| 1. |
- Catena, Riccardo, 1978, et al.
(author)
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Crystal responses to general dark matter-electron interactions
- 2021
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In: Physical Review Research. - 2643-1564. ; 3:3
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Journal article (peer-reviewed)abstract
- We develop a formalism to describe the scattering of dark matter (DM) particles by electrons bound in crystals for a general form of the underlying DM-electron interaction. Such a description is relevant for direct-detection experiments of DM particles lighter than a nucleon, which might be observed in operating DM experiments via electron excitations in semiconductor crystal detectors. Our formalism is based on an effective theory approach to general nonrelativistic DM-electron interactions, including the anapole, and magnetic and electric dipole couplings, combined with crystal response functions defined in terms of electron wave function overlap integrals. Our main finding is that, for the usual simplification of the velocity integral, the rate of DM-induced electronic transitions in a semiconductor material depends on at most five independent crystal response functions four of which are distinct from the usual scalar response. We identify these crystal responses and evaluate them using density functional theory for crystalline silicon and germanium, which are used in operating DMdirect-detection experiments. Our calculations allow us to set 90% confidence level limits on the strength of DM-electron interactions from data reported by the SENSEI and EDELWEISS experiments. The crystal response functions discovered in this paper encode properties of crystalline solids that do not interact with conventional experimental probes, suggesting the use of the DM wind as a probe to reveal new kinds of hidden order in materials.
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| 2. |
- Catena, Riccardo, 1978, et al.
(author)
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Dark matter-electron interactions in materials beyond the dark photon model
- 2023
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In: Journal of Cosmology and Astroparticle Physics. - : IOP Publishing. - 1475-7516. ; 2023:3
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Journal article (peer-reviewed)abstract
- The search for sub-GeV dark matter (DM) particles via electronic transitions in underground detectors attracted much theoretical and experimental interest in the past few years. A still open question in this field is whether experimental results can in general be interpreted in a framework where the response of detector materials to an external DM probe is described by a single ionisation or crystal form factor, as expected for the so-called dark photon model. Here, ionisation and crystal form factors are examples of material response functions: interaction-specific integrals of the initial and final state electron wave functions. In this work, we address this question through a systematic classification of the material response functions induced by a wide range of models for spin-0, spin-1/2 and spin-1 DM. We find several examples for which an accurate description of the electronic transition rate at DM direct detection experiments requires material response functions that go beyond those expected for the dark photon model. This concretely illustrates the limitations of a framework that is entirely based on the standard ionisation and crystal form factors, and points towards the need for the general response-function-based formalism we pushed forward recently [1,2]. For the models that require non-standard atomic and crystal response functions, we use the response functions of [1,2] to calculate the DM-induced electronic transition rate in atomic and crystal detectors, and to present 90% confidence level exclusion limits on the strength of the DM-electron interaction from the null results reported by XENON10, XENON1T, EDELWEISS and SENSEI.
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| 3. |
- Catena, Riccardo, 1978, et al.
(author)
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Direct searches for general dark matter-electron interactions with graphene detectors: Part I. Electronic structure calculations
- 2023
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In: Physical Review Research. - 2643-1564. ; 5:4
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Journal article (peer-reviewed)abstract
- We develop a formalism to describe electron ejections from graphenelike targets by dark matter (DM) scattering for general forms of scalar and spin-1/2 DM-electron interactions, and we compare their applicability and accuracy within the density functional theory (DFT) and tight-binding (TB) approaches. This formalism allows for accurate prediction of the daily modulation signal expected from DM in upcoming direct detection experiments employing graphene sheets as the target material. A key result is that the physics of the graphene sheet and that of the DM and the ejected electron factorize, allowing for the rate of ejections from all forms of DM to be obtained with a single graphene response function. We perform a comparison between the TB and DFT approaches to modeling the initial state electronic wave function within this framework, with DFT emerging as the more self-consistent and reliable choice due to the challenges in the embedding of an appropriate atomic contribution into the TB approach.
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| 4. |
- Catena, Riccardo, 1978, et al.
(author)
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Direct searches for general dark matter-electron interactions with graphene detectors: Part II. Sensitivity studies
- 2023
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In: Physical Review Research. - 2643-1564. ; 5:4
-
Journal article (peer-reviewed)abstract
- We use a formalism that describes electron ejections from graphenelike targets by dark matter (DM) scattering for general forms of scalar and spin-1/2 DM-electron interactions in combination with state-of-the-art density functional calculations to produce predictions and reach estimates for various possible carbon-based detector designs. Our results indicate the importance of a proper description of the target electronic structure. In addition, we find a strong dependence of the predicted observed signal for different DM candidate masses and interaction types on the detailed geometry and design of the detector. Combined with directional background vetoing, these dependencies will enable the identification of DM particle properties once a signal has been established.
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| 5. |
- Urdshals, Einar, 1995
(author)
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Crystal responses to general dark matter-electron interactions
- 2022
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In: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 2156:1
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Conference paper (peer-reviewed)abstract
- In [1] we develop a non-relativistic effective field theory (NR-EFT) based framework with which rates of dark matter (DM) induced electron hole pair creation in silicon and germanium crystals can be obtained for any form of non-relativistic DM-electron interactions with spin 1/2 DM. We find that the crystal physics is captured by 5 crystal response functions, 4 of which are novel to that work, and we evaluate them using a state of the art DFT calculation.
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| 6. |
- Urdshals, Einar, 1995
(author)
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Dark matter electron interactions in detector materials
- 2023
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Licentiate thesis (other academic/artistic)abstract
- Dark Matter (DM) makes up 85% of the matter content of the universe, and its gravitational effects are seen on scales ranging from that of cosmology to that of galactic astrophysics. The nature of DM is, however, unknown. Studying DM in the lab is key to understanding its nature. For decades, experiments have been attempting to do this through searches for DM induced nuclear recoils. These have not been found, and a possible reason for this is that the hypothetical DM particle is too light to induce nuclear recoils. Therefore, in the last decade experiments have been built to study DM through electron recoils instead. As the electron is 4 orders of magnitude lighter than the nucleus, electron recoils can be induced by DM down to 4 orders of magnitude lighter than the lightest DM particle probeable with nuclear recoils. In order to understand current and upcoming results from experiments searching for DM induced electron recoils, a theoretical understanding of DM electron scatterings in detector materials is needed. This requires input both from dark matter and material physics, and so far DM electron interactions have only been studied within the dark photon model. In the dark photon model, the DM-electron scattering takes a relatively simple form, and the material responds to the scattering through a single "response function". Relaxing the assumption of the dark photon model, and instead applying Non-Relativistic Effective Theory approach, we calculate the expected detector signature for a wide range of DM models in Silicon and Germanium. In the papers of this thesis, we find that in contrast to the single response function produced by the dark photon model, the material can respond with 7 different response functions. These novel response functions we show to generically arise in a wide range of DM-electron interactions. As such, the papers of this thesis vastly extends the forms of DM-electron interactions that can be studied in Silicon and Germanium based experiments. These interactions made studyable by the works underlying this thesis are not fringe cases, but generically arise in a wide range of models. To illustrate this we consider a range of simplified models with a DM particle with spin 0, spin 1/2 and spin 1.
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| 7. |
- Urdshals, Einar, 1995
(author)
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Dark matter electron interactions in detector materials
- 2024
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Doctoral thesis (other academic/artistic)abstract
- Dark Matter (DM) makes up 85% of the matter content of the universe, and its gravitational effects are seen on scales ranging from that of cosmology to that of galactic astrophysics. The nature of DM is, however, unknown. Study- ing DM in the lab with a class of experiments called direct detection (DD) experiments is key to understanding its properties. For decades, experiments have been attempting to do this through searches for DM induced nuclear recoils. These have not been found, and a possible reason for this is that the hypothetical DM particle is too light to induce nuclear recoils. Therefore, in the last decade experiments have been built to study DM through electron recoils instead. As the electron is 4 orders of magnitude lighter than the nu- cleus, electron recoils can be induced by DM down to 4 orders of magnitude lighter than the lightest DM particle probeable with nuclear recoils. In order to understand current and upcoming results from experiments searching for DM induced electron recoils, a theoretical understanding of DM electron scatterings in detector materials is needed. When modelling such electron interactions, one need input both from DM and material physics. This thesis improves the theoretical understanding by both improving the material description using density functional theory (DFT), and by extending the DM description using non-relativistic effective theory (NR-EFT) tools. The improvement gives not only a more accurate description of the DM- electron interactions that the experiments are expected to see; it also vastly extends the forms of DM that can be studied in direct detection experiments. Before this extension, one typically focused on a benchmark case of DM, the so called dark photon model. With this extension, one can cover all forms of gravitationally bound DM with spins of 0, 1/2 or 1. In the included works, advances are made in the description of DM-electron interactions in common detector materials such as liquid xenon, silicon and germanium, as well as to materials in the research and development phase, such as graphene and carbon nanotubes (CNTs).
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