Global well-posedness for the dynamical Q-tensor model of liquid crystals

In this paper, we consider a complex fluid modeling nematic liquid crystal flows, which is described by a system coupling Navier-Stokes equations with a parabolic Q-tensor system. We first prove the global existence of weak solutions in dimension three. Furthermore, the global well-posedness of strong solutions is studied with sufficiently large viscosity of fluid. Finally, we show a continuous dependence result on the initial data which directly yields the weak-strong uniqueness of solutions

Beyond Minimal Lepton Flavored Dark Matter

We consider a class of flavored dark matter (DM) theories where dark matter interacts with the Standard Model lepton fields at the renormalizable level. We allow for a general coupling matrix between the dark matter and leptons whose structure is beyond the one permitted by the minimal flavor violation (MFV) assumption. It is assumed that this is the only new source of flavor violation in addition to the Standard Model (SM) Yukawa interactions. The setup can be described by augmenting the SM flavor symmetry by an additional $\mathrm{SU}(3)_{\chi}$, under which the dark matter $\chi$ transforms. This framework is especially phenomenologically rich, due to possible novel flavor-changing interactions which are not present within the more restrictive MFV framework. As a representative case study of this setting, which we call "beyond MFV" (BMFV), we consider Dirac fermion dark matter which transforms as a singlet under the SM gauge group and a triplet under $\mathrm{SU}(3)_{\chi}$. The DM fermion couples to the SM lepton sector through a scalar mediator $\phi$. Unlike the case of quark-flavored DM, we show that there is no $\mathbb{Z}_3$ symmetry within either the MFV or BMFV settings which automatically stabilizes the lepton-flavored DM. We discuss constraints on this setup from flavor-changing processes, DM relic abundance as well as direct and indirect detections. We find that relatively large flavor-changing couplings are possible, while the dark matter mass is still within the phenomenologically interesting region below the TeV scale. Collider signatures which can be potentially searched for at the lepton and hadron colliders are discussed. Finally, we discuss the implications for decaying dark matter, which can appear if an additional stabilizing symmetry is not imposed.Comment: 30 pages, 12 figures; minor corrections, added references and discussion on decaying dark matter, matches published versio

Collisions of Jets of Particles from Active Galactic Nuclei with Neutralino Dark Matter

We examine the possibility that energetic Standard Model particles contained in the jets produced by active galactic nuclei (AGN) may scatter off of the dark matter halo which is expected to surround the AGN. In particular, if there are nearby states in the dark sector which can appear resonantly in the scattering, the cross section can be enhanced and a distinctive edge feature in the energy spectrum may appear. We examine bounds on supersymmetric models which may be obtained from the Fermi Gamma-ray Space Telescope observation of the nearby AGN Centaurus A.Comment: 20 pages, 9 figures; v2: version published in JCA

Theoretical and experimental investigation of ultrasonic wave propagation in suspensions of particles: effects of concentration and polymer modification

Ultrasound has been used as a Non-Destructive Testing method for colloids for characterising or monitoring purposes. The principle of ultrasound characterisation is based on measurements of ultrasound propagation in the tested sample, followed by interpretation of the experimental data using scattering models. One of the commonly used models is the single scattering model of Epstein and Carhart and Allegra and Hawley, which is often combined with the multiple scattering approach developed by Lloyd and Berry to account for the particle interactions in the acoustic field. These models have proved successful in application to dilute colloidal systems, but they are known to break down in highly concentrated systems due to non-acoustic field interactions. There are also situations where the particles to be characterised have unusual structures, such as hybrid particles with polymer modification on their surface. These particles have growing interest due to the potential application of their smart surface . The core-shell model by Anson and Chivers, has been shown to have some success in predicting the ultrasonic behaviour of such particles. However, the original core-shell model is a complicated model, which can be ill-conditioned under certain conditions and therefore limiting the application of this model. In order to address the issues above, the primary aim of this research was to develop and validate models for ultrasonic propagation in concentrated nano-suspensions and suspensions of particles modified with polymers. The limits of applicability of the classic ECAH/LB model for highly concentrated suspensions in the nano-scale was explored experimentally. The new model developed by Forrester and Pinfield was studied as a solution to interpret shear interactions between particles in concentrated suspensions. An analytical approximation was derived for the core-shell model and validated. The analytical solution was compared both analytically and numerically with Anson and Chivers full matrix model and the ECAH model. The possibility of applying the ultrasonic technique to core-shell nano-particles was investigated, and the core-shell model was validated experimentally with polymer-modified particle suspensions

Photon-tagged and B-meson-tagged b-jet production at the LHC

Tagged jet measurements in high energy hadronic and nuclear reactions provide constraints on the energy and parton flavor origin of the parton shower that recoils against the tagging particle. Such additional insight can be especially beneficial in illuminating the mechanisms of heavy flavor production in proton-proton collisions at the LHC and their modification in the heavy ion environment, which are not fully understood. With this motivation, we present theoretical results for isolated-photon-tagged and B-meson-tagged b-jet production at center-of-mass energy 5.1 TeV for comparison to the upcoming lead-lead data. We find that photon-tagged b-jets exhibit smaller momentum imbalance shift in nuclear matter, and correspondingly smaller energy loss, than photon-tagged light flavor jets. Our results show that B-meson tagging is most effective in ensuring that the dominant fraction of recoiling jets originate from prompt b-quarks. Interestingly, in this channel the large suppression of the cross section is not accompanied by a significant momentum imbalance shift.Comment: 9 pages, 6 figures, 1 table; typos in text fixed, extended discussion adde