arXiv subjects

Joerg Jaeckel

Publications and source records attributed to Joerg Jaeckel.

At least 73 records · Page 4Linked to original sources

arXiv2019

Exploring High Multiplicity Amplitudes: The QM Analogue of the Spontaneously Broken Case

Calculations of high multiplicity Higgs amplitudes exhibit a rapid growth that may signal an end of perturbative behavior or even the need for new physics phenomena. As a step towards this problem we consider the quantum mechanical equivalent of $1 \to n$ scattering amplitudes in a spontaneously broken $ϕ^4$-theory by extending our previous results on the quartic oscillator with a single minimum to transitions $\langle n \lvert \hat{x} \rvert 0 \rangle$ in the symmetric double-well potential with quartic coupling $λ$. Using recursive techniques to high order in perturbation theory, we argue that these transitions are of exponential form $\langle n \lvert \hat{x} \rvert 0 \rangle \sim \exp \left( F (λn) / λ\right)$ in the limit of large $n$ and $λn$ fixed. We apply the methods of "exact perturbation theory" put forward by Serone et al. to obtain the exponent $F$ and investigate its structure in the regime where tree-level perturbation theory violates unitarity constraints. We find that the resummed exponent is in agreement with unitarity and rigorous bounds derived by Bachas.

hep-ph↗

arXiv2018

Lightish but clumpy: scalar dark matter from inflationary fluctuations

It has recently been shown [1] that light vector particles produced from inflationary fluctuations can give rise to the dark matter in the Universe. A similar mechanism has been discussed in [2] for a non-minimally coupled scalar enjoying a Higgs portal interaction. We discuss in detail how such a generation of dark matter works in a minimal setup of a massive scalar non-minimally coupled to gravity. For suitable values of the non-minimal coupling any initial constant value of the field is suppressed during inflation. At the same time, the quantum fluctuations acquired during inflation give rise to a peaked energy density power spectrum. Isocurvature constraints can be avoided since nearly all of the energy is concentrated in fluctuations too small to be observed in the CMB. For masses $\gtrsim {\rm eV}$ and sufficiently high inflation scale the energy contained in these fluctuations is sufficient to account for the cold dark matter of the Universe. At small scales $\ell_{\rm today}\sim 10^{4}\,{\rm km}\sqrt{m/{\rm eV}}\sim 10^{-4}\,{\rm AU}\sqrt{m/{\rm eV}}$ fluctuations are large and we therefore expect a rather clumpy nature of this form of dark matter.

hep-ph↗

arXiv2018

Exploring High Multiplicity Amplitudes in Quantum Mechanics

Calculations of $1\to N$ amplitudes in scalar field theories at very high multiplicities exhibit an extremely rapid growth with the number $N$ of final state particles. This either indicates an end of perturbative behaviour, or possibly even a breakdown of the theory itself. It has recently been proposed that in the Standard Model this could even lead to a solution of the hierarchy problem in the form of a "Higgsplosion". To shed light on this question we consider the quantum mechanical analogue of the scattering amplitude for $N$ particle production in $ϕ^4$ scalar quantum field theory, which corresponds to transitions $\langle N \lvert \hat{x} \rvert 0 \rangle$ in the anharmonic oscillator with quartic coupling $λ$. We use recursion relations to calculate the $\langle N \lvert \hat{x} \rvert 0 \rangle$ amplitudes to high order in perturbation theory. Using this we provide evidence that the amplitude can be written as $\langle N \lvert \hat{x} \rvert 0 \rangle \sim \exp(F(λN)/λ)$ in the limit of large $N$ and $λN$ fixed. We go beyond the leading order and provide a systematic expansion in powers of $1/N$. We then resum the perturbative results and investigate the behaviour of the amplitude in the region where tree-level perturbation theory violates unitarity constraints. The resummed amplitudes are in line with unitarity as well as stronger constraints derived by Bachas. We generalize our result to arbitrary states and powers of local operators $\langle N \lvert \hat{x}^q \rvert M \rangle$ and confirm that, to exponential accuracy, amplitudes in the large $N$ limit are independent of the explicit form of the local operator, i.e. in our case $q$.

hep-ph↗

arXiv2018

Exploring ALPs beyond the canonical

Axion-like particles (ALPs) are interesting dark matter candidates both from the theoretical as well as from the experimental perspective. Usually they are motivated as pseudo-Nambu-Goldstone bosons. In this case one of their most important features is that their coupling to other particles is suppressed by a large scale, the vacuum expectation value of the field breaking the symmetry that gives rise to them. This naturally endows them with very weak interactions but also restricts the maximal field value and therefore the regions where sufficient dark matter is produced. In this paper we investigate deviations from this simplest setup, where the potential and interactions are as expected for a pseudo-Nambu-Goldstone boson, but the kinetic term has singularities. This leads to a significantly increased area in parameter space where such particles can be dark matter and can be probed by current and near future experiments. We discuss cosmological limits and in the course of this give a simple derivation of a formula for isocurvature fluctuations in models with general anharmonic potentials. As an application of this formula we give an update of the isocurvature constraints for QCD axion dark matter models, using the most recent results for the QCD topological susceptibility and the newest Planck data.

hep-ph↗

arXiv2017

QCD axions and axionlike particles in a two-inflation scenario

We investigate the phenomenology of QCD axions and axionlike particles in a scenario with two eras of inflation. In particular, we describe the possible solutions for the QCD axion field equation after the second inflation and reheating. We calculate the dilution numerically for QCD axions and give an analytic approximation for axionlike particles. While it has been realised before that such a scenario can dilute the axion energy density and open up the parameter space for the axion decay constant $f_A$, we find that even a small increase in the relative QCD axion energy density is possible.

hep-ph↗

arXiv2017

Towards the fate of the oscillating false vacuum

Motivated by cosmological examples we study quantum field theoretical tunnelling from an initial state where the "classical field", i.e. the vacuum expectation value of the field operator is spatially homogeneous but performing a time-dependent oscillation about a local minimum. In particular we estimate both analytically and numerically the exponential contribution to the tunnelling probability. We additionally show that after the tunnelling event, the classical field solution - the so-called "bubble" - mediating the phase transition can either grow or collapse. We present a simple analytical criterium to distinguish between the two behaviours.

hep-ph↗

arXiv2017

Purely flavor-changing Z' bosons and where they might hide

A plethora of ultraviolet completions of the Standard Model have extra U(1) gauge symmetries. In general, the associated massive $Z^\prime$ gauge boson can mediate flavor-changing neutral current processes at tree level. We consider a situation where the $Z^\prime$ boson couples solely via flavor-changing interactions to quarks and leptons. In this scenario the model parameter space is, in general, quite well constrained by existing flavor bounds. However, we argue that cancellation effects shelter islands in parameter space from strong flavor constraints and that these can be probed by multipurpose collider experiments like ATLAS or CMS as well as LHCb in upcoming runs at the LHC. In still allowed regions of parameter space these scenarios may help to explain the current tension between theory and experiment of $(g-2)_μ$ as well as a small anomaly in $τ$ decays.

hep-ph↗

arXiv2017

Dish Antenna Searches for WISPy Dark Matter: Directional Resolution Small Mass Limitations

Hidden photon and axion-like dark matter may be detected using spherical reflective surfaces such as dish antenna setups converting some of the dark matter particles into photons and concentrating them on a detector. These setups may be used to perform directional searches measuring the dark matter momentum distribution. We briefly review the photon distribution one expects to detect with such an antenna and directional resolution in ray approximation. Furthermore we consider the regime $m_{DM} \lesssim (R_{sp}\,v_{DM})^{-1}$ where this approximation does not hold anymore due to the photon wavelength exceeding the expected distribution widths. We discuss how this affects the expected distributions and experimental implications.

hep-ph↗

arXiv2017

Getting Stuck: Using Monosignatures to Test Highly Ionizing Particles

In this paper we argue that monojet and monophoton searches can be a sensitive test of very highly ionizing particles such as particles with charges $\gtrsim 150e$ and more generally particles that do not reach the outer parts of the detector. 8 TeV monojet data from the CMS experiment excludes such objects with masses in the range $\lesssim 650~{\text{GeV}}$ and charges $\gtrsim 100e$. This nicely complements searches for highly ionizing objects at ALICE, ATLAS, CMS and LHCb. Expected improvements in these channels will extend the sensitivity range to $m\lesssim 750~{\text{GeV}}$. This search strategy can directly be generalized to other particles that strongly interact with the detector material, such as e.g. magnetic monopoles.

hep-ph↗

arXiv2016

Hearing the signals of dark sectors with gravitational wave detectors

Motivated by aLIGO's recent discovery of gravitational waves we discuss signatures of new physics that could be seen at ground and space-based interferometers. We show that a first order phase transition in a dark sector would lead to a detectable gravitational wave signal at future experiments, if the phase transition has occurred at temperatures few orders of magnitude higher than the electroweak scale. The source of gravitational waves in this case is associated with the dynamics of expanding and colliding bubbles in the early universe. At the same time we point out that topological defects, such as dark sector domain walls, may generate a detectable signal already at aLIGO. Both -- bubble and domain wall -- scenarios are sourced by semi-classical configurations of a dark new physics sector. In the first case the gravitational wave signal originates from bubble wall collisions and subsequent turbulence in hot plasma in the early universe, while the second case corresponds to domain walls passing through the interferometer at present and is not related to gravitational waves. We find that aLIGO at its current sensitivity can detect smoking-gun signatures from domain wall interactions, while future proposed experiments including the fifth phase of aLIGO at design sensitivity can probe dark sector phase transitions.

hep-ph↗

arXiv2016

Gravitational Waves from Axion Monodromy

Large field inflation is arguably the simplest and most natural variant of slow-roll inflation. Axion monodromy may be the most promising framework for realising this scenario. As one of its defining features, the long-range polynomial potential possesses short-range, instantonic modulations. These can give rise to a series of local minima in the post-inflationary region of the potential. We show that for certain parameter choices the inflaton populates more than one of these vacua inside a single Hubble patch. This corresponds to a dynamical phase decomposition, analogously to what happens in the course of thermal first-order phase transitions. In the subsequent process of bubble wall collisions, the lowest-lying axionic minimum eventually takes over all space. Our main result is that this violent process sources gravitational waves, very much like in the case of a first-order phase transition. We compute the energy density and peak frequency of the signal, which can lie anywhere in the mHz-GHz range, possibly within reach of next-generation interferometers. We also note that this "dynamical phase decomposition" phenomenon and its gravitational wave signal are more general and may apply to other inflationary or reheating scenarios with axions and modulated potentials.

hep-ph↗

arXiv2016

Monodromy Dark Matter

Light pseudo-Nambu-Goldstone bosons (pNGBs) such as, e.g.~axion-like particles, that are non-thermally produced via the misalignment mechanism are promising dark matter candidates. An important feature of pNGBs is their periodic potential, whose scale of periodicity controls all their couplings. As a consequence of the periodicity the maximal potential energy is limited and, hence, producing the observed dark matter density poses significant constraints on the allowed masses and couplings. In the presence of a monodromy, the field range as well as the range of the potential can be significantly extended. As we argue in this paper this has important phenomenological consequences. The constraints on the masses and couplings are ameliorated and couplings to Standard Model particles could be significantly stronger, thereby opening up considerable experimental opportunities. Yet, monodromy models can also give rise to new and qualitatively different features. As a remnant of the periodicity the potential can feature pronounced wiggles. When the field is passing through them quantum fluctuations are enhanced and particles with non-vanishing momentum are produced. Here, we perform a first analysis of this effect and delineate under which circumstances this becomes important. We discuss possible cosmological consequences.

hep-ph↗

arXiv2016

Hidden Photons in Aharonov-Bohm-Type Experiments

We discuss the Aharonov-Bohm effect in the presence of hidden photons kinetically mixed with the ordinary electromagnetic photons. The hidden photon field causes a slight phase shift in the observable interference pattern. It is then shown how the limited sensitivity of this experiment can be largely improved. The key observation is that the hidden photon field causes a leakage of the ordinary magnetic field into the supposedly field-free region. The direct measurement of this magnetic field can provide a sensitive experiment with a good discovery potential, particularly below the $\sim$ meV mass range for hidden photons.

hep-ph↗

arXiv2016

ALPtraum: ALP production in proton beam dump experiments

With their high beam energy and intensity, existing and near-future proton beam dumps provide an excellent opportunity to search for new very weakly coupled particles in the MeV to GeV mass range. One particularly interesting example is a so-called axion-like particle (ALP), i.e. a pseudoscalar coupled to two photons. The challenge in proton beam dumps is to reliably calculate the production of the new particles from the interactions of two composite objects, the proton and the target atoms. In this work we argue that Primakoff production of ALPs proceeds in a momentum range where production rates and angular distributions can be determined to sufficient precision using simple electromagnetic form factors. Reanalysing past proton beam dump experiments for this production channel, we derive novel constraints on the parameter space for ALPs. We show that the NA62 experiment at CERN could probe unexplored parameter space by running in 'dump mode' for a few days and discuss opportunities for future experiments such as SHiP.

hep-ph↗

arXiv2015

Directional Resolution of Dish Antenna Experiments to Search for WISPy Dark Matter

Dark matter consisting of very light and very weakly interacting particles such as axions, axion-like particles and hidden photons could be detected using reflective surfaces. On such reflectors some of the dark matter particles are converted into photons and, given a suitable geometry, concentrated on the detector. This technique offers sensitivity to the direction of the velocity of the dark matter particles. In this note we investigate how far spherical mirrors can concentrate the generated photons and what this implies for the resolution in directional detection as well as the sensitivity of discovery experiments not aiming for directional resolution. Finally we discuss an improved setup using a combination of a reflecting plane with focussing optics.

hep-ph↗

arXiv2015

Musings on cosmological relaxation and the hierarchy problem

Recently Graham, Kaplan and Rajendran [1] proposed cosmological relaxation as a mechanism for generating a hierarchically small Higgs vacuum expectation value. Inspired by this we collect some thoughts on steps towards a solution to the electroweak hierarchy problem and apply them to the original model of cosmological relaxation [1]. To do so, we study the dynamics of the model and determine the relation between the fundamental input parameters and the electroweak vacuum expectation value. Depending on the input parameters the model exhibits three qualitatively different regimes, two of which allow for hierarchically small Higgs vacuum expectation values. One leads to standard electroweak symmetry breaking whereas in the other regime electroweak symmetry is mainly broken by a Higgs source term. While the latter is not acceptable in a model based on the QCD axion, in non-QCD models this may lead to new and interesting signatures in Higgs observables.

hep-ph↗

arXiv2015

The FUNK search for Hidden Photon Dark Matter in the eV range

We give a brief update on the search for Hidden Photon Dark Matter with FUNK. The experiment uses a large spherical mirror, which, if Hidden Photon Dark Matter exists in the accessible mass and coupling parameter range, would yield an optical signal in the mirror's center in an otherwise dark environment. After a test run with a CCD, preparations for a run with a low-noise PMT are under way and described in this proceedings.

physics.ins-det↗

arXiv2015

Search for dark matter in the hidden-photon sector with a large spherical mirror

If dark matter consists of hidden-sector photons which kinetically mix with regular photons, a tiny oscillating electric-field component is present wherever we have dark matter. In the surface of conducting materials this induces a small probability to emit single photons almost perpendicular to the surface, with the corresponding photon frequency matching the mass of the hidden photons. We report on a construction of an experimental setup with a large ~14 m2 spherical metallic mirror that will allow for searches of hidden-photon dark matter in the eV and sub-eV range by application of different electromagnetic radiation detectors. We discuss sensitivity and accessible regions in the dark matter parameter space.

astro-ph.IM↗