Restoration Of Unitarity Research Articles

Comparing traditional and deep-learning techniques of kinematic reconstruction for polarization discrimination in vector boson scattering

Measuring longitudinally polarized vector boson scattering in mathrm {WW} channel is a promising way to investigate unitarity restoration with the Higgs mechanism and to search for possible physics beyond the Standard Model. In order to perform such a measurement, it is crucial to develop an efficient reconstruction of the full mathrm {W} boson kinematics in leptonic decays with the focus on polarization measurements. We investigated several approaches, from traditional ones up to advanced deep neural network structures, and we compared their abilities in reconstructing the mathrm {W} boson reference frame and in consequently measuring the longitudinal fraction mathrm {W}_{text {L}} in both semi-leptonic and fully-leptonic mathrm {WW} decay channels.

Polarization fraction measurement in ZZ scattering using deep learning

Measuring longitudinally polarized vector boson scattering in the ZZ channel is a promising way to investigate unitarity restoration with the Higgs mechanism and to search for possible new physics. We investigated several deep neural network structures and compared their ability to improve the measurement of the longitudinal fraction Z_L Z_L. Using fast simulation with the Delphes framework, a clear improvement is found using a previously investigated 'particle-based' deep neural network on a preprocessed dataset and applying principle component analysis to the outputs.A significance of around 1.7 standard deviations can be achieved with the integrated luminosity of 3000 fb-1 that will be recorded at the High-Luminosity LHC.

On unitarity of the particle–hole dispersive optical model

For the recently developed particle–hole dispersive optical model, weak violations of unitarity due to a phenomenological description of the spreading effect are considered. Methods for unitarity restoration are proposed and implemented for the 208Pb nucleus in the description of the energy-averaged isoscalar monopole double transition density and strength functions in a wide excitation energy interval that includes the isoscalar giant monopole resonance and its overtone. To illustrate abilities of the model, direct neutron decay of the mentioned giant resonance is also considered.

Continuum limit of overlap valence quarks on a twisted mass sea

We study a lattice QCD mixed action with overlap valence quarks on two flavours of Wilson maximally twisted mass sea quarks. Employing three different matching conditions to relate both actions to each other, we investigate the continuum limit by using three values of the lattice spacing ranging from a ≈ 0.05 fm to 0.08 fm . A particular emphasis is put on the effect on physical observables of the topological zero modes appearing in the valence overlap operator. We estimate the region of parameter space where the contribution from these zero modes is sufficiently small such that their effects can be safely controlled and a restoration of unitarity of the mixed action in the continuum limit is reached.

Describing neutrino oscillations in matter with Magnus expansion

We present new formalism for description of the neutrino oscillations in matter with varying density. The formalism is based on the Magnus expansion and has a virtue that the unitarity of the S-matrix is maintained in each order of perturbation theory. We show that the Magnus expansion provides better convergence of series: the restoration of unitarity leads to smaller deviations from the exact results especially in the regions of large transition probabilities. Various expansions are obtained depending on a basis of neutrino states and a way one splits the Hamiltonian into the self-commuting and non-commuting parts. In particular, we develop the Magnus expansion for the adiabatic perturbation theory which gives the best approximation. We apply the formalism to the neutrino oscillations in matter of the Earth and show that for the solar oscillation parameters the second order Magnus adiabatic expansion has better than 1% accuracy for all energies and trajectories. For the atmospheric Δ m 2 and small 1–3 mixing the approximation works well (<3% accuracy for sin 2 θ 13 = 0.01 ) outside the resonance region 2.7–8 GeV.

Deciphering the spin of new resonances in Higgsless models

We study the potential of the CERN large hadron collider to probe the spin of new massive vector boson resonances predicted by Higgsless models. We consider its production via weak boson fusion which relies only on the coupling between the new resonances and the weak gauge bosons. We show that the large hadron collider will be able to unravel the spin of the particles associated with the partial restoration of unitarity in vector boson scattering for integrated luminosities of $150--560\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$, depending on the new state mass and on the method used in the analyses.

Collider Phenomenology of the Higgsless Models

We identify and study the signatures of the recently proposed Higgsless models at the CERN Large Hadron Collider (LHC). We concentrate on tests of the mechanism of partial unitarity restoration in the longitudinal vector boson scattering, which is crucial to the phenomenological success of any Higgsless model and does not depend on the model-building details. We investigate the discovery reach for charged massive vector boson resonances and show that all of the preferred parameter space will be probed with 100 fb(-1) of LHC data. Unitarity restoration requires that the masses and couplings of the resonances obey certain sum rules. We discuss the prospects for their experimental verification at the LHC.

Unitarity restoration in the presence of closed timelike curves.

A proposal is made for a mathematically unambiguous treatment of evolution in the presence of closed timelike curves. In constrast to other proposals for handling the naively nonunitary evolution that is often present in such situations, this proposal is causal, linear in the initial density matrix and preserves probability. It provides a physically reasonable interpretation of invertible nonunitary evolution by redefining the final Hilbert space so that the evolution is unitary or equivalently by removing the nonunitary part of the evolution operator using a polar decomposition.

Non-perturbative effects in QED with chemical potential

Two non-perturbative phenomena are pointed out for the homogeneous electron gas. There is an O(1) uncertainty near the Fermi surface in determining the renormalized charge at metallic densities. Violation to the unitarity is found in Coulomb scattering, and it is conjectured that the restoration of unitarity involves formation of Cooper pairs and superconducting ground state.

Instanton-induced amplitudes in a supersymmetric theory

We consider the effective lagrangian for multiple self-interaction of matter fields induced by instantons in a weakly coupled SU (2) supersymmetric Yang-Mills theory with one matter flavor. By using the supersymmetric instanton calculus, we come to the surprising conclusion that the interaction induced by instantons in the one instanton sector of the theory is strictly local for scalar particle emission, accompanied by fermion number violation. The contribution of instantons arises only from instantons of zero scale size. The restoration of unitarity in high-energy scattering is thus only possible through multi-instanton-antiinstanton effects.

Unitarity restoration in the multi-instanton process

The instanton induced multi-particle scattering amplitude is considered in the scalar sector of standard electroweak theory. The Feynman diagram expansion is obtained, where the internal lines come from the interaction between instantons and/or anti-instantons. The resulting amplitude is manifestly unitary. An example of the unitary amplitude is obtained using the K-matrix formalism.

Extended Becchi-Rouet-Stora invariance for gravity via localOSp(42)supersymmetry

The supersymmetry $\mathrm{OSp}(\frac{4}{2})$ provides a natural classification group for gauge fields and their fictitious partners, needed for gauge fixing and restoration of unitarity. When the gravitational field and its adjuncts are so treated, with appropriate geometrical restrictions on the geometry of the superspace, a natural extended Becchi-Rouet-Stora (BRS) symmetry emerges for gravity in which the ghosts appear on an equal footing. The resulting action, invariant under gravitational BRS transformations and their duals, differs from the conventional asymmetric form. The validity of the new BRS identities is verified at the tree and one-loop levels.

Renormalizable asymtotically free quantum theory of gravity

We prove that quantum gravity with a quadratic lagrangian of a general type is asymptotically free in all essential coupling constants (including the effective λ-term). One-loop counter terms are obtained and asymptotic freedom is established also in conformally-invariant theories. We discuss the possibility of a ultra-macroscopic radius of confinement of ghosts, the restoration of unitarity due to radiative corrections and propose also the interaction with gravity leads to asymptotic freedom for the effective masses and all coupling constants in grand unified gauge theories.