Spin-dependent Case Research Articles

XQC and CSR constraints on strongly interacting dark matter with spin and velocity dependent cross sections

Dark matter that interacts strongly with baryons can avoid the stringent dark matter direct detection constraints, because, like baryons, they are likely to be absorbed when traversing the rocks, leading to a suppressed flux in deep underground labs. Such strongly interacting dark matter, however, can be probed by dark matter experiments or other experiments operated on the ground level or in the atmosphere. In this paper we carry out systematic analysis of two of these experiments, XQC and CSR, to compute the experimental constraints on the strongly interacting dark matter in the following three scenarios: (1) spin-independent and spin-dependent interactions; (2) different velocity dependent cross sections; (3) different dark matter mass fractions. Some of the scenarios are first analyzed in the literature. We find that the XQC exclusion region has some non-trivial dependencies on the various parameters and the limits in the spin-dependent case is quite different from the spin-independent case. A peculiar region in the parameter space, where the XQC constraint disappears, is also found in our Monte Carlo simulations. This occurs in the case where the interaction cross section is proportional to the square of the velocity. We further compare our XQC and CSR limits to other experimental constraints, and find that a large parameter space is allowed by various experiments if the dark matter mass fraction is sufficiently small, fχ ≲ 10-4.

Spin-dependent scattering of boosted dark matter

Boosted dark matter is a promising method for probing light dark matter, with a well-developed computational framework for spin-independent scattering already existing. The spin-dependent case, on the other hand, lacks a coherent treatment. We therefore give the first comprehensive derivation of the spin-dependent scattering cross section for boosted dark matter, finding that certain effects can lead to enhanced experimental sensitivity compared to the conventional contact interaction. For example, when the transfer momentum is sufficiently large, the time component of the dark matter current contributes significantly to the proton structure factor. Also, even without a light mediator, we find a residual momentum dependence in the quark-nucleon matching operation that can contribute similarly. We promote this endeavor by deriving direct limits on sub-GeV spin-dependent scattering of boosted dark matter from terrestrial data. We find that the exclusion limits from the boosted structure factor differ by as much as six orders of magnitude from those calculated using nonrelativistic structure factors.

Constraints on dark matter scattering with long lived mediators from observations of the Sun with the Fermi Large Area Telescope

The Sun represents a promising target for indirect dark matter searches, as dark matter particles from the Galactic halo can be gravitationally trapped in its core or in external orbits, and their annihilations can lead to final states with standard model particles that are able to reach the Earth. In this work we have considered a scenario in which dark matter particles can annihilate into pairs of long-lived mediators, which in turn can escape from the Sun and decay into pairs of gamma rays or into the bb̅, τ + τ -, μ + μ - channels, with the production of gamma rays in the final states. All these processes are expected to yield an excess in the energy spectrum of gamma rays towards the Sun. We have therefore analyzed the data collected by the Fermi Large Area Telescope during its first 13.5 years of operation, searching for possible excesses in the solar gamma-ray spectrum. Since no statistically significant excess is found, we have set constraints on the dark matter-nucleon scattering cross sections in both the spin-dependent and spin-independent cases. For all the mediator decay channels explored and for dark matter masses between a few GeV/c2 and 1 TeV/c2, we have found that the upper limits on the spin-dependent and spin-independent cross sections are in the ranges from 10-45 to 10-39 cm2 and from 10-47 up to 10-42 cm2, respectively.

COSINE-100 and DAMA/LIBRA-phase2 in WIMP effective models

Assuming a standard Maxwellian for the WIMP velocity distribution, we obtain the bounds from null WIMP search results of 59.5 days of COSINE-100 data on the DAMA/LIBRA-phase2 modulation effect within the context of the non-relativistic effective theory of WIMP-nucleus scattering. Here, we systematically assume that one of the effective operators allowed by Galilean invariance dominates in the effective Hamiltonian of a spin-1/2 dark matter (DM) particle. We find that, although DAMA/LIBRA and COSINE-100 use the same sodium-iodide target, the comparison of the two results still depends on the particle-physics model. This is mainly due to two reasons: i) the WIMP signal spectral shape; ii) the expected modulation fractions, when the upper bound on the time-averaged rate in COSINE-100 is converted into a constraint on the annual modulation component in DAMA/LIBRA . We find that the latter effect is the dominant one. For several effective operators the expected modulation fractions are larger than in the standard spin-independent or spin-dependent interaction cases. As a consequence, compatibility between the modulation effect observed in DAMA/LIBRA and the null result from COSINE-100 is still possible for several non-relativistic operators. At low WIMP masses such relatively high values of the modulation fractions arise because COSINE-100 is mainly sensitive to WIMP-sodium scattering events, due to the higher threshold compared to DAMA/LIBRA . A next COSINE analysis is expected to have a full sensitivity for the 5 σ region of DAMA/LIBRA.

Spin-dependent electron transport through a Mn-phthalocyanine molecule — A steady-state density functional theory (SS-DFT) study

We generalize the recently proposed steady-state density functional theory (SS-DFT) to spin-dependent cases and theoretically investigate the electronic and transport properties of a Mn-phthalocyanine molecule sandwiched between two graphene nanoribbon leads. The junction filters spin-up (minority spin) electrons while allowing spin-down (majority spin) electrons to pass with a filtering efficiency of about 99.5% at low biases. The spin-down electrons are found to tunnel through the junction via the HOMO orbital of the Mn-phthalocyanine molecule. Detailed analysis of the spin-dependent electron tunneling mechanism as well as the electronic/magnetic properties of the junction is presented.

Pinning down inelastic dark matter in the Sun and in direct detection

We study the solar capture rate of inelastic dark matter with endothermic and/or exothermic interactions. By assuming that an inelastic dark matter signal will be observed in next generation direct detection experiments we can set a lower bound on the capture rate that is independent of the local dark matter density, the velocity distribution, the galactic escape velocity as well as the scattering cross section. In combination with upper limits from neutrino observatories we can place upper bounds on the annihilation channels leading to neutrinos. We find that, while endothermic scattering limits are weak in the isospin-conserving case, strong bounds may be set for exothermic interactions, in particular in the spin-dependent case. Furthermore, we study the implications of observing two direct detection signals, in which case one can halo-independently obtain the dark matter mass and the mass splitting, and disentangle the endothermic/exothermic nature of the scattering. Finally we discuss isospin violation.

MOSCAB: direct dark matter search using the geyser technique

The MOSCAB experiment (Materia OSCura A Bolle) uses the Geyser technique for dark matter search. The results of the first 0.5 kg mass prototype detector using superheated C3F8 liquid were very encouraging, achieving a 5 keV nuclear recoil threshold with high insensitivity to gamma radiation. Additionally, the technique seems to be easily scalable to higher masses for both in terms of complexity and costs, resulting in a very competitive technique for direct dark matter search, especially for the spin dependent case. Here, we report as well in the construction and commissioning of the big detector of 40 kg at the Milano-Bicocca University. The detector, the calibration tests and the evaluation of the background will be presented. Once demonstrated the functionality of the detector, it will be operated at the Gran Sasso National Laboratory in 2015.

The two-photon exchange contribution to muonic hydrogen from chiral perturbation theory

We compute the spin-dependent and spin-independent structure functions of the forward virtual-photon Compton tensor of the proton at O(p3) using heavy baryon effective theory including the Delta particle. We compare with previous results when existing. Using these results we obtain the leading hadronic contributions, associated to the pion and Delta particles, to the Wilson coefficients of the lepton–proton four fermion operators in NRQED. The spin-independent coefficient yields a pure prediction for the two-photon exchange contribution to the muonic hydrogen Lamb shift, ΔETPE(π&Δ)=34(13) μeV. We also compute the charge, 〈rn〉, and Zemach, 〈rn〉(2), moments for n≥3. Finally, we discuss the spin-dependent case, for which we compute the difference between the four-fermion Wilson coefficients relevant for hydrogen and muonic hydrogen.

Unitary group approach to the many-electron correlation problem: spin-dependent operators

Following a brief overview of the unitary group approach (UGA) to the many-electron correlation problem, focusing in particular on Shavitt’s contribution via his graphical unitary group approach, we present a short review of our earlier results for the evaluation of matrix elements (MEs) of unitary group generators or products of generators in the electronic Gel’fand–Tsetlin basis with the help of spin-adapted second-quantization-like creation and annihilation vector operators at the unitary group level. This formalism is then extended to a spin-dependent case that is required when accounting for relativistic effects by developing explicit expressions for MEs of spin-orbital creation and annihilation operators in terms of the standard spin-adapted UGA basis. This leads naturally to a segmentation of these MEs and enables the evaluation of spin-dependent one-body operators while relying largely on the segment values of the standard spin-independent UGA.

Earthly probes of the smallest dark matter halos

Dark matter kinetic decoupling involves elastic scattering of dark matter off of leptons and quarks in the early universe, the same process relevant for direct detection and for the capture rate of dark matter in celestial bodies; the resulting size of the smallest dark matter collapsed structures should thus correlate with quantities connected with direct detection rates and with the flux of high-energy neutrinos from dark matter annihilation in the Sun or in the Earth. In this paper we address this general question in the context of two widely studied and paradigmatic weakly-interacting particle dark matter models: the lightest neutralino of the minimal supersymmetric extension of the Standard Model, and the lightest Kaluza-Klein particle of Universal Extra Dimensions (UED). We argue and show that while the scalar neutralino-nucleon cross section correlates poorly with the kinetic decoupling temperature, the spin-dependent cross section exhibits a strong correlation in a wide range of models. In UED models the correlation is present for both cross sections, and is extraordinarily tight for the spin-dependent case. A strong correlation is also found, for both models, for the flux of neutrinos from the Sun, especially for fluxes large enough to be at potentially detectable levels. We provide analytic guidance and formulae that illustrate our findings.

Review on Non-directional Direct Dark Matter Searches

An overview of non-directional direct detection methods is given. The currently leading experiments for spin independent WIMPs interactions are using simultaneous measurement of two quantities for event-by-event background discrimination in cryogenic bolometers and noble gas like xenon. Besides these, several interesting techniques have been developped, each having a specific advantage concerning e.g energy threshold lowering or strong immunity to ionizing radiations background. Technologies used and most recent results about spin-dependent and spin-independent cases are presented.

Designing Dirac points in two-dimensional lattices

We present a framework to elucidate the existence of accidental contacts of energy bands, particularly those called Dirac points which are the point contacts with linear energy dispersions in their vicinity. A generalized von-Neumann-Wigner theorem we propose here gives the number of constraints on the lattice necessary to have contacts without fine tuning of lattice parameters. By counting this number, one could quest for the candidate of Dirac systems without solving the secular equation. The constraints can be provided by any kinds of symmetry present in the system. The theory also enables the analytical determination of k-point having accidental contact by selectively picking up only the degenerate solution of the secular equation. By using these frameworks, we demonstrate that the Dirac points are feasible in various two-dimensional lattices, e.g. the anisotropic Kagome lattice under inversion symmetry is found to have contacts over the whole lattice parameter space. Spin-dependent cases, such as the spin-density-wave state in LaOFeAs with reflection symmetry, are also dealt with in the present scheme.

LOCV CALCULATIONS FOR POLARIZED LIQUID 3He WITH THE SPIN-DEPENDENT CORRELATION

We have used the lowest order constrained variational (LOCV) method to calculate some ground-state properties of polarized liquid 3 He at zero temperature with the spin-dependent correlation function employing the Lennard–Jones and Aziz pair potentials. We have seen that the total energy of polarized liquid 3 He increases with increasing polarization. For all polarizations, it is shown that the total energy in the spin-dependent case is lower than the spin-independent case. We have seen that the difference between the energies of spin-dependent and spin-independent cases decreases by increasing the polarization. We have shown that the main contribution of the potential energy comes from the spin-triplet state.

Symmetric group approach to spin-dependent CI

A general algorithm of configuration interaction (CI) method for spin-dependent Hamiltonians in a basis of spin-adapted N-electron configuration state functions is formulated. The method is derived from the symmetric group approach (SGA) to a many-electron problem and retains the simple structure of the spin-independent CI. The transition from an algorithm for a spin-independent Hamiltonian to a general spin-dependent case results in a replacement of the blocks of irreducible representation matrices of the symmetric group (representing permutation operators in the spin-adapted N-electron basis) by larger matrices representing the pertinent spin operators. The structure of the algorithm, in particular the set of loops in the orbital graph leading to non-zero contributions to the CI matrix elements, remains exactly the same as in the spin-independent case.

Isolated photons at hadron colliders at O( ααS2) (II): Spin-dependent case

The cross section for inclusive prompt photon production with polarized hadron beams is calculated at order αα s 2 using the phase-space slicing or analytic/Monte Carlo method. Isolation cuts are placed on the photon and the results are compared to a previous fully analytic calculation. Numerical results for the isolated cross section are presented for pp → γ + X at RHIC centre-of-mass energies with plausible isolation parameters using the most modern polarized parton densities evolved in next-to-leading order QCD. The perturbative stability of the asymmetries and scale dependence of the results are briefly discussed.

A dynamical model for nuclear structure functions

We construct a dynamical model for the parton distributions in a nucleus by perturbative evolution of input distributions from a low starting scale. These input distributions are obtained by modifications of the corresponding free nucleon ones; the modifications being determined by standard nuclear physics considerations. The model gives good agreement with existing data. Its extension to the spin dependent case enables an estimation of nuclear modifications to asymmetries observed in recent doubly polarised deep inelastic scattering experiments. Although the structure functions themselves are very different from the free nucleon ones, their ratio is insensitive to these changes.

2-jet production in polarised $$\vec p\vec p$$ collisions

Following recent interest in the subject of polarisation phenomena, we discuss the cross-sections and polarisation asymmetry in 2-jet production in polarised proton-polarised proton (\(\vec p\vec p\)) scattering. We set up a complete set of parametrisations for the proton spin-dependent parton densities and use them to demonstrate that this cross-section is dominated by gluonic terms. Hence, a measurement of the asymmetry in such processes will provide information on the gluon spin-dependent density. We further show that a factorisation of the hadronic cross-section a la Combridge and Maxwell's work in unpolarised 2-jet production also applies to the spin-dependent case. Hence, the cross-section can be written in terms of a genericpolarised parton density, which can then be measured in the process.

A FORTRAN program for numerical solution of the Altarelli-Parisi equations by the Laguerre method

We review the Laguerre method for solving the Altarelli-Parisi equations. The Laguerre method allows one to expand quark/parton distributions and splitting functions in orthonormal polynomials. The desired quark distributions are themselves expanded in terms of evolution operators, and we derive the integrodifferential equations satisfied by the evolution operators. We give relevant equations for both flavor nonsinglet and singlet distributions, for both spin-independent and spin-dependent distributions. We discuss stability and accuracy of the results using this method. For intermediate values of Bjorken x(0.03< x<0.7), one can obtain accurate results with a modest number of Laguerre polynomials ( N≈20); we discuss requirements for convergence also for the regions of large or small x. A FORTRAN program is provided which implements the Laguerre method; test results are given for both the spin-independent and spin-dependent cases.

QCD evolution of the spin structure functions of the neutron and proton.

Models of the long-distance behavior of QCD can be used to make predictions for the twist-two piece of the current correlation function appearing in deep-inelastic scattering. The connection between the model predictions, valid at a four-momentum transfer squared {ital Q}{sup 2} of the order of 1 (GeV/{ital c}){sup 2}, and the data, collected at much higher {ital Q}{sup 2}, is provided by perturbative QCD. We present here the details of a method, previously used for spin-averaged lepton scattering, applied to the spin-dependent case. We then use the method to make predictions for the spin structure functions {ital g}{sub 1}{sup proton} and {ital g}{sub 1}{sup neutron}.

A generalisation of the Luttinger model

A generalised Luttinger model is proposed and studied in the spinless and spin-dependent cases. The solution of the back-scattering and Umklapp scattering problems are obtained using a new strategy. For the standard Luttinger model the results already known are obtained again.