions at center-of-mass energies of 8 and 13 TeV, collected with the CMS detector at the LHC and corresponding to integrated luminosities of 19.7 and 35.9 fb(-1), respectively. The search is carried out in two mutually exclusive event categories. Events in the first category are required to have a b quark jet in the central region (|| 2.4) and at least one jet in the forward region (|| > 2.4). Events in the second category are required to have two jets in the central region, at least one of which is identified as a b quark jet, no jets in the forward region, and low missing transverse momentum. An excess of events above the background near a dimuon mass of 28 GeV is observed in the 8 TeV data, corresponding to local significances of 4.2 and 2.9 standard deviations for the first and second event categories, respectively. A similar analysis conducted with the 13 TeV data results in a mild excess over the background in the first event category corresponding to a local significance of 2.0 standard deviations, while the second category results in a 1.4 standard deviation deficit. The fiducial cross section measurements and 95% confidence level upper limits on those for a resonance consistent with the 8 TeV excess are provided at both collision energies
Seismic site classification and amplification of shallow bedrock sites
No full textThis study attempts to develop empirical correlations between average penetration resistance ((NSPT-R) over bar), averaged velocities over depth up to bedrock depth ((VS-R) over bar) and 30 m ((V-S30) over bar) for shallow depth sites (having bedrock at a depth less than 25 m). A total of 63 shallow sites were assessed for penetration resistance values up to the bedrock from Standard Penetration Tests (SPT) and dynamic soil property analysis, i.e., Shear Wave Velocity (V-S) from Multichannel Analysis of Surface Waves. The study shows that 30 m averaged shear wave velocities are more than the average velocity up to bedrock depth in shallow bedrock sites because of inclusion of rock site velocity. Furthermore, averaged SPT-N((NSPT-R) over bar) and average V-S ((VS-R) over bar) up to bedrock depth were correlated with the 30 m average((V-S30) over bar) values. This is the first attempt in developing empirical relationships of this kind for seismic site classification. These correlations can be made useful for seismic site classification of sites in regions with Standard Penetration Test (N-SPT) values and limited V-S values. Further surface and bedrock motion recordings of 12 selected KiK-net shallow depth sites were collected and amplifications were estimated with the respective peak ground acceleration, spectral acceleration and thereby related to the average shear wave velocity up to bedrock and 30 m. The results show that the amplification is better correlated to the (VS-R) over bar than (V-S30) over bar for shallow depth sites, and more data can be added to strengthen this correlation
Weighted norm inequalities for Weyl multipliers and fourier multipliers on the Heisenberg group
No full textIn this paper, we prove weighted norm inequalities for Weyl multipliers satisfying Mauceri's condition. As an application, we prove certain multiplier theorems on the Heisenberg group and also show, in the context of a theorem of Weis on operator-valued Fourier multipliers, that R-boundedness of the derivative of the multiplier is not necessary for boundedness of the multiplier transform
High Thermoelectric Figure of Merit via Tunable Valley Convergence Coupled Low Thermal Conductivity in A(II)B(IV)C(2)(V) Chalcopyrites
No full textDevelopment of efficient thermoelectric materials requires a designing approach that leads to excellent electronic and phononic transport properties. Using first-principles density functional theory and semiclassical Boltzmann transport theory, we report unprecedented enhancement in electronic transport properties of A(II)B(IV)C(2)(V) (group II = Be, Mg, Zn, and Cd; group IV = Si, Ge, and Sn; and group V = P and As) chalcopyrites via isoelectronic substitution. Multiple valleys in conduction bands, present in these compounds, are tuned to converge by substitution of group IV dopant. Additionally, this substitution improves the convergence of valence bands, which is found to have a direct correlation with the tetragonal distortion of these chalcopyrites. Furthermore, several chalcopyrite compounds with heavy elements such as Zn, Cd, and As possess low phonon group velocities and large Gruneisen parameters that lead to low lattice thermal conductivity. Combination of optimized electronic transport properties and low thermal conductivity results in maximum ZT of 1.67 in CdGeAs2 at moderate n-type doping. The approach developed here to enhance the thermoelectric efficiency can be generalized to other class of materials
The crystal structure of Mycobacterium tuberculosis high-temperature requirement A protein reveals an autoregulatory mechanism
No full textThe crystal structure of Mycobacterium tuberculosis high-temperature requirement A (HtrA) protein was determined at 1.83 angstrom resolution. This membrane-associated protease is essential for the survival of M. tuberculosis. The crystal structure reveals that interactions between the PDZ domain and the catalytic domain in HtrA lead to an inactive conformation. This finding is consistent with its proposed role as a regulatory protease that is conditionally activated upon appropriate environmental triggers. The structure provides a basis for directed studies to evaluate the role of this essential protein and the regulatory pathways that are influenced by this protease