Realistic Mass Research Articles

Finite isospin chiral perturbation theory in a magnetic field

The phase diagram of finite isospin, zero temperature QCD with the pions coupled to photons in a uniform external magnetic field is explored in the low field, small isospin density regime for which chiral perturbation theory is a valid description. For realistic pion masses, the system behaves as a type-II superconductor: a uniform superconducting state is formed at low-enough magnetic fields, a vortex state for intermediate magnetic fields and finally a normal state for large magnetic fields. In each these phases (including the vortex phase), the $\pi^{0}$ remains uncondensed just as in the zero-external field problem. The critical magnetic field where the phase transition from the uniform superconducting state to a vortex state occurs was found numerically.

Yukawa hierarchies at the point of E8 in F-theory

We analyse the structure of Yukawa couplings in local SU(5) F-theory models with $E_8$ enhancement. In this setting the $E_8$ symmetry is broken down to SU(5) by a 7-brane configuration described by T-branes, all the Yukawa couplings are generated in the vicinity of a point and only one family of quarks and leptons is massive at tree-level. The other two families obtain their masses when non-perturbative effects are taken into account, being hierarchically lighter than the third family. However, and contrary to previous results, we find that this hierarchy of fermion masses is not always appropriate to reproduce measured data. We find instead that different T-brane configurations breaking $E_8$ to SU(5) give rise to distinct hierarchical patterns for the holomorphic Yukawa couplings. Only some of these patterns allow to fit the observed fermion masses with reasonable local model parameter values, adding further constraints to the construction of F-theory GUTs. We consider an $E_8$ model where such appropriate hierarchy is realised and compute its physical Yukawas, showing that realistic charged fermions masses can indeed be obtained in this case.

Towards the equation of state of quark-gluon matter from lattice QCD with Wilson twisted mass fermions

This contribution gives an overview of a long-term study of quark-gluon matter under extreme conditions employing Euclidean lattice discretized Quantum Chromodynamics (QCD) with Wilson twisted mass fermions and improved gauge actions. The analysis relies on methods and results of the European Twisted Mass Collaboration at zero temperature. We will start for two mass-degenerate light flavour degrees of freedom with a thorough investigation of the three-dimensional phase diagram of the bare coupling and the two mass-related parameters. Then for the same case we are going to describe the search for the pseudo-critical behaviour at various quark mass values. We shall discuss the behaviour of the (pseudo-)critical temperature Tc as a function of the (charged) pion mass mπ and the difficulty to extract the chiral limit in order to establish or reject the conjectured O(4)-universality. For the two-flavour case we shall further present very recent results for the thermodynamic Equation of State at non-zero temperature. Finally we will provide a view on an ongoing first exploration of QCD thermodynamics under the inclusion of virtual strange and charm quarks at their realistic mass values.

Growing black holes and galaxies: black hole accretion versus star formation rate

We present a new suite of hydrodynamical simulations and use it to study, in detail, black hole and galaxy properties. The high time, spatial and mass resolution, and realistic orbits and mass ratios, down to 1:6 and 1:10, enable us to meaningfully compare star formation rate (SFR) and BH accretion rate (BHAR) timescales, temporal behaviour and relative magnitude. We find that (i) BHAR and galaxy-wide SFR are typically temporally uncorrelated, and have different variability timescales, except during the merger proper, lasting ~0.2-0.3 Gyr. BHAR and nuclear (<100 pc) SFR are better correlated, and their variability are similar. Averaging over time, the merger phase leads typically to an increase by a factor of a few in the BHAR/SFR ratio. (ii) BHAR and nuclear SFR are intrinsically proportional, but the correlation lessens if the long-term SFR is measured. (iii) Galaxies in the remnant phase are the ones most likely to be selected as systems dominated by an active galactic nucleus (AGN), because of the long time spent in this phase. (iv) The timescale over which a given diagnostic probes the SFR has a profound impact on the recovered correlations with BHAR, and on the interpretation of observational data.

Accidental symmetries and massless quarks in the economical 3-3-1 model

In the framework of a 3-3-1 model with a minimal scalar sector, known as the economical 3-3-1 model, we study its capabilities of generating realistic quark masses. After a detailed study of the symmetries of the model, before and after the spontaneous symmetry breaking, we find a remaining axial symmetry that prevents some quarks to gain mass at all orders in perturbation theory. Since this accidental symmetry is anomalous, we also consider briefly the possibility to generate their masses for non-perturbative effects. However, we find that non-perturbative effects are not enough to generate the measured masses for that three massless quarks. Hence, these results imply that the economical 3-3-1 model is not a realistic description of the electroweak interaction and it has to be modified.

Folding insensitive, high energy density lithium-ion battery featuring carbon nanotube current collectors

Here we report a fully foldable lithium-ion battery (LIB) with high energy density using Li4Ti5O12 (LTO) as the anode and LiCoO2 (LCO) as the cathode with free standing carbon nanotube (CNT) Macro-Films (CMF) as the current collectors. The CMFs were produced using a scalable Floating Catalyst Chemical Vapor Deposition method. The highly flexible CMFs could be folded multiple times without plastic deformation. Importantly the active material (LTO in case of the anode or LCO in case of the cathode) infiltrates into the pores of the CMF forming a strong interface that is resistant to delamination even when the battery is folded repeatedly. Not only does the CMF impart shape conformality it also significantly boosts the energy density of the device. This is because the CMF is significantly lighter than conventional metal current collectors. We show that the energy density of the fully foldable battery with CMF current collectors can be up to ∼2-fold higher than conventional LIBs at realistic mass loading (∼5mgcm−2) of the electrode materials.

The updated ESA Earth System Model for future gravity mission simulation studies

A new synthetic model of the time-variable global gravity field is now available based on realistic mass variability in atmosphere, oceans, terrestrial water storage, continental ice-sheets, and the solid Earth. The updated ESA Earth System Model is provided in Stokes coefficients up to degree and order 180 with a temporal resolution of 6 h covering the time period 1995–2006, and can be readily applied as a source model in future gravity mission simulation studies. The model contains plausible variability and trends in both low-degree coefficients and the global mean eustatic sea level. It depicts reasonable mass variability all over the globe at a wide range of frequencies including multi-year trends, year-to-year variability, and seasonal variability even at very fine spatial scales, which is important for a realistic representation of spatial aliasing and leakage. In particular on these small spatial scales between 50 and 250 km, the model contains a range of signals that have not been reliably observed yet by satellite gravimetry. In addition, the updated Earth System Model provides substantial high-frequency variability at periods down to a few hours only, thereby allowing to critically test strategies for the minimization of temporal aliasing.

Introduction of temporal sub-stepping in the Multi-Level Multi-Domain semi-implicit Particle-In-Cell code Parsek2D-MLMD

In this paper, the introduction of temporal sub-stepping in Multi-Level Multi-Domain (MLMD) simulations of plasmas is discussed. The MLMD method addresses the multi-scale nature of space plasmas by simulating a problem at different levels of resolution. A large-domain “coarse grid” is simulated with low resolution to capture large-scale, slow processes. Smaller scale, local processes are obtained through a “refined grid” which uses higher resolution. Very high jumps in the resolution used at the different levels can be achieved thanks to the Implicit Moment Method and appropriate grid interlocking operations. Up to now, the same time step was used at all the levels. Now, with temporal sub-stepping, the different levels can also benefit from the use of different temporal resolutions. This saves further resources with respect to “traditional” simulations done using the same spatial and temporal stepping on the entire domain. It also prevents the levels from working at the limits of the stability condition of the Implicit Moment Method. The temporal sub-stepping is tested with simulations of magnetic reconnection in space. It is shown that, thanks to the reduced costs of MLMD simulations with respect to single-level simulations, it becomes possible to verify with realistic mass ratios scaling laws previously verified only for reduced mass ratios. Performance considerations are also provided.

Stellar orbit evolution in close circumstellar disc encounters

The formation and early evolution of circumstellar discs often occurs within dense, newborn stellar clusters. For the first time, we apply the moving-mesh code AREPO, to circumstellar discs in 3-D, focusing on disc-disc interactions that result from stellar fly-bys. Although a small fraction of stars are expected to undergo close approaches, the outcomes of the most violent encounters might leave an imprint on the discs and host stars that will influence both their orbits and their ability to form planets. We first construct well-behaved 3-D models of self-gravitating discs, and then create a suite of numerical experiments of parabolic encounters, exploring the effects of pericenter separation r_p, disc orientation and disc-star mass ratio (M_d/M_*) on the orbital evolution of the host stars. Close encounters (2r_p<~ disc radius) can truncate discs on very short time scales. If discs are massive, close encounters facilitate enough orbital angular momentum extraction to induce stellar capture. We find that for realistic primordial disc masses M_d<~0.1M_*, non-colliding encounters induce minor orbital changes, which is consistent with analytic calculations of encounters in the linear regime. The same disc masses produce entirely different results for grazing/colliding encounters. In the latter case, rapidly cooling discs lose orbital energy by radiating away the energy excess of the shock-heated gas, thus causing capture of the host stars into a bound orbit. In rare cases, a tight binary with a circumbinary disc forms as a result of this encounter.

Simple and rapid determination of effective Murphree component efficiencies for operating absorbers, strippers and distillation columns filled with any type of trays

Estimating efficiency of an operating column has to be distinguished from that of a column being designed. This crucial point has been totally overlooked in the literature. All the methods and models available for predicting the Murphree efficiencies of tray columns have been developed for the design case. They generate their own mass and heat transfer rates and empirical parameters rather than produce true transfer rates by using operating column (realistic) data, especially the specifications of outlet streams. In addition, most of these methods are limited in application and insufficient in accuracy, especially if applied outside the range of conditions under which they were formulated.The present work introduces a general and applicable method for determining the overall Murphree component efficiencies of an operating tray column. This method uses the specifications of both inlet (feed) and outlet (product) streams of an operating column to back-calculate realistic mass and heat transfer rates for Murphree efficiency estimation. The presented method is usable to operating tray columns with any amount of flow rates and diameter as well as with any number of components and trays. Overall, it can be usable to the gas–liquid operating columns filled with any type of trays.

Synergistic cross-scale coupling of turbulence in a tokamak plasma

For the first time, nonlinear gyrokinetic simulations spanning both the ion and electron spatio-temporal scales have been performed with realistic electron mass ratio ((mD∕me)1∕2 = 60.0), realistic geometry, and all experimental inputs, demonstrating the coexistence and synergy of ion (kθρs∼O(1.0)) and electron-scale (kθρe∼O(1.0)) turbulence in the core of a tokamak plasma. All multi-scale simulations utilized the GYRO code [J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003)] to study the coupling of ion and electron-scale turbulence in the core (r/a = 0.6) of an Alcator C-Mod L-mode discharge shown previously to exhibit an under-prediction of the electron heat flux when using simulations only including ion-scale turbulence. Electron-scale turbulence is found to play a dominant role in setting the electron heat flux level and radially elongated (kr ≪ kθ) “streamers” are found to coexist with ion-scale eddies in experimental plasma conditions. Inclusion of electron-scale turbulence in these simulations is found to increase both ion and electron heat flux levels by enhancing the transport at the ion-scale while also driving electron heat flux at sub-ρi scales. The combined increases in the low and high-k driven electron heat flux may explain previously observed discrepancies between simulated and experimental electron heat fluxes and indicates a complex interaction of short and long wavelength turbulence.

On the mass estimation for FGK stars: comparison of several methods

Stellar evolutionary models simulate well binary stars when individual stellar mass and system metallicity are known. The mass can be derived directly from observations only in the case of multiple stellar systems, mainly binaries. Yet, the number of such stars for which accurate stellar masses are available is rather small. The main goal of this project is to provide realistic mass estimates for a homogeneous sample of about a thousand FGK single stars, using four different methods and techniques. We present the masses inferred according to each one of these methods as well as a final mass estimate consisting in the median of the four mass estimates. The procedures evaluated here include the use of stellar evolutionary models, mass–luminosity relation and surface gravity spectroscopic observations. By combining the results obtained with different methods, we determine the best mass value for each individual star, as well as the associated error budget. Our results confirm the expected consistency between the different mass estimation methods. None the less, for masses above 1.2 M⊙, the spectroscopic surface gravities seem to overestimate the mass. This result may be a consequence of the spectroscopic surface gravities used in this analysis. Nevertheless, this problem is minimized by the fact that we have several approaches available for deriving stellar masses. Moreover, we suggest an empirical procedure to overcome this issue.

Kirkwood gaps and diffusion along mean motion resonances in the restricted planar three-body problem

We study the dynamics of the restricted planar three-body problem near mean motion resonances, i.e. a resonance involving the Keplerian periods of the two lighter bodies revolving around the most massive one. This problem is often used to model Sun–Jupiter–asteroid systems. For the primaries (Sun and Jupiter), we pick a realistic mass ratio \mu=10^{-3} and a small eccentricity e_0&gt;0 . The main result is a construction of a variety of non local diffusing orbits which show a drastic change of the osculating (instant) eccentricity of the asteroid, while the osculating semi major axis is kept almost constant. The proof relies on the careful analysis of the circular problem, which has a hyperbolic structure, but for which diffusion is prevented by KAM tori. In the proof we verify certain non-degeneracy conditions numerically. Based on the work of Treschev, it is natural to conjecture that the time of diffusion for this problem is \sim \frac{-\ln (\mu e_0)}{\mu^{3/2} e_0} . We expect our instability mechanism to apply to realistic values of e_0 and we give heuristic arguments in its favor. If so, the applicability of Nekhoroshev theory to the three-body problem as well as the long time stability become questionable. It is well known that, in the Asteroid Belt, located between the orbits of Mars and Jupiter, the distribution of asteroids has the so-called Kirkwood gaps exactly at mean motion resonances of low order. Our mechanism gives a possible explanation of their existence. To relate the existence of Kirkwood gaps with Arnol'd diffusion, we also state a conjecture on its existence for a typical \epsilon -perturbation of the product of the pendulum and the rotator. Namely, we predict that a positive conditional measure of initial conditions concentrated in the main resonance exhibits Arnol’d diffusion on time scales \frac{- \ln \epsilon }{\epsilon^{2}} .

Influence of hadron and atmospheric models on computation of cosmic ray ionization in the atmosphere—Extension to heavy nuclei

In the last few years an essential progress in development of physical models for cosmic ray induced ionization in the atmosphere is achieved. The majority of these models are full target, i.e. based on Monte Carlo simulation of an electromagnetic-muon-nucleon cascade in the atmosphere. Basically, the contribution of proton nuclei is highlighted, i.e. the contribution of primary cosmic ray α-particles and heavy nuclei to the atmospheric ionization is neglected or scaled to protons. The development of cosmic ray induced atmospheric cascade is sensitive to the energy and mass of the primary cosmic ray particle. The largest uncertainties in Monte Carlo simulations of a cascade in the Earth atmosphere are due to assumed hadron interaction models, the so-called hadron generators. In the work presented here we compare the ionization yield functions Y for primary cosmic ray nuclei, such as α-particles, Oxygen and Iron nuclei, assuming different hadron interaction models. The computations are fulfilled with the CORSIKA 6.9 code using GHEISHA 2002, FLUKA 2011, UrQMD hadron generators for energy below 80GeV/nucleon and QGSJET II for energy above 80GeV/nucleon. The observed difference between hadron generators is widely discussed. The influence of different atmospheric parametrizations, namely US standard atmosphere, US standard atmosphere winter and summer profiles on ion production rate is studied. Assuming realistic primary cosmic ray mass composition, the ion production rate is obtained at several rigidity cut-offs – from 1GV (high latitudes) to 15GV (equatorial latitudes) using various hadron generators. The computations are compared with experimental data. A conclusion concerning the consistency of the hadron generators is stated.

Higgs boson as a top-mode pseudo-Nambu-Goldstone boson

In the spirit of the top-quark condensation, we propose a model which has a naturally light composite Higgs boson, ``tHiggs'' (${h}_{t}^{0}$), to be identified with the 126 GeV Higgs discovered at the LHC. The tHiggs, a bound state of the top quark and its flavor (vectorlike) partner, emerges as a pseudo-Nambu--Goldstone boson (NGB), ``top-mode pseudo-Nambu-Goldstone boson,'' together with the exact NGBs to be absorbed into the $W$ and $Z$ bosons as well as another (heavier) top-mode pseudo-Nambu-Goldstone bosons ($CP$-odd composite scalar, ${A}_{t}^{0}$). Those five composite (exact/pseudo-) NGBs are dynamically produced simultaneously by a single supercritical four-fermion interaction having $U(3)\ifmmode\times\else\texttimes\fi{}U(1)$ symmetry which includes the electroweak symmetry, where the vacuum is aligned by a small explicit breaking term so as to break the symmetry down to a subgroup, $U(2)\ifmmode\times\else\texttimes\fi{}U(1{)}^{\ensuremath{'}}$, in a way not to retain the electroweak symmetry, in sharp contrast to the little Higgs models. The explicit breaking term for the vacuum alignment gives rise to a mass of the tHiggs, which is protected by the symmetry and hence naturally controlled against radiative corrections. Realistic top-quark mass is easily realized similarly to the top-seesaw mechanism by introducing an extra (subcritical) four-fermion coupling which explicitly breaks the residual $U(2{)}^{\ensuremath{'}}\ifmmode\times\else\texttimes\fi{}U(1{)}^{\ensuremath{'}}$ symmetry with $U(2{)}^{\ensuremath{'}}$ being an extra symmetry besides the above $U(3{)}_{L}\ifmmode\times\else\texttimes\fi{}U(1)$. We present a phenomenological Lagrangian of the top-mode pseudo-Nambu-Goldstone bosons along with the Standard Model particles, which will be useful for the study of the collider phenomenology. The coupling property of the tHiggs is shown to be consistent with the currently available data reported from the LHC. Several phenomenological consequences and constraints from experiments are also addressed.

Right-handed neutrinos as the origin of the electroweak scale

The insular nature of the Standard Model may be explained if the Higgs mass parameter is only sensitive to quantum corrections from physical states. Starting from a scale-free electroweak sector at tree level, we postulate that quantum effects of heavy right-handed neutrinos induce a mass term for a scalar weak doublet that contains the dark matter particle. In turn, below the scale of heavy neutrinos, the dark matter sector sets the scale of the Higgs potential. We show that this framework can lead to a Higgs mass that respects physical naturalness, while also providing a viable scalar dark matter candidate, realistic light neutrino masses, and the baryon asymmetry of the Universe via thermal leptogenesis. The proposed scenario can remain perturbative and stable up to the Planck scale, thereby accommodating simple extensions to include a high-scale ($\ensuremath{\sim}2\ifmmode\times\else\texttimes\fi{}1{0}^{16}\text{ }\text{ }\mathrm{GeV}$) inflationary sector, implied by recent measurements. In that case, our model typically predicts that the dark matter scalar is close to 1 TeV in mass and could be accessible in near future direct detection experiments.

Multiple oscillatory states in models of collective neuronal dynamics.

In our previous studies, we showed that the both realistic and analytical computational models of neural dynamics can display multiple sustained states (attractors) for the same values of model parameters. Some of these states can represent normal activity while other, of oscillatory nature, may represent epileptic types of activity. We also showed that a simplified, analytical model can mimic this type of behavior and can be used instead of the realistic model for large scale simulations. The primary objective of the present work is to further explore the phenomenon of multiple stable states, co-existing in the same operational model, or phase space, in systems consisting of large number of interconnected basic units. As a second goal, we aim to specify the optimal method for state control of the system based on inducing state transitions using appropriate external stimulus. We use here interconnected model units that represent the behavior of neuronal populations as an effective dynamic system. The model unit is an analytical model (S. Kalitzin et al., Epilepsy Behav.22 (2011) S102-S109) and does not correspond directly to realistic neuronal processes (excitatory-inhibitory synaptic interactions, action potential generation). For certain parameter choices however it displays bistable dynamics imitating the behavior of realistic neural mass models. To analyze the collective behavior of the system we applied phase synchronization analysis (PSA), principal component analysis (PCA) and stability analysis using Lyapunov exponent (LE) estimation. We obtained a large variety of stable states with different dynamic characteristics, oscillatory modes and phase relations between the units. These states can be initiated by appropriate initial conditions; transitions between them can be induced stochastically by fluctuating variables (noise) or by specific inputs. We propose a method for optimal reactive control, allowing forced transitions from one state (attractor) into another.

Improvement of cloud microphysics in the aerosol-climate model BCC_AGCM2.0.1_CUACE/Aero, evaluation against observations, and updated aerosol indirect effect

A two-moment cloud microphysical scheme, to predict both the mass and number concentrations of cloud droplets and ice crystals, is implemented into the aerosol-climate model BCC_AGCM2.0.1_CUACE/Aero. The model results for aerosols, cloud properties, and meteorological fields are evaluated, and the anthropogenic aerosol indirect effect (AIE) is estimated. The new model simulates more realistic aerosol mass concentrations and optical depth compared with the original version using a one-moment bulk cloud microphysical scheme. The global annual mean column cloud droplet number concentration (CDNC) from the new model is 3.3 × 1010 m−2, which is comparable to the 4.0 × 1010 m−2 from satellite retrieval. The global annual mean cloud droplet effective radius at the cloud top from the new model is 8.1 µm, which is smaller than the 10.5 µm from observation. The simulated liquid water path (LWP) in the new model is significantly lower than that in the original model. In particular, the annual mean LWP is lower in the new model by more than 100 g m−2 in some midlatitude regions and hence much more consistent with satellite retrievals. Cloud radiative forcing and precipitation are improved to some extent in the new model. The global annual mean radiation budget at the top of the atmosphere is −0.6 W m−2, which is considerably different from the value of 1.8 W m−2 in the original model. The global annual mean anthropogenic AIE is estimated to be −1.9 W m−2 without imposing a lower bound of CDNC, whereas it is reduced significantly when a higher lower bound of CDNC is prescribed.

Dissecting the 3D structure of elliptical galaxies with gravitational lensing and stellar kinematics

AbstractThe combination of strong gravitational lensing and stellar kinematics provides a powerful and robust method to investigate the mass and dynamical structure of early-type galaxies. We demonstrate this approach by analysing two massive ellipticals from the XLENS Survey for which both high-resolution HST imaging and X-Shooter spectroscopic observations are available. We adopt a flexible axisymmetric two-component mass model for the lens galaxies, consisting of a generalised NFW dark halo and a realistic self-gravitating stellar mass distribution. For both systems, we put constraints on the dark halo inner structure and flattening, and we find that they are dominated by the luminous component within one effective radius. By comparing the tight inferences on the stellar mass from the combined lensing and dynamics analysis with the values obtained from stellar population studies, we conclude that both galaxies are characterised by a Salpeter-like stellar initial mass function.

Improving combinatorial ambiguities oftt¯events using neural networks

We present a method for resolving the combinatorial issues in the \ttbar lepton+jets events occurring at the Tevatron collider. By incorporating multiple information into an artificial neural network, we introduce a novel event reconstruction method for such events. We find that this method significantly reduces the number of combinatorial ambiguities. Compared to the classical reconstruction method, our method provides significantly higher purity with same efficiency. We illustrate the reconstructed observables for the realistic top-quark mass and the forward-backward asymmetry measurements. A Monte Carlo study shows that our method provides meaningful improvements in the top-quark measurements using same amount of data as other methods.