Scale Structural Problems Research Articles

Asymmetric dark matter with a spontaneously broken U(1)′ : Self-interaction and gravitational waves

Motivated by the collisionless cold dark matter small scale structure problem, we propose an asymmetric dark matter model where dark matter particle interact with each other via a massive dark gauge boson. This model easily avoid the strong limits from cosmic microwave background (CMB) observation, and have a large parameter space to be consistent with small scale structure data. We focus on a special scenario where portals between dark sector and visible sector are too weak to be detected by traditional methods. We find that this scenario can increase the effective number of neutrinos ($N_{\text{eff}}$).In addition, the spontaneous $U(1)'$ symmetry breaking process, which makes dark gauge boson massive, can generate stochastic gravitational waves with peak frequency around $10^{-6} - 10^{-7} \text{ Hz}$.

Phenomenology of a two-component dark matter model

We study a two-component dark matter model consisting of a Dirac fermion and a complex scalar charged under new U(1) gauge group in the hidden sector. The dark fermion plays the dominant component of dark matter which explains the measured DM relic density of the Universe. It has no direct coupling to ordinary standard model particles, thus evading strong constraints from the direct DM detection experiments. The dark fermion is self-interacting through the light dark gauge boson and it would be possible to address that this model can be a resolution to the small scale structure problem of the Universe. The light dark gauge boson, which interacts with the standard model sector, is also stable and composes the subdominant DM component. We investigate the model parameter space allowed by current experimental constraints and phenomenological bounds. We also discuss the sensitivity of future experiments such as SHiP, DUNE and ILC, for the obtained allowed parameter space.

Velocity-dependent self-interacting dark matter from groups and clusters of galaxies

We probe the self-interactions of dark matter with relaxed galaxy groups and clusters using observational data from strong and weak lensing and stellar kinematics. Our analysis uses the Jeans formalism and considers a wider range of systematic effects than in previous work, including adiabatic contraction and stellar anisotropy, to robustly constrain the self-interaction cross section. For both groups and clusters, our results show a mild preference for a nonzero cross section compared with cold collisionless dark matter. Our groups result, σ/m=0.5±0.2 cm2/g, places the first constraint on self-interacting dark matter (SIDM) at an intermediate scale M200∼ 1014 M⊙ between galaxies and massive clusters. For massive clusters with M200∼ 1015 M⊙, our result is σ/m=0.19±0.09 cm2/g, with an upper limit of σ / m < 0.35 cm2/g (95% CL) . Thus, our results disfavor a velocity-independent cross section of order 1 cm2/g or larger needed to impact small scale structure problems in galaxies, but are consistent with a velocity-dependent cross section that decreases with increasing scattering velocity. Comparing the cross sections with and without the effect of adiabatic contraction, we find that adiabatic contraction produces slightly larger values for our data sample, but they are consistent at the 1σ level. Finally, to validate our approach, we apply our Jeans analysis to a sample of mock data generated from SIDM-plus-baryons simulations with σ/m = 1 cm2/g. This is the first test of the Jeans model at the level of stellar and lensing observables directly measured from simulations. We find our analysis gives a robust determination of the cross section, as well as consistently inferring the true baryon and dark matter density profiles.

Freeze-in dark matter from secret neutrino interactions

We investigate a simplified freeze-in dark-matter model in which the dark matter only interacts with the standard-model neutrinos via a light scalar. The extremely small coupling for the freeze-in mechanism is naturally realized in several neutrino-portal scenarios with the secret neutrino interactions. We study possible evolution history of the hidden sector: the dark sector would undergo pure freeze-in production if the interactions between the dark-sector particles are negligible, while thermal equilibrium within the dark sector could occur if the reannihilation of the dark matter and the scalar mediator is rapid enough. We investigate the relic abundance in the freeze-in and dark freeze-out regimes, calculate evolution of the dark temperature, and study its phenomenological aspects on BBN and CMB constraints, the indirect-detection signature, as well as the potential to solve the small scale structure problem.

The Limits of Dignity at the Intersection of Autonomy, Identity and Affect: A Cautionary Tale from the Supreme Court of Canada

This survey of the Supreme Court of Canada’s pivotal anti-discrimination rulings over a 30-year period assesses the extent to which the shifting nature of the grounds approach and the Court’s conceptions of dignity together form part of a gendered system of enunciation at the intersection of autonomy, identity and affect. This article is written as a corrective to some of the author’s early optimism about the possibilities that dignity may offer in the context of constitutional equality rights cases and as a cautionary tale for those who would attempt to use it as a vehicle for rights claiming through the courts. These cases reveal that in the context of Canadian anti-discrimination law, the concept of dignity is most often used to circumscribe agency, limit subjectivity and curtail possibilities for redress by reducing large scale structural problems to the individual in ways that reproduce law’s originary violence.

Bound Dark Matter (BDM) towards solving the small scale structure problem

Cosmological observations such as structure formation, cosmic microwave background, and cosmic distance ladder set tight constraints to the amount and nature of dark matter (DM) . In particular structure formation strongly constraints not only the amount of energy density but also the time when DM became non-relativistic, anr. Standard cold and thermic warm DM particles have a smooth transition from being relativistic at high energies to a non-relativistic regime since the mass of these particles is constant while the velocity redshifts with the expansion of the universe. However, here we explore the possibility that the DM particle acquires a non-perturbative mass at a phase transition scale and a scale factor ac, e.g. the mass of protons and neutrons is due to the binding energy of QCD through a non-perturbative process. This transition acquired a more fundamental meaning for the Bound Dark Matter (BDM) model because they describe a particle getting its mass through a non-perturbative process. These BDM particles may go from being relativistic to non-relativistic at ac, which implies an abrupt transition of the velocity of the particles vc at that time, affecting the equation of state and the cosmological evolution. Here we study the cosmological impact of the values of vc and the scale transition ac and they by reducing the free-streaming scale and therefore the small scale structure. Using CMB Plank, Supernovae SNIa, and baryon acoustic oscillation data, we constrain the valid region in the parameter space ac − vc putting upper bounds to ac but not restricting vc. For instance, the transition must be ac < 2.66 × 10−6 for 0vc = . We also find that the free-streaming and the Jeans mass of the dark matter particle is highly influenced by the velocity vc, for example, a 3 keV WDM have a Jeans mass of Mfs = 1.97 × 107 M⊙/h3 but an equivalent BDM with the same anr but an abrupt transition in the velocity, vc ∼ 0 would have a Jeans mass of Mfs = 2.08×104 M⊙/h3 which significantly changes the large scale structure formation.

Boosted self-interacting dark matter in a multi-component dark matter model

In models of multi-component dark matter, the lighter component of dark matter can be boosted by annihilations of the heavier state if mass splitting is large enough. Such relativistic dark matter can be detectable via large neutrino detectors such as Super-Kamiokande and IceCube. Moreover, if the process is inelastic scattering and decay length of the produced particle is short enough, another signature coming from the decay can also be detectable. In this paper, we construct a simple two-component dark matter model with a hidden U(1)D gauge symmetry where the lighter component of dark matter has a potential to improve the so-called small scale structure problems with large self-interacting cross section. We estimate number of multi-Cherenkov ring events due to both of the boosted dark matter and subsequent decay of the particle produced by inelastic scattering at Hyper-Kamiokande future experiment. Some relevant constraints, such as dark matter direct detection and cosmological observations, are also taken into account. The numerical analysis shows that some parameter space which can induce large self-interacting cross section can give a few multi-Cherenkov ring events per year at Hyper-Kamiokande.

A new structural reanalysis approach based on the polynomial-type extrapolation methods

In this study, a new approach based on the polynomial-type extrapolation methods is applied to the approximate structural reanalysis under multiple and large changes in the initial design. In this approach, the sequences of approximate displacement of the modified structure are constructed by using a fixed-point iteration method. These sequences are then further analyzed by two polynomial-type vector extrapolation methods to find the approximate response of the modified structure more accurately, namely, the minimal polynomial extrapolation (MPE) and the reduced rank extrapolation (RRE). Based on a single initial design, the MPE and RRE methods approximate the displacement vector of the modified structure by solving a least-squares problem which is much smaller than the original system of equations of the exact analysis. The accuracy and efficiency of this reanalysis approach is evaluated on three large scale structural reanalysis problems under multiple and large changes in their initial designs. The obtained reanalysis results demonstrate that the MPE and RRE methods not only yield accurate results, but also are computationally efficient.

Self-interacting inelastic dark matter: a viable solution to the small scale structure problems

Self-interacting dark matter has been proposed as a solution to the small-scale structure problems, such as the observed flat cores in dwarf and low surface brightness galaxies. If scattering takes place through light mediators, the scattering cross section relevant to solve these problems may fall into the non-perturbative regime leading to a non-trivial velocity dependence, which allows compatibility with limits stemming from cluster-size objects. However, these models are strongly constrained by different observations, in particular from the requirements that the decay of the light mediator is sufficiently rapid (before Big Bang Nucleosynthesis) and from direct detection. A natural solution to reconcile both requirements are inelastic endothermic interactions, such that scatterings in direct detection experiments are suppressed or even kinematically forbidden if the mass splitting between the two-states is sufficiently large. Using an exact solution when numerically solving the Schrödinger equation, we study such scenarios and find regions in the parameter space of dark matter and mediator masses, and the mass splitting of the states, where the small scale structure problems can be solved, the dark matter has the correct relic abundance and direct detection limits can be evaded.

Formula omitted] WIMP and SIMP Dark Matter from a Global U(1) Breaking

We propose and study a scalar extension of the Standard Model which respects a Z3 symmetry remnant of the spontaneous breaking of a global U(1)DM symmetry. The model has a dark matter candidate whose relic density is determined by three classes of processes: the usual self-annihilation, semi-annihilation and purely dark matter 3→2 processes. The latter has been subject of recent interest leading to the so-called 'Strongly Interacting Massive Particle' (SIMP) scenario. We show under which conditions the model can lead to a concrete realization of such scenario and study the possibility that the dark matter self-interactions could address the small scale structure problems. In particular, we find that in order for the SIMP scenario to work, the dark matter mass must be in the range of 100 MeV, with the global symmetry energy breaking scale in the TeV range.

3.5 keV X-ray line signal from dark matter decay in local U(1)B−L extension of Zee-Babu model

We consider a local $U(1)_{B-L}$ extension of Zee-Babu model to explain the recently observed 3.5 keV X-ray line signal. The model has three Standard model (SM)-singlet Dirac fermions with different $U(1)_{B-L}$ charges. A complex scalar field charged under $U(1)_{B-L}$ is introduced to break the $U(1)_{B-L}$ symmetry. After $U(1)_{B-L}$ symmetry breaking a remnant discrete symmetry stabilizes the lightest state of the Dirac fermions, which can be a stable dark matter (DM). The second lightest state, if mass splitting with the stable DM is about 3.5 keV, decays dominantly to the stable DM and 3.5 keV photon through two-loop diagrams, explaining the X-ray line signal. Two-loop suppression of the decay amplitude makes its lifetime much longer than the age of the universe and it can be a decaying DM candidate in large parameter region. We also introduce a real scalar field which is singlet under both the SM and $U(1)_{B-L}$ and can explain the current relic abundance of the Dirac fermionic DMs. If the mixing with the SM Higgs boson is small, it does not contribute to DM direct detection. The main contribution to the scattering of DM off atomic nuclei comes from the exchange of $U(1)_{B-L}$ gauge boson, $Z'$, and is suppressed below current experimental bound when $Z'$ mass is heavy ($\gtrsim 10$ TeV). If the singlet scalar mass is about 0.1-10 MeV, the DM self-interaction can be large enough to solve small scale structure problems in simulations with the cold DM, such as, the core-vs-cusp problem and too-big-to-fail problem.

WIMP and SIMP dark matter from the spontaneous breaking of a global group

We propose and study a scalar extension of the Standard Model which respects a ℤ3 symmetry remnant of the spontaneous breaking of a global U(1)DM symmetry. Consequently, this model has a natural dark matter candidate and a Goldstone boson in the physical spectrum. In addition, the Higgs boson properties are changed with respect to the Standard Model due to the mixing with a new particle. We explore regions in the parameter space taking into account bounds from the measured Higgs properties, dark matter direct detection as well as measurements of the effective number of neutrino species before recombination. The dark matter relic density is determined by three classes of processes: the usual self-annihilation, semi-annihilation and purely dark matter 3 → 2 processes. The latter has been subject of recent interest leading to the so-called `Strongly Interacting Massive Particle' (SIMP) scenario. We show under which conditions our model can lead to a concrete realization of such scenario and study the possibility that the dark matter self-interactions could address the small scale structure problems. In particular, we find that in order for the SIMP scenario to work, the dark matter mass must be in the range 7−115 MeV, with the global symmetry energy breaking scale in the TeV range.

Constraints and consequences of reducing small scale structure via large dark matter-neutrino interactions

Cold dark matter explains a wide range of data on cosmological scales. However, there has been a steady accumulation of evidence for discrepancies between simulations and observations at scales smaller than galaxy clusters. One promising way to affect structure formation on small scales is a relatively strong coupling of dark matter to neutrinos. We construct an experimentally viable, simple, renormalizable model with new interactions between neutrinos and dark matter and provide the first discussion of how these new dark matter-neutrino interactions affect neutrino phenomenology. We show that addressing the small scale structure problems requires asymmetric dark matter with a mass that is tens of MeV. Generating a sufficiently large dark matter-neutrino coupling requires a new heavy neutrino with a mass around 100 MeV. The heavy neutrino is mostly sterile but has a substantial τ neutrino component, while the three nearly massless neutrinos are partly sterile. This model can be tested by future astrophysical, particle physics, and neutrino oscillation data. Promising signatures of this model include alterations to the neutrino energy spectrum and flavor content observed from a future nearby supernova, anomalous matter effects in neutrino oscillations, and a component of the τ neutrino with mass around 100 MeV.

A new multi-swarm multi-objective optimization method for structural design

In this paper, a new multi-objective optimization method is proposed to solve large scale structural problems in continuous search space. This method is based on the recently developed algorithm, so called charged system search (CSS), which has been used for single objective optimization. In this study the aim is to develop a multi-objective optimization algorithm with higher convergence rate compared to the other well-known methods to enable to deal with multi-modal optimization problems having many design variables. In this method, the CSS algorithm is utilized as a search engine in combination with clustering and particle regeneration procedures. The proposed method is examined for four mathematical functions and two structural problems, and the results are compared to those of some other state-of-art approaches.

High Performance Hybrid Direct-Iterative Solution Method for Large Scale Structural Analysis Problems

High performance direct-iterative hybrid linear solver for large scale finite element problem is developed. Direct solution method is robust but difficult to parallelize, whereas iterative solution method is opposite for direct method. Therefore, combining two solution methods is desired to get both high performance parallel efficiency and numerical robustness for large scale structural analysis problems. Hybrid method mentioned in this paper is based on FETI-DP (Finite Element Tearing and Interconnecting-Dual Primal method) which has good parallel scalability and efficiency. It is suitable for fourth and second order finite element elliptic problems including structural analysis problems. We are using the hybrid concept of theses two solution method categories, combining the multifrontal solver into FETI-DP based iterative solver. Hybrid solver is implemented for our general structural analysis code, IPSAP.

Simultaneous Solution to Dark Matter and Flavor Problems of Supersymmetry

Neutralino dark matter is well motivated, but also suffers from two shortcomings: it requires gravity-mediated supersymmetry breaking, which generically violates flavor constraints, and its thermal relic density Omega is typically too large. We propose a simple solution to both problems: neutralinos freeze-out with Omega approximately 10-100, but then decay to approximately 1 GeV gravitinos, which are simultaneously light enough to satisfy flavor constraints and heavy enough to be all of dark matter. This scenario is naturally realized in high-scale gauge-mediation models, ameliorates small scale structure problems, and implies that "cosmologically excluded" models may, in fact, be cosmologically preferred.

Superweakly Interacting Massive Particle Solutions to Small Scale Structure Problems

Collisionless, cold dark matter in the form of weakly interacting massive particles (WIMPs) is well motivated in particle physics, naturally yields the observed relic density, and successfully explains structure formation on large scales. On small scales, however, it predicts too much power, leading to cuspy halos, dense cores, and large numbers of subhalos, in apparent conflict with observations. We consider super-WIMP dark matter, produced with large velocity in late decays at times 10(5) - 10(8) s. As analyzed by Kaplinghat in a more general setting, we find that super-WIMPs have sufficiently large free-streaming lengths and low phase space densities to help resolve small scale structure problems while preserving all of the above-mentioned WIMP virtues.

Modeling of containment structures on high performance computers

With recent advances in parallel supercomputers and network-connected workstations, the solution of large scale structural engineering problems, such as containment structures, has now become tractable. High-performance computer architectures, which are usually available at large universities and national laboratories, now can solve large nonlinear problems. At the other end of the spectrum, network connected workstations can be configured to become a distributed-parallel computer. A description of the development of a parallelized finite element computer program for the solution of static nonlinear structural mechanics problems is presented here. Also, a finite element methodology is presented for use in finding the structural capacity of reinforced concrete structures. The method is applicable to both cylindrical and rectilinear geometries. Containment structures for nuclear reactors are the final barrier between released radionuclides and the public. Containment structures are constructed from steel, reinforced concrete, or prestressed concrete. US nuclear reactor containment geometries tend to be cylindrical with elliptical or hemispherical heads. The older Soviet designed reactors do not use a containment building to mitigate the effects of accidents. Instead, they employed a sealed set of rectilinear, interconnected compartments, collectively called the accident localization system (ALS), to reduce the release of radionuclides to the atmosphere during accidents. As an illustrative example, the methodology developed herein is applied to a generic VVER-440/V213 design subjected to internal overpressure.

Massive neutrinos, neutrino oscillations and neutrino hot dark matter in a standard model extension

We present a simple extension of the standard model of electroweak interactions that accommodates existing and recent data on neutrinos. The model contains a scalar triplet carrying two units of lepton number and a vector-like neutral lepton in addition to the usual bosons and fermions of the standard model. The model also accounts for the hot dark matter component required in mixed dark matter models that attempt to solve the large scale structure problem.

Multiple scale finite element methods

AbstractNew temporal and spatial discretization methods are developed for multiple scale structural dynamic problems. The concept of fast and slow time scales is introduced for the temporal discretization. The required time step is shown to be dependent only on the slow time scale, and therefore, large time steps can be used for high frequency problems. To satisfy the spatial counterpart of the requirement on time step constraint, finite‐spectral elements and finite wave elements are developed. Finite‐spectral element methods combine the usual finite elements with the fast convergent spectral functions to obtain a faster convergence rate; whereas, finite wave elements are developed in parallel to the temporal shifting technique. Therefore, the spatial resolution is increased substantially. These methods are especially applicable to structural acoustics and linear space structures. Numerical examples are presented to illustrate the effectiveness of these methods.