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Rainer Dick

Publications and source records attributed to Rainer Dick.

At least 19 recordsLinked to original sources
arXiv2026

Photon localization: a comparative study

We compare different measures for photon localization in terms of two-dimensional Gaussian wave packets. We find that all measures start to coalesce if the wave packet has evolved for times which are larger than a few times the inverse momentum-space width of the package. However, the Landau-Peierls wave function yields the largest positive offset -ct>0 while the scalar Fourier transform of the wave packet yields the smallest offset and converges towards -ct=0 fastest. We also discuss local detection of photons through a model detector consisting of ions in ion traps. The position-dependent detection probabilities are inferred from the scattering matrix. We find that the local detection probability for photons can be expressed in terms of three of the proposed localization measures, viz. the Landau-Peierls wave function, the energy wave function, and the Hawton density. Those three porposals also remain close throughout the time evolution of the single-photon wave packet.

quant-ph↗
arXiv2025

Symmetric tensor portals to dark matter I: Creation of dark scalars

We examine the creation of scalar dark matter through a symmetric tensor portal. We find that both freeze-in and thermal freeze-out through a symmetric tensor mediator can create scalar dark matter. The required tensor masses for freeze-in are much larger than for freeze-out for the same dark-matter mass, in agreement with the nonthermalization assumption in freeze-in scenarios.

hep-ph↗
arXiv2024

Antisymmetric tensor portals to dark matter

Both freeze-in of very weakly coupled dark matter and freeze-out of initially thermalized dark matter from the primordial heat bath provide interesting possibilities for dark matter creation in the early universe. Both scenarios allow for a calculation of baryon-dark matter coupling constants as a function of dark matter mass due to the constraint that freeze-in or freeze-out produce the observed dark matter abundance. Here we compare the resulting coupling constants in the two scenarios if dark matter couples to baryons through an antisymmetric tensor portal. The freeze-in scenario predicts much smaller coupling in agreement with the nonthermalization postulate. We find that the couplings as a function of mass behave very differently in the two scenarios.

hep-ph↗
arXiv2024

Back to Bohr: Quantum Jumps in Schroedinger's Wave Mechanics

The measurement problem of quantum mechanics concerns the question under which circumstances coherent wave evolution becomes disrupted to produce eigenstates of observables, instead of evolving superpositions of eigenstates. The problem needs to be addressed already within wave mechanics, before second quantization, because low-energy interactions can be dominated by particle-preserving potential interactions. We discuss a scattering array of harmonic oscillators which can detect particles penetrating the array through interaction with a short-range potential. Evolution of the wave function of scattered particles, combined with Heisenberg's assertion that quantum jumps persist in wave mechanics, indicates that the wave function will collapse around single oscillator sites if the scattering is inelastic, while it will not collapse around single sites for elastic scattering. The Born rule for position observation is then equivalent to the statement that the wave function for inelastic scattering amounts to an epistemic superposition of possible scattering states, in the sense that it describes a sum of probability amplitudes for inelastic scattering off different scattering centers, whereas at most one inelastic scattering event can happen at any moment in time. Within this epistemic interpretation of the wave function, the actual underlying inelastic scattering event corresponds to a quantum jump, whereas the continuously evolving wave function only describes the continuous evolution of probability amplitudes for scattering off different sites. Quantum jumps then yield definite position observations as defined by the spatial resolution of the oscillator array.

quant-ph↗
arXiv2024

Photon emission from macroscopic currents

Coherent states are a well-established tool of quantum optics to describe electromagnetic waves in terms of photons. However, they do not describe the near-field regime of radiation sources. Instead, we generically use classical solutions of Maxwell's equations to describe radiation in the near-field regime. The classical solutions provide linear relations between currents and emitted electromagnetic fields, whereas evolution of states at the quantum level proceeds through unitary time evolution operators involving photon operators. This begs questions how the classical radiation equations relate to unitary quantum evolution, and how we can describe macroscopic fields from antennas or magnetic coils in terms of elementary photons. The present paper answers both questions through the construction of generalized Glauber states for radiation emitters.

quant-ph↗
arXiv2024

Collapse of wave functions in Schroedinger's wave mechanics

We show that inelastic scattering leads to a collapse of the wave function within standard evolution through the Schroedinger equation, whereas elastic scattering will not collapse the wave function. Specifically, we find that the initial width of the emerging wave function in inelastic scattering is primarily determined by the size of the participating scattering center, but not by the width of the incoming wave function. This implies that dynamical collapse of the wave function through inelastic scattering, together with energy quantization in bound quantum systems, can explain the emergence of particle-like signals without the need to invoke the Born rule.

physics.gen-ph↗
arXiv2023

Relativistic probability densities for location

Imposing the Born rule as a fundamental principle of quantum mechanics would require the existence of normalizable wave functions also for relativistic particles. Indeed, the Fourier transforms of normalized k-space amplitudes yield normalized x-space wave packets which reproduce the standard k-space expectation values for energy and momentum from local momentum pseudo-densities. However, in the case of bosonic fields, the wave packets are nonlocally related to the corresponding relativistic quantum fields, and therefore the canonical local energy-momentum densities differ from the pseudo-densities and appear nonlocal in terms of the wave packets. We examine the relation between the canonical energy density, the canonical charge density, the energy pseudo-density, and the Born density for the massless free Klein-Gordon field. We find that those four proxies for particle location are tantalizingly close even in this extremely relativistic case: In spite of their nonlocal mathematical relations, they are mutually local in the sense that their maxima do not deviate beyond a common position uncertainty $\Delta x$. Indeed, they are practically indistinguishable in cases where we would expect a normalized quantum state to produce particle-like position signals, viz. if we are observing quanta with momenta $p\gg\Delta p\ge\hbar/2\Delta x$. We also translate our results to massless Dirac fields. Our results confirm and illustrate that the normalized energy density provides a suitable measure for positions of bosons, whereas normalized charge density provides a suitable measure for fermions.

quant-ph↗
arXiv2021

Constraints on antisymmetric tensor fields from Bhabha scattering

Antisymmetric tensor fields are a compelling prediction of string theory. This makes them an interesting target for particle physics because antisymmetric tensors may couple to electromagnetic dipole moments, thus opening a possible discovery opportunity for string theory. The strongest constraints on electromagnetic dipole couplings would arise from couplings to electrons, where these couplings would contribute to Moller and Bhabha scattering. Previous measurements of Bhabha scattering constrain the couplings to $\tilde{M}_e m_C>7.1\times 10^4\,\mathrm{GeV}^2$, where $m_C$ is the mass of the antisymmetric tensor field and $\tilde{M}_e$ is an effective mass scale appearing in the electromagnetic dipole coupling.

hep-ph↗
arXiv2018

The shadow of dark matter as a shadow of string theory

We point out that string theory can solve the conundrum to explain the emergence of an electroweak dipole moment from electroweak singlets through induction of those dipole moments through a Kalb-Ramond dipole coupling. This can generate a U_Y(1) portal to dark matter and entails the possibility that the U_Y(1) gauge field is related to a fundamental vector field for open string interactions. The requirement to explain the observed dark matter abundance relates the coupling scale in the corresponding low-energy effective U_Y(1) portal to the dark matter mass. The corresponding electron recoil cross sections for a single dipole coupled dark matter species are generically below the current limits from XENON, SuperCDMS and SENSEI, except in the GeV mass range if the electric dipole coupling becomes stronger than the magnetic coupling. Furthermore, the recoil cross sections are above the neutrino floor and the U_Y(1) portal can be tested with longer exposure or larger detectors. Discovery of electroweak dipole dark matter would therefore open an interesting window into string phenomenology.

hep-ph↗
arXiv2018

Direct signals from electroweak singlets through the Higgs portal

We review predictions and constraints for nuclear recoil signals from Higgs portal dark matter under the assumption of standard thermal creation from freeze-out. Thermally created scalar and vector Higgs portal dark matter masses are constrained to be in the resonance region near half the Higgs mass or above several TeV. The resonance region for these models will be tested by XENONnT and LZ. The full mass range up to the unitarity limit can be tested by DarkSide-20k and DARWIN. Fermionic Higgs portal dark matter with a pure CP odd coupling is constrained by the Higgs decay width, but has strongly suppressed recoil cross sections which cannot be tested with upcoming experiments. Fermionic Higgs portal dark matter with a combination of CP even and odd Higgs couplings can be constrained by the direct search experiments.

hep-ph↗
arXiv2017

Dynamical alignment of visible and dark sector gauge groups

We discuss a dark family of lepton-like particles with their own "private" gauge bosons under a local SU'(2)xU'(1) symmetry. The product of dark and visible gauge groups SU'(2)xU'(1)xSU_w(2)xU_Y(1) is broken dynamically to the diagonal (vector-like) subgroup SU(2)xU(1) through the coupling of two scalar fields M_i to the Higgs field and the dark lepton-like particles. After substituting vacuum expectation values for the fields M_i, the Higgs doublet couples in the standard way to the left-handed SU'(2) doublet and right-handed singlets of the dark gauge group, but not to the extra gauge bosons. This defines a new Higgs portal, where the "dark leptons" can contribute to the dark matter and interact with Standard Model matter through Higgs exchange. It also defines a dark matter model with internal interactions. At low energies, the Standard Model Higgs boson aligns the two electroweak-type symmetry groups in the visible and dark sectors and generates the masses in both sectors. We also identify charge assignments in the dark sector which allow for the formation of dark atoms as bound states of dark lepton-like particles. The simplest single-component dark matter version of the model predicts a dark matter mass around 96 GeV, but the corresponding nucleon recoil cross section is ruled out by the xenon based experiments. However, multi-component models or models with a dark SU'(2) doublet mediator instead of the Higgs portal would still be viable.

hep-ph↗
arXiv2017

Quantum jumps, superpositions, and the continuous evolution of quantum states

The apparent dichotomy between quantum jumps on the one hand, and continuous time evolution according to wave equations on the other hand, provided a challenge to Bohr's proposal of quantum jumps in atoms. Furthermore, Schroedinger's time-dependent equation also seemed to require a modification of the explanation for the origin of line spectra due to the apparent possibility of superpositions of energy eigenstates for different energy levels. Indeed, Schroedinger himself proposed a quantum beat mechanism for the generation of discrete line spectra from superpositions of eigenstates with different energies. However, these issues between old quantum theory and Schroedinger's wave mechanics were correctly resolved only after the development and full implementation of photon quantization. The second quantized scattering matrix formalism reconciles quantum jumps with continuous time evolution through the identification of quantum jumps with transitions between different sectors of Fock space. The continuous evolution of quantum states is then recognized as a sum over continually evolving jump amplitudes between different sectors in Fock space. In today's terminology, this suggests that linear combinations of scattering matrix elements are epistemic sums over ontic states. Insights from the resolution of the dichotomy between quantum jumps and continuous time evolution therefore hold important lessons for modern research both on interpretations of quantum mechanics and on the foundations of quantum computing. They demonstrate that discussions of interpretations of quantum theory necessarily need to take into account field quantization. They also demonstrate the limitations of the role of wave equations in quantum theory, and caution us that superpositions of quantum states for the formation of qubits may be more limited than usually expected.

physics.hist-ph↗
arXiv2016

Remarks on Top-philic $Z^\prime$ Boson Interactions with Nucleons

This article provides the calculation of an effective vertex function between a nucleon and a $Z^\prime$ boson that couples preferentially to either the top quark or the third generation of fermions, for the purpose of calculating vector-portal dark matter nuclear recoil cross sections. Mixing effects between the new gauge group $U(1)^\prime$ and the Standard Model hypercharge group $U(1)_Y$ are taken into account. Contributions to the $U(1)^\prime$ nucleon current from heavy quarks are quantified using the heavy quark expansion. Also taken into account are contributions from the 1-loop $Z^\prime$-gluon interactions and mixing-induced contributions from the light quarks in the nucleon. We find that, for reasonable values of the $U(1)^\prime$ gauge parameter, contributions from the light quarks dominate despite being mixing-suppressed. It is shown that this holds for most models even if mixing effects do not appear at tree level. Contributions from the heavy quarks and gluons are suppressed by $1/m_Q^2$ and possibly also by momentum in the low momentum transfer limits relevant for dark matter direct detection. We discuss under which conditions the subdominant terms become relevant.

hep-ph↗
arXiv2016

Detection prospects for conformally constrained vector-portal dark matter

We work with a UV conformal U(1)' extension of the Standard Model, motivated by the hierarchy problem and recent collider anomalies. This model admits fermionic vector portal WIMP dark matter charged under the U(1)' gauge group. The asymptotically safe boundary conditions can be used to fix the coupling parameters, which allows the observed thermal relic abundance to constrain the mass of the dark matter particle. This highly restricts the parameter space, allowing strong predictions to be made. The parameter space of several UV conformal U(1)' scenarios will be explored, and both bounds and possible signals from direct and indirect detection observation methods will be discussed.

hep-ph↗
arXiv2016

Gamma ray signals of the annihilation of Higgs-portal singlet dark matter

This article is an exploration of gamma ray signals of annihilating Higgs-portal singlet scalar and vector dark matter. Gamma ray signals are considered in the context of contributions from annihilations of singlets in the galactic halo to the Isotropic Gamma Ray Background (IGRB), in the context of the Galactic center excess, and in the context of observations of dwarf spheroidal galaxies. We find that Higgs-portal singlets of both species with a mass of $~$65 GeV can explain the Galactic center excess with reasonable accuracy, but that this mass range is in tension with current direct detection bounds. We also find that singlets in the mass range of 250-1000 GeV are consistent with both the Fermi-LAT IGRB observations and direct detection bounds. Additionally, bounds from gamma ray observations of the dwarf spheroidal galaxy Segue I are translated into bounds on the Higgs-portal couplings.

astro-ph.HE↗
arXiv2015

Crosstalk between DGP branes

If two DGP branes carry U(1) gauge theories and overlap, particles of one brane can interact with the photons from the other brane. This coupling modifies in particular the Coulomb potentials between charges from the same brane in the overlapping regions. The coupling also introduces Coulomb interactions between charges from the different branes which can generate exotic bound states. The effective modification of the fine structure constant in the overlap region generates a trough in signals at the redshift of the overlap region and an increase at smaller or larger redshift, depending on the value of the crosstalk parameter. This implies potentially observable perturbations in the Lyman-alpha forest if our 3-brane overlapped with another 3-brane in a region with redshift z<6. Crosstalk can also affect structure formation by enhancing or suppressing radiative cooling.

hep-th↗