Production Of Dark Matter Particles Research Articles

Search for new particles in final states with a boosted top quark and missing transverse momentum in proton-proton collisions at s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s} $$\\end{document} = 13 TeV with the ATLAS detector

A search for events with one top quark and missing transverse momentum in the final state is presented. The fully hadronic decay of the top quark is explored by selecting events with a reconstructed boosted top-quark topology produced in association with large missing transverse momentum. The analysis uses 139 fb−1 of proton-proton collision data at a centre-of-mass energy of s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s} $$\\end{document} = 13 TeV recorded during 2015-2018 by the ATLAS detector at the Large Hadron Collider. The results are interpreted in the context of simplified models for Dark Matter particle production and the single production of a vector-like T quark. Without significant excess relative to the Standard Model expectations, 95% confidence-level upper limits on the corresponding cross-sections are obtained. The production of Dark Matter particles in association with a single top quark is excluded for masses of a scalar (vector) mediator up to 4.3 (2.3) TeV, assuming mχ = 1 GeV and the model couplings λq = 0.6 and λχ = 0.4 (a = 0.5 and gχ = 1). The production of a single vector-like T quark is excluded for masses below 1.8 TeV assuming a coupling to the top quark κT = 0.5 and a branching ratio for T → Zt of 25%.

Search for dark matter produced in association with a dark Higgs boson decaying into W+W− in the one-lepton final state at sqrt{s} = 13 TeV using 139 fb−1 of pp collisions recorded with the ATLAS detector

Several extensions of the Standard Model predict the production of dark matter particles at the LHC. A search for dark matter particles produced in association with a dark Higgs boson decaying into W+W− in the {ell}^{pm}nu q{overline{q}}^{prime }, final states with ℓ = e, μ is presented. This analysis uses 139 fb−1 of pp collisions recorded by the ATLAS detector at a centre-of-mass energy of 13 TeV. The W± → qoverline{q^{prime }} decays are reconstructed from pairs of calorimeter-measured jets or from track-assisted reclustered jets, a technique aimed at resolving the dense topology from a pair of boosted quarks using jets in the calorimeter and tracking information. The observed data are found to agree with Standard Model predictions. Scenarios with dark Higgs boson masses ranging between 140 and 390 GeV are excluded.

Search for the production of dark matter candidates in association with heavy dimuon resonance using the CMS open data for proton–proton collisions at sqrt{s} = 8 TeV

In this work, we present a search for the possible production of Dark Matter particles at the Large Hadron Collider alongside a new hypothetical neutral gauge boson denoted by {Z}^{prime }. The topology of the studied events is dimuons plus large missing transverse momentum. The study is performed using the CMS open data samples collected by the CMS experiment in the LHC proton–proton collisions at center-of-mass energy of 8 TeV in 2012, which corresponds to an integrated luminosity of 11.6 hbox {fb}^{-1}, and the corresponding CMS open Monte Carlo samples. Two benchmark scenarios were used for interpreting the data, the Dark Higgs scenario and the effective field theory formalism. No evidence for the existence of dark matter candidates was found. 95% confidence level limits are set on the masses of the {Z}^{prime } and the cutoff scale of the effective field theory.

Combination of searches for invisible decays of the Higgs boson using 139 fb−1 of proton-proton collision data at [formula omitted] TeV collected with the ATLAS experiment

Many extensions of the Standard Model predict the production of dark matter particles at the LHC. Sufficiently light dark matter particles may be produced in decays of the Higgs boson that would appear invisible to the detector. This Letter presents a statistical combination of searches for H→invisible decays where multiple production modes of the Standard Model Higgs boson are considered. These searches are performed with the ATLAS detector using 139 fb−1 of proton–proton collisions at a centre–of–mass energy of ▪ at the LHC. In combination with the results at ▪ and ▪, an upper limit on the H→invisible branching ratio of 0.107 (0.077) at the 95% confidence level is observed (expected). These results are also interpreted in the context of models where the 125 GeV Higgs boson acts as a portal to dark matter, and limits are set on the scattering cross-section of weakly interacting massive particles and nucleons.

The hubble rate trouble: an effective field theory of dark matter

The Hubble constant inferred from the 6-parameter fit to the CMB power spectrum conflicts with the value obtained from direct measurements via type Ia supernova and Cepheids observations. We write down effective operators involving spin-0, spin-1/2, and spin-1 dark matter that lead to the relativistic production of dark matter particles at early times, and consequently lead to an increase in the number of relativistic degrees of freedom. This mechanism which is amenable to CMB, BBN, and structure formation observables can sufficiently raise the value of the Hubble constant derived from CMB and reconcile local and CMB probes of the Hubble constant. This mechanism alone increases H_0 up to 70, textrm{km}, textrm{s}^{-1} , textrm{Mpc}^{-1}, and with the help of a Phantom-like cosmology, reach H_0 simeq 71–73 textrm{km} ,textrm{s}^{-1} textrm{Mpc}^{-1}. Lastly, we outline the region of parameter space which reproduces H_0 simeq 71–73 textrm{km} ,textrm{s}^{-1} , textrm{Mpc}^{-1} while obeying all relevant constraints.

The Hubble constant troubled by dark matter in non-standard cosmologies

The Standard Cosmological Model has experienced tremendous success at reproducing observational data by assuming a universe dominated by a cosmological constant and dark matter in a flat geometry. However, several studies, based on local measurements, indicate that the universe is expanding too fast, in disagreement with the Cosmic Microwave Background. Taking into account combined data from CMB, Baryon Acoustic Oscillation, and type Ia Supernovae, we show that if the mechanism behind the production of dark matter particles has at least a small non-thermal origin, one can induce larger values of the Hubble rate H_0, within the LambdaCDM, to alleviate the trouble with H_0. In the presence of non-standard cosmology, however, we can fully reconcile CMB and local measurements and reach H_0=70–74 {text {km s}}^{-1},{text {Mpc}}^{-1}.

Structure formation in dark matter particle production cosmology

We investigate a cosmological scenario in which the dark matter particles can be created during the evolution of the Universe. By regarding the Universe as an open thermodynamic system and using non-equilibrium thermodynamics, we examine the mechanism of gravitational particle production. In this setup, we study the large-scale structure (LSS) formation of the Universe in the Newtonian regime of perturbations and derive the equations governing the evolution of the dark matter overdensities. Then, we implement the cosmological data from Planck 2018 CMB measurements, SNe Ia and BAO observations, as well as the Riess et al. (2019) local measurement for H0 to provide some cosmological constraints for the parameters of our model. We see that the best case of our scenario (χtot2=3834.40) fits the observational data better than the baseline ΛCDM model (χtot2=3838.00) at the background level. We moreover estimate the growth factor of linear perturbations and show that the best case of our model (χfσ82=39.85) fits the LSS data significantly better than the ΛCDM model (χfσ82=45.29). Consequently, our model also makes a better performance at the level of the linear perturbations compared to the standard cosmological model. Although the improvement in χtot for Model 2 compared to ΛCDM at the background level may arise somewhat from the additional degree of freedom, the better consistency of this model at the level of linear perturbations results mainly from the impact of particle production on the sound speed at low redshifts.

Autoencoders for semivisible jet detection

The production of dark matter particles from confining dark sectors may lead to many novel experimental signatures. Depending on the details of the theory, dark quark production in proton-proton collisions could result in semivisible jets of particles: collimated sprays of dark hadrons of which only some are detectable by particle collider experiments. The experimental signature is characterised by the presence of reconstructed missing momentum collinear with the visible components of the jets. This complex topology is sensitive to detector inefficiencies and mis-reconstruction that generate artificial missing momentum. With this work, we propose a signal-agnostic strategy to reject ordinary jets and identify semivisible jets via anomaly detection techniques. A deep neural autoencoder network with jet substructure variables as input proves highly useful for analyzing anomalous jets. The study focuses on the semivisible jet signature; however, the technique can apply to any new physics model that predicts signatures with anomalous jets from non-SM particles.

Sensitivity of Future \(e^+e^-\) Colliders to Processes of Dark Matter Production with Light Mediator Exchange

One of the primary goals of the proposed future collider experiments is to search for dark matter (DM) particles using different experimental approaches. High energy $e^+e^-$ colliders offer unique possibility for the most general search based on the mono-photon signature. As any $e^+e^-$ collision process may include hard initial-state photon radiation, analysis of the energy spectrum and angular distributions of observed photons can be used to search for hard processes with an invisible final state. Dedicated procedure of merging the matrix element calculations with the lepton ISR structure function was developed to model the Standard Model background processes contributing to mono-photon signature with WHIZARD. In this work, we consider production of DM particles at the International Linear Collider (ILC) and Compact Linear Collider (CLIC) experiments via a mediator exchange. Detector effects are taken into account within the DELPHES fast simulation framework. Limits on the light DM production in a simplified model are set as a function of the mediator mass and width based on the expected two-dimensional distributions of the reconstructed mono-photon events. The experimental sensitivity is extracted in terms of the DM production cross section. Limits on the mediator couplings are then presented for a wide range of mediator masses and widths. For light mediators, for masses up to the centre-of-mass energy of the collider, coupling limits derived from the mono-photon analysis are more stringent than those expected from direct resonance searches in decay channels to SM particles.

Sensitivity of future linear hbox {e}^+hbox {e}^- colliders to processes of dark matter production with light mediator exchange

As any e^+e^- scattering process can be accompanied by a hard photon emission from the initial state radiation, the analysis of the energy spectrum and angular distributions of those photons can be used to search for hard processes with an invisible final state. Thus high energy e^+e^- colliders offer a unique possibility for the most general search of dark matter (DM) based on the mono-photon signature. We consider production of DM particles at the International Linear Collider (ILC) and Compact Linear Collider (CLIC) experiments via a light mediator exchange. Detector effects are taken into account within the Delphes fast simulation framework. Limits on the light DM production in a simplified model are set as a function of the mediator mass and width based on the expected two-dimensional distributions of the reconstructed mono-photon events. The experimental sensitivity is extracted in terms of the DM production cross section. Limits on the mediator couplings are then presented for a wide range of mediator masses and widths. For light mediators, for masses up to the centre-of-mass energy of the collider, coupling limits derived from the mono-photon analysis are more stringent than those expected from direct resonance searches in decay channels to SM particles.

Search for new phenomena in final states with b-jets and missing transverse momentum in sqrt{mathrm{s}} = 13 TeV pp collisions with the ATLAS detector

The results of a search for new phenomena in final states with b-jets and missing transverse momentum using 139 fb−1 of proton-proton data collected at a centre-of-mass energy sqrt{s} = 13 TeV by the ATLAS detector at the LHC are reported. The analysis targets final states produced by the decay of a pair-produced supersymmetric bottom squark into a bottom quark and a stable neutralino. The analysis also seeks evidence for models of pair production of dark matter particles produced through the decay of a generic scalar or pseudoscalar mediator state in association with a pair of bottom quarks, and models of pair production of scalar third-generation down-type leptoquarks. No significant excess of events over the Standard Model background expectation is observed in any of the signal regions considered by the analysis. Bottom squark masses below 1270 GeV are excluded at 95% confidence level if the neutralino is massless. In the case of nearly mass-degenerate bottom squarks and neutralinos, the use of dedicated secondary-vertex identification techniques permits the exclusion of bottom squarks with masses up to 660 GeV for mass splittings between the squark and the neutralino of 10 GeV. These limits extend substantially beyond the regions of parameter space excluded by similar ATLAS searches performed previously.

Search for Dark Matter Produced in Association with a Dark Higgs Boson Decaying into W^{±}W^{∓} or ZZ in Fully Hadronic Final States from sqrt[s]=13 TeV pp Collisions Recorded with the ATLAS Detector.

Several extensions of the Standard Model predict the production of dark matter particles at the LHC. An uncharted signature of dark matter particles produced in association with VV=W^{±}W^{∓} or ZZ pairs from a decay of a dark Higgs boson s is searched for using 139 fb^{-1} of pp collisions recorded by the ATLAS detector at a center-of-mass energy of 13TeV. The s→V(qq[over ¯])V(qq[over ¯]) decays are reconstructed with a novel technique aimed at resolving the dense topology from boosted VV pairs using jets in the calorimeter and tracking information. Dark Higgs scenarios with m_{s}>160 GeV are excluded.

Search for dark matter produced in association with a leptonically decaying {mathrm{Z}} boson in proton\u2013proton collisions at sqrt{s}=13,text {Te}text {V}

A search for dark matter particles is performed using events with a Z boson candidate and large missing transverse momentum. The analysis is based on proton–proton collision data at a center-of-mass energy of 13,text {Te}text {V}, collected by the CMS experiment at the LHC in 2016–2018, corresponding to an integrated luminosity of 137,text {fb}^{-1}. The search uses the decay channels {mathrm{Z}} rightarrow {mathrm{e}} {mathrm{e}} and {mathrm{Z}} rightarrow {{upmu }{}{}} {{upmu }{}{}} . No significant excess of events is observed over the background expected from the standard model. Limits are set on dark matter particle production in the context of simplified models with vector, axial-vector, scalar, and pseudoscalar mediators, as well as on a two-Higgs-doublet model with an additional pseudoscalar mediator. In addition, limits are provided for spin-dependent and spin-independent scattering cross sections and are compared to those from direct-detection experiments. The results are also interpreted in the context of models of invisible Higgs boson decays, unparticles, and large extra dimensions.

Origin of entropy of gravitationally produced dark matter: The entanglement entropy

We study the emergence of entropy in gravitational production of dark matter particles, ultra light scalars minimally coupled to gravity and heavier fermions, from inflation to radiation domination (RD). Initial conditions correspond to dark matter fields in their Bunch-Davies vacua during inflation. The "out" states are correlated particle-antiparticle pairs, and the distribution function is found in both cases. In the adiabatic regime the density matrix features rapid decoherence by dephasing from interference effects in the basis of "out" particle states, effectively reducing it to a diagonal form with a concomitant von Neumann entropy. We show that it is exactly the entanglement entropy obtained by tracing over one member of the correlated pairs. Remarkably, for both statistics the entanglement entropy is similar to the quantum kinetic entropy in terms of the distribution function with noteworthy differences stemming from pair correlations. The entropy and the kinetic fluid form of the energy momentum tensor all originate from decoherence of the density matrix. For ultra light scalar dark matter, the distribution function peaks at low momentum $\propto 1/k^3$ and the specific entropy is $\ll 1$. This is a hallmark of a \emph{condensed phase} but with vanishing field expectation value. For fermionic dark matter the distribution function is nearly thermal and the specific entropy is $\mathcal{O}(1)$ typical of a thermal species. We argue that the functional form of the entanglement entropy is quite general and applies to alternative production mechanisms such as parametric amplification during reheating.

Search for dark matter produced in association with a Higgs boson decaying to a pair of W bosons at CMS

The results of a search for dark matter produced in association with a Higgs boson are presented. The analysis is based on the data collected in 2016 at a center-of-mass energy of 13 TeV in proton-proton collisions with the CMS detector at the LHC, for a total integrated luminosity of 35.9 $\mathrm{fb}^{-1}$. A two-Higgs-doublet model and a baryonic Z′ model are used as benchmark. After the final selection, no significant evidence for dark matter particle production has been observed. Two-Higgs-doublet-Z′ signals with a pseudo scalar mass up to 800 GeV are excluded at 95% of CL for a Z′of mass between 1 TeV and 3 TeV. For the baryonic Z′model, Z′mediator masses up to 1.5 TeV and dark matter particle masses up to 420 GeV are excluded. The results are also reinterpreted in terms of spin-independent interaction cross-section between dark matter and nuclei, excluding values larger than $10^{-42} \mathrm{cm}^2$ for light dark matter particles.

Constraining nonthermal dark matter’s impact on the matter power spectrum

The inclusion of a period of (effective) matter domination following inflation and prior to the onset of radiation domination has interesting and observable consequences for structure growth. During this early matter-dominated era (EMDE), the Universe was dominated by massive particles, or an oscillating scalar field, that decayed into Standard Model particles, thus reheating the Universe. This decay process could also be the primary source of dark matter. In the absence of fine-tuning between the masses of the parent and daughter particles, both dark matter particles and Standard Model particles would be produced with relativistic velocities. We investigate the effects of the nonthermal production of dark matter particles with relativistic velocities on the matter power spectrum by determining the resulting velocity distribution function for the dark matter. We find that the vast majority of dark matter particles produced during the EMDE are still relativistic at reheating, so their free streaming erases the perturbations that grow during the EMDE. The free streaming of the dark matter particles can also prevent the formation of satellite galaxies around the Milky Way and the structures observed in the Lyman-$\alpha$ forest. For a given reheat temperature, these observations put an upper limit on the velocity of the dark matter particles at their creation. For example, for a reheat temperature of 10 MeV, dark matter must be produced with a Lorentz factor $\gamma \lesssim 550$.

Threshold resummation for dark-matter production at the LHC

We derive precision predictions for the production of dark-matter particles recoiling against a jet with large transverse momentum at the LHC. The dark-matter fermions are described within a simplified model and couple to the Standard Model via a vector mediator. Our predictions for the mono-jet signature include the resummation of the leading and next-to-leading threshold logarithms. The corresponding matching coefficient is evaluated at NLO. The resummed result is matched to the fixed-order NLO cross section obtained from the MadGraph framework. We discuss numerical results for several benchmark scenarios at the LHC.

Gravitational fermion creation during an anisotropic phase of cosmological expansion

The free Dirac equation is solved in a Bianchi Type I space-time, which represents a homogeneous but anisotropic universe, to show the creation of fermionic particles. It is found that unlike in the isotropic case, massless fermion production is possible. An estimate of the energy density of massless particles created during an early anisotropic phase of cosmological expansion is shown to cause substantial back-reaction on the gravitational field. The potential relevance to dark matter particle production, primordial magnetogenesis, and early universe cosmology is discussed briefly.

Melanopogenesis: dark matter of (almost) any mass and baryonic matter from the evaporation of primordial black holes weighing a ton (or less)

The evaporation of primordial black holes with a mass in the 1 gram≲ MPBH≲1000 kg range can lead to the production of dark matter particles of almost any mass in the range 0.1 MeV≲ mDM≲ 1018 GeV with the right relic density at very early times, τ≲ 10−10 s. We calculate, as a function of the primordial black holes mass and initial abundance, the combination of dark matter particle masses and number of effective dark degrees of freedom leading to the right abundance of dark matter today, whether or not evaporation stops around the Planck scale. In addition, since black hole evaporation can also lead to the production of a baryon asymmetry, we calculate where dark matter production and baryogenesis can concurrently happen, under a variety of assumptions: baryogenesis via grand unification boson decay, via leptogenesis, or via asymmetric co-genesis of dark matter and ordinary matter. Finally, we comment on possible ways to test this scenario.

Spectral Decomposition of Missing Transverse Energy at Hadron Colliders.

We propose a spectral decomposition to systematically extract information of dark matter at hadron colliders. The differential cross section of events with missing transverse energy (E_{T}) can be expressed by a linear combination of basis functions. In the case of s-channel mediator models for dark matter particle production, basis functions are identified with the differential cross sections of subprocesses of virtual mediator and visible particle production while the coefficients of basis functions correspond to dark matter invariant mass distribution in the manner of the Källén-Lehmann spectral decomposition. For a given E_{T} data set and mediator model, we show that one can differentiate a certain dark matter-mediator interaction from another through spectral decomposition.