Constraints on Mediator-based Dark Matter and Scalar Dark Energy Models Using [square Roots]s PDF Download

Author: Anne Kathrin Becker
Publisher:
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Category :
Languages : en
Pages :

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Abstract: Constraints on selected mediator-based dark matter models and a scalar dark energy model using up to 37 fb−1s√ = 13 TeV pp collision data collected by the ATLAS detector at the LHC during 2015-2016 are summarised in this paper. The results of experimental searches in a variety of final states are interpreted in terms of a set of spin-1 and spin-0 single-mediator dark matter simplified models and a second set of models involving an extended Higgs sector plus an additional vector or pseudo-scalar mediator. The searches considered in this paper constrain spin-1 leptophobic and leptophilic mediators, spin-0 colour-neutral and colour-charged mediators and vector or pseudo-scalar mediators embedded in extended Higgs sector models. In this case, also s√ = 8 TeV pp collision data are used for the interpretation of the results. The results are also interpreted for the first time in terms of light scalar particles that could contribute to the accelerating expansion of the universe (dark energy)

Author: [Study Group] ATLAS Collaboration CERN
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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Abstract: Results from a wide range of searches targeting different experimental signatures with and without missing transverse momentum (EmissT) are used to constrain a Two-Higgs-Doublet Model (2HDM) with an additional pseudo-scalar mediating the interaction between ordinary and dark matter (2HDM+a). The analyses use up to 139 fb−1 of proton-proton collision data at a centre-of-mass energy s√=13 TeV recorded with the ATLAS detector at the Large Hadron Collider between 2015-2018. The results from three of the most sensitive searches are combined statistically. These searches target signatures with large EmissT and a leptonically decaying Z boson; large EmissT and a Higgs boson decaying to bottom quarks; and production of charged Higgs bosons in final states with top and bottom quarks, respectively. Constraints are derived for several common as well as new benchmark scenarios within the 2HDM+a

Author: Sabino Matarrese
Publisher: Springer Science & Business Media
ISBN: 9048186854
Category : Science
Languages : en
Pages : 413

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This book brings together reviews from leading international authorities on the developments in the study of dark matter and dark energy, as seen from both their cosmological and particle physics side. Studying the physical and astrophysical properties of the dark components of our Universe is a crucial step towards the ultimate goal of unveiling their nature. The work developed from a doctoral school sponsored by the Italian Society of General Relativity and Gravitation. The book starts with a concise introduction to the standard cosmological model, as well as with a presentation of the theory of linear perturbations around a homogeneous and isotropic background. It covers the particle physics and cosmological aspects of dark matter and (dynamical) dark energy, including a discussion of how modified theories of gravity could provide a possible candidate for dark energy. A detailed presentation is also given of the possible ways of testing the theory in terms of cosmic microwave background, galaxy redshift surveys and weak gravitational lensing observations. Included is a chapter reviewing extensively the direct and indirect methods of detection of the hypothetical dark matter particles. Also included is a self-contained introduction to the techniques and most important results of numerical (e.g. N-body) simulations in cosmology. " This volume will be useful to researchers, PhD and graduate students in Astrophysics, Cosmology Physics and Mathematics, who are interested in cosmology, dark matter and dark energy.

Author: Data Mania
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Category :
Languages : en
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Recent observations in cosmology suggest that the universe is undergoing accelerating expansion. Mysterious component responsible for acceleration is called "Dark Energy" contributing to 70% of total energy density of the universe. Simplest DE model is [Lambda]CDM, where Einsteins cosmological constant plays role of the dark energy. Despite the fact that it is consistent with observational data, it leaves some important theoretical questions unanswered. To overcome these difficulties different Dark energy models are proposed. Two of these models XCDM parametrization and slow rolling scalar field model [phi]CDM, along with "standard" [Lambda]CDM are disscussed here, constraining their parameter set. In this thesis we start with a general theoretical overview of basic ideas and distance measures in cosmology. In the following chapters we use H II starburst galaxy apparent magnitude versus redshift data from Siegel et al.(2005) to constrain DE model parameters. These constraints are generally consistent with those derived using other data sets, but are not as restrictive as the tightest currently available constraints. Also we constrain above mentioned cosmological models in light of 32 age measurements of passively evolving galaxies as a function of redshift and recent estimates of the product of the cosmic microwave background acoustic scale and the baryon acoustic oscillation peak scale.

Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 52

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Dark matter interacting via the exchange of a light pseudoscalar can induce observable signals in indirect detection experiments and experience large self-interactions while evading the strong bounds from direct dark matter searches. The pseudoscalar mediator will however induce flavour-changing interactions in the Standard Model, providing a promising alternative way to test these models. We investigate in detail the constraints arising from rare meson decays and fixed target experiments for different coupling structures between the pseudoscalar and Standard Model fermions. The resulting bounds are highly complementary to the information inferred from the dark matter relic density and the constraints from primordial nucleosynthesis. We discuss the implications of our findings for the dark matter self-interaction cross section and the prospects of probing dark matter coupled to a light pseudoscalar with direct or indirect detection experiments. In particular, we find that a pseudoscalar mediator can only explain the Galactic Centre excess if its mass is above that of the B mesons, and that it is impossible to obtain a sufficiently large direct detection cross section to account for the DAMA modulation.

Author: Paul Moder
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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Abstract: The Standard Model (SM) is the only model in particle physics containing all observed elementary particles and their interactions. Over the years, its predictions were tested and observed in a number of experiments. However, there are still observations that can not be explained by the SM with one of the most prominent ones being the existence of Dark Matter (DM). While the existence of DM was first theorised through astronomical observations, extensions of the SM allow for a search of DM at the Large Hadron Collider (LHC) as well. Since DM can not be detected directly, final states analysing its existence at the LHC are always designed around high missing transverse energy. This thesis presents a search for DM with data collected by the ATLAS detector in the years 2015-2018 corresponding to an integrated luminosity of 139~\mathrm{fb}^{-1}$ at a center of mass energy of 13~\TeV. The analysis is based on an extended two Higgs doublet model (2HDM+a) where a pseudo-scalar mediator allows the production of DM in the final state. In addition to the DM, a top quark and a \Wboson-boson are produced in the final state. This thesis mainly focuses on a final state with zero leptons which results in both the \Wboson-boson and the top quark being required to decay hadronically. In addition to that, the \Wboson-boson can be expected to have a high momentum in the signal process. Therefore, a dedicated identification algorithm using large-radius jets is employed to select events with at least one hadronically decaying \Wboson-boson. This allows for a strong distinction against SM background events. In this analysis, several different signal processes are considered, since different parameters can affect the cross section and the distributions of the signal processes. These parameters include different values for the mass of the mediator $a$, the mass of the heavy Higgs boson $H$ and $\tan\beta$. Since no significant excess was found in the signal regions when comparing SM prediction to data, upper exclusion limits on the cross section of the signal processes were calculated with a 95\% confidence level (CL). These limits are presented in three different model parameter planes. One such plane presents the upper limits for different values of the mass of the mediator, $m_a$, and the mass of the heavy Higgs boson, $m_H$, while keeping $\tan\beta = 1$. The second and third plane present the upper limits for different values of the mass of the heavy Higgs boson, $m_H$, and $\tan\beta$ while the mass of the mediator $a$ stays constant at $m_a = 250~\GeV$ and $m_a = 150~\GeV$. In addition to the upper limits for signal processes with one top quark in the final state, this thesis also provides an upper exclusion limit where this signal process is combined with a process that includes two top quarks in the final state

Author: Agnieszka M. Cieplak
Publisher:
ISBN: 9781303211751
Category :
Languages : en
Pages : 99

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This thesis addresses astrophysical probes to constrain dark matter (DM) and dark energy models. Primordial black holes (PBHs) remain one of the few DM candidates within the Standard Model of Particle Physics. This thesis presents a new probe of this PBH DM, using the microlensing of the source stars monitored by the already existing Kepler satellite. With its photometric precision and the large projected cross section of the nearby stars, it is found that previous constraints on PBH DM could theoretically be extended by two orders of magnitude. Correcting a well-known microlensing formula, a limb-darkening analysis is included, and a new approximation is calculated for future star selection. A preliminary prediction is calculated for the planned Wide-Field Infrared Survey Telescope. A preliminary study of the first two years of publicly available Kepler data is presented. The investigation yields many new sources of background error not predicted in the theoretical calculations, such as stellar flares and comets in the field of view. Since no PBH candidates are detected, an efficiency of detection is therefore calculated by running a Monte Carlo with fake limb-darkened finite-source microlensing events. It is found that with just the first 8 quarters of data, a full order of magnitude of the PBH mass range can be already constrained. Finally, one of the astrophysical probes of dark energy is also addressed - specifically, the baryon acoustic oscillations (BAO) measurement in the gas distribution, as detected in quasar absorption lines. This unique measurement of dark energy at intermediate redshifts is being measured by current telescope surveys. The last part of this thesis therefore focuses on understanding the systematic effects in such a detection. Since the bias between the underlying dark matter distribution and the measured gas flux distribution is based on gas physics, hydrodynamic simulations are used to understand the evolution of neutral hydrogen over time. It is found the location of the peak is a dependable measurement, but more robust simulations will have to be run for a full understanding of the shape and size of the peak.

Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 118

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We study the interplay of flavor and dark matter phenomenology for models of flavored dark matter interacting with quarks. We allow an arbitrary flavor structure in the coupling of dark matter with quarks. This coupling is assumed to be the only new source of violation of the Standard Model flavor symmetry extended by a U(3)x associated with the dark matter. We call this ansatz Dark Minimal Flavor Violation (DMFV) and highlight its various implications, including an unbroken discrete symmetry that can stabilize the dark matter. As an illustration we study a Dirac fermionic dark matter [chi] which transforms as triplet under U(3)x, and is a singlet under the Standard Model. The dark matter couples to right-handed down-type quarks via a colored scalar mediator [Phi] with a coupling [lambda]. We identify a number of "flavor-safe" scenarios for the structure of [lambda] which are beyond Minimal Flavor Violation. For dark matter and collider phenomenology we focus on the well-motivated case of b-flavored dark matter. The combined flavor and dark matter constraints on the parameter space of [lambda] turn out to be interesting intersections of the individual ones. LHC constraints on simplified models of squarks and sbottoms can be adapted to our case, and monojet searches can be relevant if the spectrum is compressed.

Author: Grace Dupuis
Publisher:
ISBN:
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Languages : en
Pages :

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"The identity and nature of dark matter (DM) is one of the most important open questions in physics. The idea that dark matter is some exotic particle species is a leading hypothesis, and is strongly supported by cosmological data that favours non-baryonic particle dark matter. Although the Standard Model (SM) of particle physics has been extremely successful in describing observed phenomena, the absence of a DM candidate, in addition to many other unresolved questions, motivates the search for new physics. This thesis presents a study constraining new physics beyond the SM with experimental results, primarily from the Large Hadron Collider (LHC), in several models that are motivated by providing candidates for particle dark matter. The following models and their associated collider signatures are investigated. A Z′ model, in which the extra U(1)′ gauge group is kinetically mixed with the SM hypercharge is first considered. The experimental limits from dilepton production are used to constrain the Z′ mass and kinetic mixing parameter. Contributions of the invisible Z′ decay width are used to further constrain the model parameter space. Next, the production of new coloured fermionic mediators is investigated in a model of scalar, flavoured dark matter. Experimental results from signals characterized by final state jets and missing transverse energy, resulting from mediator pair production and subsequent decay to a quark and the dark matter particle, are used to constrain the mediator mass. A Higgs portal model is also considered, with the addition of a scalar singlet field that mixes with the SM Higgs. The constraints from current LHC Higgs data are established, and prospective signatures at the proposed International Linear Collider (ILC) are investigated; the discovery potential in the remaining allowed parameter space is explored, through precision measurement in double Higgs production. Finally, a scalar extension is also applied to a DM model with two additional scalar mediators, in a model that is motivated by the galactic centre (GC) gamma ray excess seen in data from the Fermi Large Area Telescope. Results from LHC Higgs searches and measurements are used to constrain the scalar parameters in a benchmark model that was fit to the GC excess." --

Author: Gabriel Zsembinszki
Publisher: LAP Lambert Academic Publishing
ISBN: 9783659273452
Category :
Languages : en
Pages : 276

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The most successful scientific theory today about the origin and evolution of the universe is known as the standard Big Bang model, which is one of the most ambitious intellectual constructions of the humanity. It is based on two consolidated branches of theoretical physics, namely, the theory of General Relativity and the Standard Model of particle physics, and is able to make robust predictions, some of them being already confirmed by very precise observations. However, this model is not able to explain some questions raised by observational evidence, such as early inflation of the universe, dark matter and dark energy. This book makes an overview of some of the features of the standard cosmology, and also includes a few original models proposed to solve some of the shortcomings of the standard cosmology, as possible extensions of the Big Bang model. The models, published as articles in scientific journals, introduce new symmetries, fields and particles in order to explain inflation, dark energy and dark matter, separately or in a unified description. The book is addressed especially to PhD students, but also to anyone who is interested in cosmology and astroparticle theory.