String Network Research Articles

A Boltzmann treatment for the vorton excess problem

We derive and solve a Boltzmann equation governing the cosmological evolution of the number density of current carrying cosmic string loops, whose centrifugally supported equilibrium configurations are also referred to as vortons. The phase space is three-dimensional and consists of the time variable, the loop size, and a conserved quantum number. Our approach includes gravitational wave emission, a possibly finite lifetime for the vortons and works with any initial loop distribution and for any loop production function. We then show how our results generalize previous approaches on the vorton excess problem by tracking down the time evolution of the various sub-populations of current-carrying loops in a string network.

Differential Proteome Analysis of Chikungunya Virus Infection on Host Cells

BackgroundChikungunya virus (CHIKV) is an emerging mosquito-borne alphavirus that has caused multiple unprecedented and re-emerging outbreaks in both tropical and temperate countries. Despite ongoing research efforts, the underlying factors involved in facilitating CHIKV replication during early infection remains ill-characterized. The present study serves to identify host proteins modulated in response to early CHIKV infection using a proteomics approach.Methodology and Principal FindingsThe whole cell proteome profiles of CHIKV-infected and mock control WRL-68 cells were compared and analyzed using two-dimensional gel electrophoresis (2-DGE). Fifty-three spots were found to be differentially modulated and 50 were successfully identified by MALDI-TOF/TOF. Eight were significantly up-regulated and 42 were down-regulated. The mRNA expressions of 15 genes were also found to correlate with the corresponding protein expression. STRING network analysis identified several biological processes to be affected, including mRNA processing, translation, energy production and cellular metabolism, ubiquitin-proteasome pathway (UPP) and cell cycle regulation.Conclusion/SignificanceThis study constitutes a first attempt to investigate alteration of the host cellular proteome during early CHIKV infection. Our proteomics data showed that during early infection, CHIKV affected the expression of proteins that are involved in mRNA processing, host metabolic machinery, UPP, and cyclin-dependent kinase 1 (CDK1) regulation (in favour of virus survival, replication and transmission). While results from this study complement the proteomics results obtained from previous late host response studies, functional characterization of these proteins is warranted to reinforce our understanding of their roles during early CHIKV infection in humans.

Kinetic theory and hydrodynamics of cosmic strings

We develop further a kinetic theory of strings and derive a transport equation for a network of cosmic strings with Nambu-Goto evolution, interactions, and background gravitational effects taken into account. We prove an $H$-theorem and obtain necessary and sufficient conditions for a thermodynamic equilibrium. At the lowest order, the equilibrium is estimated by the von Mises-Fisher distributions, parametrized by mean directions and dispersions of the right- and left-moving tangent vectors. Under assumption of a local equilibrium, we derive a complete set of hydrodynamic equations that govern the evolution of strings on large scales. We also argue that on small scales, the assumption of a local equilibrium would break down, so nonequilibrium steady states, described by the Sinai-Ruelle-Bowen distributions, should be used instead.

The Neural String Network

Abstract An interactive collaborative drawing ‘machine’ designed on the concept of a neural network, allowing participants to experience a shared creative process, using the principles of open-source and social networked communication through an analogue string system. The underlying concept of the String Neural Network is to introduce participants to the idea of collaborative-shared drawing practice, as a dispersed collective that alludes to Roland Barthes The Death of the Author (1967) whereby each participant plays an equal role as both viewer and artist. Played out like a surrealist Exquisite Corpse game of consequences or as a piece of Haiku poetry, the drawing participants contribute marks, signs and signifiers to an open-content drawing, akin to the development of open-source software. The string network consists of five drawing table ‘nodes’ within a room/studio space measuring eight by eight metres square. Each node is linked to the other four via pulleys and washing lines, making it possible to peg a sheet of A4 paper to a line and winch it across to any one of the other nodes. The network system uses ten string connections between the five drawing tables, creating a pentagram within a pentagon neural network design. Representing the interconnected synapses and neurons of the brain, the role of each participant is that of cause and effect. A single instruction initiates a series of consequences that unfold in drawings, marks and patterns that are created whilst being hoisted simultaneously across the room in quick succession. The Neural String Network project was first set up in March 2012 to coincide with ‘DecodeRecode’, a telematic art project undertaken by students at MediaCityUK Salford University, as part of the centenary celebration of Alan Turing. Each participating student was given a single word drawn from the Turing theme, such as machine, brain, code and apple that were interpreted and communicated as a drawing by a collective consciousness.

Onset of rigidity in 3D stretched string networks

We extend a previously defined model consisting of connected strings with random natural lengths to three-dimensions [Delaney et al., Europhys. Lett. 72, 990 (2005)]. When this system is expanded, a threshold is reached where a fraction of the strings form a taut network. Further expansion increases the fraction of taut strings up until the point where all strings are taut and the classical problem of a spring network is recovered. We consider a number of string topologies derived from common crystal lattice structures found in nature. We analyze the properties of the system at and above the threshold expansion and demonstrate several unifying features of the model across all lattice structures considered.

PROJECTED CONSTRAINTS ON THE COSMIC (SUPER)STRING TENSION WITH FUTURE GRAVITATIONAL WAVE DETECTION EXPERIMENTS

We present projected constraints on the cosmic string tension, $G\mu/c^2$, that could be achieved by future gravitational wave detection experiments and express our results as semi-analytic relations of the form $G\mu(\Omega_{\rm gw}h^2)/c^2$, to allow for direct computation of the tension constraints for future experiments. These results can be applied to new constraints on $\ogwh$ as they are imposed. Experiments operating in different frequency bands probe different parts of the gravitational wave spectrum of a cosmic string network and are sensitive to different uncertainties in the underlying cosmic string model parameters. We compute the gravitational wave spectra of cosmic string networks based on the one-scale model, covering all the parameter space accessed by each experiment which is strongly dependent on the birth scale of loops relative to the horizon, $\alpha$. The upper limits on the string tension avoid any assumptions on the model parameters. We perform this investigation for Pulsar Timing Array experiments of different durations as well as ground-based and space-borne interferometric detectors.

Phosphoproteome dynamics reveal novel ERK1/2 MAP kinase substrates with broad spectrum of functions

The ERK1/2 MAP kinase pathway is an evolutionarily conserved signaling module that controls many fundamental physiological processes. Deregulated activity of ERK1/2 MAP kinases is associated with developmental syndromes and several human diseases. Despite the importance of this pathway, a comprehensive picture of the natural substrate repertoire and biochemical mechanisms regulated by ERK1/2 is still lacking. In this study, we used large-scale quantitative phosphoproteomics and bioinformatics analyses to identify novel candidate ERK1/2 substrates based on their phosphorylation signature and kinetic profiles in epithelial cells. We identified a total of 7936 phosphorylation sites within 1861 proteins, of which 155 classify as candidate ERK1/2 substrates, including 128 new targets. Candidate ERK1/2 substrates are involved in diverse cellular processes including transcriptional regulation, chromatin remodeling, RNA splicing, cytoskeleton dynamics, cellular junctions and cell signaling. Detailed characterization of one newly identified substrate, the transcriptional regulator JunB, revealed that ERK1/2 phosphorylate JunB on a serine adjacent to the DNA-binding domain, resulting in increased DNA-binding affinity and transcriptional activity. Our study expands the spectrum of cellular functions controlled by ERK1/2 kinases.

Fast analytic computation of cosmic string power spectra

We present analytic expressions for the cosmic string unequal time correlator (UETC) in the context of the Unconnected Segment Model. This eliminates the need to simulate the many thousands of network realizations needed to estimate the UETC numerically. With our approach we can compute the UETC very accurately, over all scales of interest, in the order of $\ensuremath{\sim}20--30$ seconds on a single CPU. Our formalism facilitates an efficient approach to computing cosmic microwave background anisotropies for cosmic strings. Discretizing the UETC and performing an eigendecomposition to act as sources in the CAMB cosmic microwave background code, the power spectrum can be calculated by summing over a finite number of eigenmodes. A much smaller number of eigenmodes are required compared to the conventional approach of averaging power spectra over a finite number of realizations of the string network. With the additional efficiency and performance improvements offered by the OpenMP CAMB code, the time required to compute string power spectra is significantly reduced compared to the standard serial CMBACT code. The latter takes $\ensuremath{\sim}30$ hours on a modern single threaded CPU for 2000 network realizations. Similar percent level accuracy can be achieved with our approach on a moderately threaded CPU (eight threads) in only $\ensuremath{\sim}15$ minutes. If accuracy is only required at the 10% level and the CPU is more highly threaded, cosmic string power spectra are now possible in $\ensuremath{\sim}2--3$ minutes. This makes exploration of the string parameter space now possible for Markov chain Monte Carlo analysis.

Weak lensing generated by vector perturbations and detectability of cosmic strings

We study the observational signature of vector metric perturbations through the effect of weak gravitational lensing. In the presence of vector perturbations, the non-vanishing signals for B-mode cosmic shear and curl-mode deflection angle, which have never appeared in the case of scalar metric perturbations, naturally arise. Solving the geodesic and geodesic deviation equations, we drive the full-sky formulas for angular power spectra of weak lensing signals, and give the explicit expressions for E-/B-mode cosmic shear and gradient-/curl-mode deflection angle. As a possible source for seeding vector perturbations, we then consider a cosmic string network, and discuss its detectability from upcoming weak lensing and CMB measurements. Based on the formulas and a simple model for cosmic string network, we calculate the angular power spectra and expected signal-to-noise ratios for the B-mode cosmic shear and curl-mode deflection angle. We find that the weak lensing signals are enhanced for a smaller intercommuting probability of the string network, P, and they are potentially detectable from the upcoming cosmic shear and CMB lensing observations. For P ∼ 10−1, the minimum detectable tension of the cosmic string will be down to Gμ ∼ 5 × 10−8. With a theoretically inferred smallest value P ∼ 10−3, we could even detect the string with Gμ ∼ 5 × 10−10.

Cosmic superstring trajectories in warped compactifications

We explore the generic motion of cosmic (super)strings when the internal compact dimensions are warped, using the Klebanov-Strassler solution as a prototypical throat geometry. We find that there is no dynamical mechanism which localises the string at the tip of the throat, but rather that the motion seems to explore both internal and external degrees of freedom democratically. This indicates that cosmic (super)strings formed by inflationary brane-antibrane annihilation will have sufficient internal motion for the gravitational wave signals from the string network to be suppressed relative to the signal from a `standard' cosmic string network.

All sky CMB map from cosmic strings integrated Sachs-Wolfe effect

By actively distorting the cosmic microwave background (CMB) over our past light cone, cosmic strings are unavoidable sources of non-Gaussianity. Developing optimal estimators able to disambiguate a string signal from the primordial type of non-Gaussianity requires calibration over synthetic full sky CMB maps, which until now had been numerically unachievable at the resolution of modern experiments. In this paper, we provide the first high resolution full sky CMB map of the temperature anisotropies induced by a network of cosmic strings since the recombination. The map has about 200 million subarcminute pixels in the healpix format which is the standard in use for CMB analyses (${N}_{\mathrm{side}}=4096$). This premiere required about 800 000 cpu-hours; it has been generated by using a massively parallel ray tracing method piercing through thousands of state of art Nambu-Goto cosmic string numerical simulations which pave the comoving volume between the observer and the last scattering surface. We explicitly show how this map corrects previous results derived in the flat sky approximation, while remaining completely compatible at the smallest scales.

Von Willebrand disease biology

*Department of Molecular Medicine and Surgery, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden; Department of Thrombosis and Hemostasis, C2-R Einthoven Laboratory for Experimental Vascular Medicine, LeidenUniversity Medical Center, Leiden, The Netherlands; Centre for Haematology, Imperial College London, HammersmithHospital Campus, London;§INSERM U770, Cedex, France; and –Department of Pathology and Molecular Medicine, QueensUniversity, Kingston, ON, Canada

BPS spectrum, indices and wall crosscxhing in $ \mathcal{N} $ = 4 supersymmetric Yang-Mills theories

BPS states in N=4 supersymmetric SU(N) gauge theories in four dimensions can be represented as planar string networks with ends lying on D3-branes. We introduce several protected indices which capture information on the spectrum and various quantum numbers of these states, give their wall crossing formula and describe how using the wall crossing formula we can compute all the indices at all points in the moduli space.

Scaling laws for weakly interacting cosmic (super)string andp-brane networks

In this paper we find new scaling laws for the evolution of $p$-brane networks in $N+1$-dimensional Friedmann-Robertson-Walker universes in the weakly-interacting limit, giving particular emphasis to the case of cosmic superstrings ($p=1$) living in a universe with three spatial dimensions (N=3). In particular, we show that, during the radiation era, the root-mean-square velocity is ${\bar v} =1/{\sqrt 2}$ and the characteristic length of non-interacting cosmic string networks scales as $L \propto a^{3/2}$ ($a$ is the scale factor), thus leading to string domination even when gravitational backreaction is taken into account. We demonstrate, however, that a small non-vanishing constant loop chopping efficiency parameter $\tilde c$ leads to a linear scaling solution with constant $L H \ll 1$ ($H$ is the Hubble parameter) and ${\bar v} \sim 1/{\sqrt 2}$ in the radiation era, which may allow for a cosmologically relevant cosmic string role even in the case of light strings. We also determine the impact that the radiation-matter transition has on the dynamics of weakly interacting cosmic superstring networks.

Stability of superconducting strings coupled to cosmic strings

We study the stability of superconducting strings in a $\mathrm{U}(1{)}_{\mathrm{local}}\ifmmode\times\else\texttimes\fi{}\mathrm{U}(1{)}_{\mathrm{global}}$ model coupled via a gauge field interaction term to U(1) Abelian-Higgs strings. The effect of the interaction on current stability is numerically investigated by varying the relevant parameters within the physical limits of our model. We find that the propagation speed of transverse (resp. longitudinal) perturbations increases (decreases) with increasing binding between the superconducting and Abelian-Higgs string. Moreover, we observe that for small enough width of the flux tube of the superconducting string and/or large enough interaction between the superconducting and the Abelian-Higgs string superconducting strings cannot carry spacelike, i.e. magnetic currents. Our model can be seen as a field theoretical realization of bound states of p F-strings and q superconducting D-strings and has important implications to vorton formation during the evolution of networks of such strings.

On exact controllability of networks of nonlinear elastic strings in 3-dimensional space

This paper concerns a system of nonlinear wave equations describing the vibrations of a 3-dimensional network of elastic strings. The authors derive the equations and appropriate nodal conditions, determine equilibrium solutions, and, by using the methods of quasilinear hyperbolic systems, prove that for tree networks the natural initial, boundary value problem has classical solutions existing in neighborhoods of the “stretched” equilibrium solutions. Then the local controllability of such networks near such equilibrium configurations in a certain specified time interval is proved. Finally, it is proved that, given two different equilibrium states satisfying certain conditions, it is possible to control the network from states in a small enough neighborhood of one equilibrium to any state in a suitable neighborhood of the second equilibrium over a sufficiently large time interval.

Physics at the planck scale: Strings and symmetries

The emergence of symmetries in the earlier proposed model of the Universe (3D network of strings in a thermal bath) is studied. The number is introduced which estimates the relative probability of changing the Gibbs distribution (or its nonequilibrium analogue) under action of stochastic forces. The principle of maximal stability (PMS) stating that only the most stable distributions are realized in the Universe is formulated. The nature of gauge symmetries and supersymmetries is discussed. According to PMS the groups SU(5) and SU(3) are advantageous. It is shown that in this model the Kaluza—Klein-Mandel-Fock unification of gravity and the Yang-Mills fields appears in the natural way. The list of thirty consequences of the model is given. They form the basis of modern physics (classical Hamiltonian mechanics, quantum mechanics, gauge symmetries, internal symmetries and so on).

Network of sodium hyaluronate with nano-knots junction of poly(amido amine) dendrimer

Amine-terminated poly(amido amine) (PAMAM) dendrimers have been attached to sodium hyaluronates (NaHAs) by a coupling reaction. The morphology of NaHAs was varied from the common network to the bead & string network, which gave rise to the decrease in viscosity of NaHAs. The bead & string network was more abundant for the covalent network complex than the noncovalent one. The beads, that is, the nano-knots of the network consist of the covalent-bonded NaHA/dendrimer composites, and the strings are NaHA chains. Beads became small and strings decreased in number with decreasing a molecular weight of NaHA. The complexation of sodium poly-l-glutamates (NaPGAs) with PAMAM dendrimers was different in the manner from that of NaHAs with dendrimers. Flexible NaPGAs produced globular composites with dendrimers.

Analytic models for the evolution of semilocal string networks

We revisit previously developed analytic models for defect evolution and adapt them appropriately for the study of semilocal string networks. We thus confirm the expectation (based on numerical simulations) that linear scaling evolution is the attractor solution for a broad range of model parameters. We discuss in detail the evolution of individual semilocal segments, focusing on the phenomenology of segment growth, and also provide a preliminary comparison with existing numerical simulations.

Predicted constraints on cosmic string tension from Planck and future CMB polarization measurements

We perform a Fisher matrix calculation of the predicted uncertainties on estimates of the cosmic string tension Gmu from upcoming observational data (namely, cosmic microwave background power spectra from the Planck satellite and an idealized future polarization experiment). We employ simulations that are more general than others commonly used in the literature, leaving the mean velocity of strings, correlation length of the string network, and "wiggliness" (which parametrizes smaller-scale structure along the strings) as free parameters that can be observationally measured. In a new code, StringFast, we implement a method for efficient computation of the C_l spectra induced by a network of strings, which is fast enough to be used in Markov Chain Monte Carlo analyses of future data. Performing a calculation with the string parameters left free results in projected constraints on Gmu that are larger than those obtained by fixing their values a priori, typically by a factor of ~2-7. We also find that if Gmu is equal to the current observational maximum, Planck will be able to make a confident detection of strings. However, if Gmu is two orders of magnitude smaller, even a perfect, lensing-free measurement of polarization power spectra will not be able to detect a nonzero string tension at better than 2 sigma confidence.