Strong Self-interaction Research Articles

Gravitational collapse of Bose-Einstein condensate dark matter halos with logarithmic nonlinearity

"If dark matter is composed of massive bosons, a Bose-Einstein Condensation process must have occurred during the cosmological evolution. Therefore galactic dark matter may be in a form of a condensate, characterized by a strong self-interaction. One of the interesting forms of the self-interaction potential of the condensate dark matter is the logarithmic form. In the present work we investigate one of the astrophysical implications of the condensate dark matter with logarithmic self-interaction, namely, its gravitational collapse. To describe the condensate dark matter we use the Gross-Pitaevskii equation, and the Thomas-Fermi approximation. By using the hydrodynamic representation of the Gross-Pitaevskii equation we obtain the equation of state of the condensate, which has the form of the ideal gas equation of state, with the pressure proportional to the dark matter density. In the Thomas-Fermi approximation, the evolution equations of the condensate reduce to the classical continuity, and Euler equations of fluid dynamics. We obtain the equations of motion of the condensate radius in spherical symmetry, by assuming certain particular forms for the velocity and density of the condensate. The collapse time required for the formation of a stable macroscopic astrophysical object is obtained in an integral form, and explicit numerical estimations for the formation of astrophysical objects with masses ranging from 106M⊙ to 1012M⊙ are presented."

Accurate Electronic Properties and Intercalation Voltages of Olivine-Type Li-Ion Cathode Materials from Extended Hubbard Functionals

The design of novel cathode materials for Li-ion batteries would greatly benefit from accurate first-principles predictions of structural, electronic, and magnetic properties as well as intercalation voltages in compounds containing transition-metal elements. For such systems, density-functional theory (DFT) with standard (semi-)local exchange-correlation functionals is of limited use as it often fails due to strong self-interaction errors that are especially relevant in the partially filled $d$ shells. Here, we perform a detailed comparative study of the phospho-olivine cathode materials Li$_x$MnPO$_4$, Li$_x$FePO$_4$, and the mixed transition metal Li$_x$Mn$_{1/2}$Fe$_{1/2}$PO$_4$ ($x=0, 1/4, 1/2, 3/4, 1$) using four electronic-structure methods: DFT, DFT+$U$, DFT+$U$+$V$, and HSE06. We show that DFT+$U$+$V$, with onsite $U$ and intersite $V$ Hubbard parameters determined from first principles and self-consistently with respect to the structural parameters by means of density-functional perturbation theory (linear response), provides the most accurate description of the electronic structure of these challenging compounds. In particular, we demonstrate that DFT+$U$+$V$ displays very clearly "digital" changes in oxidation states of the transition-metal ions in all compounds, including the mixed-valence phases occurring at intermediate Li concentrations, leading to voltages in remarkable agreement with experiments. We show that the inclusion of intersite Hubbard interactions is essential for the accurate prediction of thermodynamic quantities, balancing the drive for localization induced by the onsite $U$ with intersite $V$ orbital hybridizations.

Consequences of neutron decay inside neutron stars

The hypothesis that neutrons might decay into dark matter is explored using neutron stars as a testing ground. It is found that in order to obtain stars with masses at the upper end of those observed, the dark matter must experience a relatively strong self-interaction. Conservation of baryon number and energy then require that the star must undergo some heating, with a decrease in radius, leading to an increase in speed of rotation over a period of days.

The impact of dark matter on neutron stars with antikaon condensations

In this paper, we study the impact of dark matter (DM) on neutron stars (NSs) that contain antikaon (including [Formula: see text] and [Formula: see text]) condensations. DM is assumed to be made of nonself annihilating, but strongly or weakly self-interacting fermions. The competition between DM and antikaon condensations makes the gross stellar properties and neutrino emission features of NSs change violently. Results show that the role of antikaon condensations on DM-admixed NSs with weak self-interaction among DM particles is considerable. However, the effect of antikaon condensations with strong self-interaction seems feeble. DM with weak self-interaction favors the occurrence of antikaon condensations in turn, and both [Formula: see text] and [Formula: see text] condensations are allowed in low-mass DM-admixed NSs. With the fixed medium stellar mass, the neutrino emissivity at the core of the DM-admixed NS with antikaon condensations becomes much lower than that in normal NS matter.

Holography of time machines

We use holography to examine the response of interacting quantum fields to the appearance of closed timelike curves in a dynamically evolving background that initially does not contain them. For this purpose, we study a family of two-dimensional spacetimes that model very broad classes of wormhole time machines. The behavior of strongly coupled conformal theories in these spacetimes is then holographically described by three-dimensional AdS bulk geometries that we explicitly construct. The dual bulk spacetime is free from any divergences, but splits into two disconnected components, without and with CTCs, which are joined only through the boundary; then, passages across the chronology horizon are impossible for any field excitations. In dual terms, the strong self-interaction of the CFT decouples the pathological part from the rest of the spacetime. We also find that entangling the CFTs in two separate time machines connects them through a traversable bulk wormhole. Nevertheless, any entanglement-assisted chronology violations will be prevented by quantum bulk corrections, i.e., subleading 1/N effects, again without needing any gravitational backreaction of the CFT. We are led to speculate that chronology may be protected without involving Planck scale physics.

Cosmological structure formation in scalar field dark matter with repulsive self-interaction: the incredible shrinking Jeans mass

ABSTRACT Scalar field dark matter (SFDM) comprised of ultralight (≳ 10−22 eV) bosons is an alternative to standard, collisionless cold dark matter (CDM) that is CDM-like on large scales but inhibits small-scale structure formation. As a Bose–Einstein condensate, its free-field (‘fuzzy’) limit (FDM) suppresses structure below the de Broglie wavelength, λdeB, creating virialized haloes with central cores of radius ∼ λdeB, surrounded by CDM-like envelopes, and a halo mass function (HMF) with a sharp cut-off on small scales. With a strong enough repulsive self-interaction (SI), structure is inhibited, instead, below the Thomas–Fermi (TF) radius, RTF (the size of an SI-pressure-supported (n = 1)-polytrope), when RTF > λdeB. Previously, we developed tools to describe SFDM dynamics on scales above λdeB and showed that SFDM-TF haloes formed by Jeans-unstable collapse from non-cosmological initial conditions have RTF-sized cores, surrounded by CDM-like envelopes. Revisiting SFDM-TF in the cosmological context, we simulate halo formation by cosmological infall and collapse, and derive its transfer function from linear perturbation theory to produce cosmological initial conditions and predict statistical measures of structure formation, such as the HMF. Since FDM and SFDM-TF transfer functions both have small-scale cut-offs, we can align them to let observational constraints on FDM proxy for SFDM-TF, finding FDM with particle masses 1 ≲ m/(10−22 eV/c2) ≲ 30 corresponds to SFDM-TF with 10 ≳ RTF/(1 pc) ≳ 1, favouring subgalactic (sub-kpc) core size. The SFDM-TF HMF cuts off gradually, however, leaving more small-mass haloes: Its Jeans mass shrinks so fast that scales filtered early can still recover and grow!

Core-envelope haloes in scalar field dark matter with repulsive self-interaction: fluid dynamics beyond the de Broglie wavelength

ABSTRACT Scalar field dark matter (SFDM) comprised of ultralight bosons has attracted great interest as an alternative to standard, collisionless cold dark matter (CDM) because of its novel structure-formation dynamics, described by the coupled Schrödinger–Poisson equations. In the free-field (‘fuzzy’) limit of SFDM (FDM), structure is inhibited below the de Broglie wavelength, but resembles CDM on larger scales. Virialized haloes have ‘solitonic’ cores of radius ∼λdeB, surrounded by CDM-like envelopes. When a strong enough repulsive self-interaction (SI) is also present, structure can be inhibited below a second length-scale, λSI, with λSI > λdeB – called the Thomas–Fermi (TF) regime. FDM dynamics differ from CDM because of quantum pressure, and SFDM-TF differs further by adding SI pressure. In the small-λdeB limit, however, we can model all three by fluid conservation equations for a compressible, γ = 5/3 ideal gas, with ideal gas pressure sourced by internal velocity dispersion and, for the TF regime, an added SI pressure, PSI ∝ ρ2. We use these fluid equations to simulate halo formation from gravitational collapse in 1D, spherical symmetry, demonstrating for the first time that SFDM-TF haloes form with cores the size of RTF, the radius of an SI-pressure-supported (n = 1)-polytrope, surrounded by CDM-like envelopes. In comparison with rotation curves of dwarf galaxies in the local Universe, SFDM-TF haloes pass the [‘too-big-to-fail’ + ‘cusp–core’]-test if RTF ≳ 1 kpc.

Strong dark matter self-interaction from a stable scalar mediator

In face of the small-scale structure problems of the collisionless cold dark matter (DM) paradigm, a popular remedy is to introduce a strong DM self-interaction which can be generated nonperturbatively by a MeV-scale light mediator. However, if such a mediator is unstable and decays into SM particles, the model is severely constrained by the DM direct and indirect detection experiments. In the present paper, we study a model of a self-interacting fermionic DM, endowed with a light stable scalar mediator. In this model, the DM relic abundance is dominated by the fermionic DM particle which is generated mainly via the freeze-out of its annihilations to the stable mediator. Since this channel is invisible, the DM indirect detection constraints should be greatly relaxed. Furthermore, the direct detection signals are suppressed to an unobservable level since fermionic DM scatterings with a nucleon appear at one-loop level. By further studying the bounds from the CMB, supernovae and BBN on the visible channels involving the dark sector, we show that there is a large parameter space which can generate appropriate DM self-interactions at dwarf galaxy scales, while remaining compatible with other experimental constraints.

Kinetic Ising models with self-interaction: Sequential and parallel updating.

Kinetic Ising models on the square lattice with both nearest-neighbor interactions and self-interaction are studied for the cases of random sequential updating and parallel updating. The equilibrium phase diagrams and critical dynamics are studied using Monte Carlo simulations and analytic approximations. The Hamiltonians appearing in the Gibbs distribution describing the equilibrium properties differ for sequential and parallel updating but in both cases feature multispin and non-nearest-neighbor couplings. For parallel updating the system is a probabilistic cellular automaton and the equilibrium distribution satisfies detailed balance with respect to the dynamics [E. N. M. Cirillo, P. Y. Louis, W. M. Ruszel and C. Spitoni, Chaos Solitons Fractals 64, 36 (2014)CSFOEH0960-077910.1016/j.chaos.2013.12.001]. In the limit of weak self-interaction for parallel dynamics, odd and even sublattices are nearly decoupled and checkerboard patterns are present in the critical and low temperature regimes, leading to singular behavior in the shape of the critical line. For sequential updating the equilibrium Gibbs distribution satisfies global balance but not detailed balance and the Hamiltonian is obtained perturbatively in the limit of weak nearest-neighbor dynamical interactions. In the limit of strong self-interaction the equilibrium properties for both parallel and sequential updating are described by a nearest-neighbor Hamiltonian with twice the interaction strength of the dynamical model.

Self-interacting dark matter with a vector mediator: kinetic mixing with the mathrm{U}{(1)}_{{left(B-Lright)}_3} gauge boson

A spontaneously broken hidden U(1)h gauge symmetry can explain both the dark matter stability and the observed relic abundance. In this framework, the light gauge boson can mediate the strong dark matter self-interaction, which addresses astrophysical observations that are hard to explain in collisionless cold dark matter. Motivated by flavoured grand unified theories, we introduce right-handed neutrinos and a flavoured B − L gauge symmetry for the third family mathrm{U}{(1)}_{{left(B-Lright)}_3} . The unwanted relic of the U(1)h gauge boson decays into neutrinos via the kinetic mixing with the mathrm{U}{(1)}_{{left(B-Lright)}_3} gauge boson. Indirect detection bounds on dark matter are systematically weakened, since dark matter annihilation results in neutrinos. However, the kinetic mixing between mathrm{U}{(1)}_{{left(B-Lright)}_3} and U(1)Y gauge bosons are induced by quantum corrections and leads to an observable signal in direct and indirect detection experiments of dark matter. This model can also explain the baryon asymmetry of the Universe via the thermal leptogenesis. In addition, we discuss the possibility of explaining the lepton flavour universality violation in semi-leptonic B meson decays that is recently found in the LHCb experiment.

Slowly rotating Bose Einstein condensate galactic dark matter halos, and their rotation curves

If dark matter is composed of massive bosons, a Bose–Einstein condensation process must have occurred during the cosmological evolution. Therefore galactic dark matter may be in a form of a condensate, characterized by a strong self-interaction. We consider the effects of rotation on the Bose–Einstein condensate dark matter halos, and we investigate how rotation might influence their astrophysical properties. In order to describe the condensate we use the Gross–Pitaevskii equation, and the Thomas–Fermi approximation, which predicts a polytropic equation of state with polytropic index n=1. By assuming a rigid body rotation for the halo, with the use of the hydrodynamic representation of the Gross–Pitaevskii equation we obtain the basic equation describing the density distribution of the rotating condensate. We obtain the general solutions for the condensed dark matter density, and we derive the general representations for the mass distribution, boundary (radius), potential energy, velocity dispersion, tangential velocity and for the logarithmic density and velocity slopes, respectively. Explicit expressions for the radius, mass, and tangential velocity are obtained in the first order of approximation, under the assumption of slow rotation. In order to compare our results with the observations we fit the theoretical expressions of the tangential velocity of massive test particles moving in rotating Bose–Einstein condensate dark halos with the data of 12 dwarf galaxies and the Milky Way, respectively.

Nanostructure of propylammonium nitrate in the presence of poly(ethylene oxide) and halide salts.

Nanoscale structure of protic ionic liquids is critical to their utility as molecular electrochemical solvents since it determines the capacity to dissolve salts and polymers such as poly(ethylene oxide) (PEO). Here we use quantum chemical molecular dynamics simulations to investigate the impact of dissolved halide anions on the nanostructure of an archetypal nanostructured protic ionic liquid, propylammonium nitrate (PAN), and how this impacts the solvation of a model PEO polymer. At the molecular level, PAN is nanostructured, consisting of charged/polar and uncharged/nonpolar domains. The charged domain consists of the cation/anion charge groups, and is formed by their electrostatic interaction. This domain solvophobically excludes the propyl chains on the cation, which form a distinct, self-assembled nonpolar domain within the liquid. Our simulations demonstrate that the addition of Cl- and Br- anions to PAN disrupts the structure within the PAN charged domain due to competition between nitrate and halide anions for the ammonium charge centre. This disruption increases with halide concentration (up to 10 mol. %). However, at these concentrations, halide addition has little effect on the structure of the PAN nonpolar domain. Addition of PEO to pure PAN also disrupts the structure within the charged domain of the liquid due to hydrogen bonding between the charge groups and the terminal PEO hydroxyl groups. There is little other association between the PEO structure and the surrounding ionic liquid solvent, with strong PEO self-interaction yielding a compact, coiled polymer morphology. Halide addition results in greater association between the ionic liquid charge centres and the ethylene oxide components of the PEO structure, resulting in reduced conformational flexibility, compared to that observed in pure PAN. Similarly, PEO self-interactions increase in the presence of Cl- and Br- anions, compared to PAN, indicating that the addition of halide salts to PAN decreases its utility as a molecular solvent for polymers such as PEO.

Blow-Up Phenomena for Gradient Flows of Discrete Homogeneous Functionals

We investigate gradient flows of some homogeneous functionals in R^N , arising in the Lagrangian approximation of systems of self-interacting and diffusing particles. We focus on the case of negative homogeneity. In the case of strong self-interaction, the functional possesses a cone of negative energy. It is immediate to see that solutions with negative energy at some time become singular in finite time, meaning that a subset of particles concentrate at a single point. Here, we establish that all solutions become singular in finite time for the class of functionals under consideration. The paper is completed with numerical simulations illustrating the striking non linear dynamics when initial data have positive energy.

Stable equilibrium point and oscillatory motion of the Universe in a model with variable vacuum energy

We discuss the mechanism by which the field vacuum energy varies as a result of strong self-interaction. We propose a non-perturbative approach to treat strong interactions and discuss the problem in terms of quasi-particles describing the motion of field modes. The resulting vacuum energy is variable and depends on the state of the system. If the interacting scalar field is related to the cosmological field, an acceleration equation with a stable equilibrium point follows in a simple model, predicting the oscillatory behavior of the scale factor and other cosmological effects.

Hyperbolic deformation of a gauge field theory and the hierarchy problem

The problem of the gauge hierarchy is brought up in a hypercomplex scheme for a [Formula: see text] field theory; in such a scheme, a compact gauge group is deformed through a [Formula: see text]-parameter that varies along a noncompact internal direction, transverse to the [Formula: see text] compact one, and thus an additional [Formula: see text] gauge symmetry is incorporated. This transverse direction can be understood as an extra internal dimension, which will control the spontaneous symmetry breakdown, and will allow us to establish a mass hierarchy. In this mechanism, there is no brane separation to be estabilized as in the braneworld paradigm, however, a different kind of fine-tuning is needed in order to generate the wished electroweak/Planck hierarchy. By analyzing the effective self-interactions and mass terms of the theory, an interesting duality is revealed between the real and hybrid parts of the effective potential. This duality relates the weak and strong self-interaction regimes of the theory, due to the fact that both mass terms and self-coupling constants appear as one-parameter flows in [Formula: see text]. Additionally, the [Formula: see text]-deformation will establish a flow for the electromagnetic coupling that mimics the renormalization group flow for the charge in QED.

Entrapment of Water at the Transmembrane Helix-Helix Interface of Quiescin Sulfhydryl Oxidase 2.

Little is known about how a membrane can regulate interactions between transmembrane helices. Here, we show that strong self-interaction of the transmembrane helix of human quiescin sulfhydryl oxidase 2 rests on a motif of conserved amino acids comprising one face of the helix. Atomistic molecular dynamics simulations suggest that water molecules enter the helix-helix interface and connect serine residues of both partner helices. In addition, an interfacial tyrosine can interact with noninterfacial water or lipid. Dimerization of this transmembrane helix might therefore be controlled by membrane properties controlling water permeation and/or by the lipid composition of the membrane.

Predicting the Role of a Single Amino Acids in the Dimerization of Transmembrane Helices

Single-span membrane proteins take part in biological processes. In many cases their function has been shown to require dimerization via their transmembrane domains (TMDs). Research into the dimerization of TMDs has revealed sequence dependence, driven by a combination of amino acids. The helix interactions of multi-pass membrane proteins are well understood, as analysis of crystal structures shows that helix interfaces tend to contain small, polar and highly conserved residues. Unfortunately, for single-pass proteins structural data is scarce.The aim of this study is to characterize interfaces of TMDs that show strong self-interaction. In one study of this kind, we examine amino acid composition and conservation in order to identify patterns characteristic of interface residues. Our aim is to develop a method to predict the TMD interfaces from sequences alone.We used the ToxR assay in Escherichia coli to measure TMD homodimerization. In this assay, dimerization driven by TMDs results in the transcriptional activation of ctx promoter, inducing the expression of a reporter enzyme. The amount of reporter enzyme activity is a measure of the strength of the dimerization.Here, we present the scanning mutagenesis followed by ToxR analysis of 10 TMDs with strong self-interaction. Mutations were made to all amino acids within the TM helix. Some TMD interfaces were found to contain sequence patterns previously associated with parallel helix interactions, such as the GxxxG motif. However, in other cases motif searching would not have identified the interface, and the key residues in the interactions were diverse. The conservation of each amino acid in each TMD was calculated based on amino acid alignments against homologs. Preliminary analysis shows that amino acid conservation is a good indicator for the interface of some, but not all interacting TMDs.

Directional detection of dark matter in universal bound states

It has been suggested that several small-scale structure anomalies in $\Lambda$CDM cosmology can be solved by strong self-interaction between dark matter particles. It was shown by Braaten and Hammer that the presence of a near threshold S-wave resonance can make the scattering cross section at nonrelativistic speeds come close to saturating the unitarity bound. This can result in the formation of a stable bound state of two asymmetric dark matter particles (we call the bound state as darkonium). Laha and Braaten studied the nuclear recoil energy spectrum in dark matter direct detection experiments due to this incident bound state. Here we study the angular recoil spectrum, and show that it is uniquely determined up to normalization by the S-wave scattering length. Observing this angular recoil spectrum in a dark matter directional detection experiment will uniquely determine many of the low-energy properties of dark matter independent of the underlying dark matter microphysics.

Galactic center excess in γ rays from annihilation of self-interacting dark matter.

Observations by the Fermi Large-Area Telescope have uncovered a significant γ-ray excess directed toward the MilkyWay Galactic Center. There has been no detection of a similar signal in the stacked population of MilkyWay dwarf spheroidal galaxies. Additionally, astronomical observations indicate that dwarf galaxies and other faint galaxies are less dense than predicted by the simplest cold dark matter models. We show that a self-interacting dark matter model with a particle mass of roughly 50GeV annihilating to the mediator responsible for the strong self-interaction can simultaneously explain all three observations. The mediator is necessarily unstable, and its mass must be below about 100MeV in order to decrease the dark matter density of faint galaxies. If the mediator decays to electron-positron pairs with a cross section on the order of the thermal relic value, then we find that these pairs can up-scatter the interstellar radiation field in the Galactic center and produce the observed γ-ray excess.

Optical Origin of Subnanometer Resolution in Tip-Enhanced Raman Mapping

Raman spectroscopy and imaging at the single-molecular level in both signal sensitivity and spatial resolution have been a long dream. A recent experimental study of single-molecule Raman mapping with a subnanometer resolution by using a tip-enhanced Raman scattering (TERS) technique is a great step closer to this great dream. However, how the subnanometer spatial resolution is possible with a Raman excitation light spot (“hot spot”) of diameter over 10 nm formed between the tip–substrate nanogap to excite and probe the molecule still remains mysterious. Here we present an optical theory of Raman scattering that accounts for the strong near-field self-interaction of molecule with the plasmonic nanogap due to multiple elastic scattering of light by the molecule. The result shows that the self-interaction effect strongly modulates the Raman excitation and radiation in both the signal intensity and spatial sensitivity, leading to a “super-hot spot” and subnanometer lateral resolution of Raman mapping. The optical theory can help to uncover the full picture of light-matter interaction of atoms and molecules with plasmonic nanostructures and explore unknown frontiers of physics and chemistry at nanoscale.