80 research outputs found
How gravity shapes the low-energy frontier of particle physics
The Standard Model of particle physics and its implications for cosmology leave several fundamental questions unanswered, including the absence of CP violation in strong interactions and the origins of neutrino masses, dark matter, and dark energy. The most popular directions of model building beyond the Standard Model usually focus on new physics at short distances corresponding to high-energy scales. As an alternative direction, we present a novel class of low-energy solutions to the neutrino mass and strong CP problems at a new infrared gravitational scale, which is numerically coincident with the scale of dark energy. We demonstrate how a neutrino condensate, small neutrino masses, and an axion can emerge from a topological formulation of the chiral gravitational anomaly. First, we recapitulate how a gravitational θ-term leads to the emergence of a new bound neutrino state ην analogous to the η’ meson of QCD. On this basis, we show that a low-energy neutrino vacuum condensate forms and generates small neutrino masses. In the context of a follow-up model in which also the up-quark mass is generated by the neutrino condensate, we identify an axion that is composed entirely out of Standard Model fermion species: the η’ meson plus a minuscule admixture of the neutrino-composite ην boson. This new low-energy class of models has several unusual consequences for cosmology, astrophysics, gravity, and particle phenomenology. For example, we show that the cosmological neutrino mass bound vanishes due to a late cosmic phase transition in the neutrino sector. Moreover, we investigate the impact of the predicted topological defects and enhanced relic neutrino self-interactions on the dark matter and dark radiation content of the late Universe. On the astrophysics side, the key model prediction is the enhancement of neutrino decays observable in extraterrestrial neutrino fluxes. Concerning gravitational measurements, our models imply different polarization intensities of gravitational waves and a new attractive short-distance force among nucleons with a strength comparable to gravity. With regard to particle phenomenology, we explain potential signatures of flavor-violating processes, shining-light-through-walls signals, and possible sterile neutrinos in short-baseline experiments. We comment on how these model predictions can be tested with current and future experiments, in particular Euclid, IceCube, KATRIN, and PTOLEMY.Das Standardmodell der Teilchenphysik und seine kosmologischen Implikationen lassen einige fundamentale Fragen unbeantwortet, insbesondere die Abwesenheit von CP-Verletzung in der starken Wechselwirkung sowie die Ursprünge von Neutrinomassen, Dunkler Materie und Dunkler Energie. Innerhalb der Modellentwicklung jenseits des Standardmodells konzentrieren sich die populärsten Forschungsrichtungen üblicherweise auf neue Strukturen bei hohen Energien bzw. kleinen Abständen. Als eine alternative Richtung präsentieren wir in dieser Dissertation eine neue Klasse von niederenergetischen Lösungen der Neutrinomassen- und starken CP-Probleme. Diese Klasse manifestiert sich auf einer neuen infraroten Gravitationsskala, welche numerisch übereinstimmt mit der Skala der Dunklen Energie. Wir zeigen, wie sich ein Neutrinokondensat, kleine Neutrinomassen und ein Axion aus einer topologischen Formulierung der chiralen Gravitationsanomalie ergeben können. Zuerst rekapitulieren wir, wie ein gravitativer θ-Term zur Entstehung eines neuen gebundenen Neutrinozustands ην führt, analog zum η‘-Meson in der QCD. Auf dieser Basis leiten wir her, dass sich ein niederenergetisches Neutrino-Vakuumskondensat bildet, welches kleine Neutrinomassen generiert. Im Rahmen eines darauf aufbauenden Modells, in welchem auch die Masse des Up-Quarks durch das Neutrinokondensat erzeugt wird, identifizieren wir ein Axion, welches ausschließlich aus Fermionen des Standardmodells besteht: dem η‘-Meson plus einer winzigen Beimischung des ην-Bosons bestehend aus Neutrinos. Diese neue niederenergetische Modellklasse hat einige außergewöhnliche Konsequenzen für Kosmologie, Astrophysik, Gravitation, und Teilchenphänomenologie. Zum Beispiel zeigen wir, dass aufgrund eines späten kosmischen Phasenübergangs im Neutrinosektor die kosmologischen Grenzen für die Neutrinomassen verschwinden. Darüber hinaus untersuchen wir die Auswirkungen der vorhergesagten topologischen Defekte und der verstärkten kosmischen Neutrino-Selbstwechselwirkungen auf Dunkle Materie und Dunkle Strahlung im späten Universum. Im astrophysikalischen Bereich ist die wichtigste Modellvorhersage die Verstärkung von Neutrinozerfällen, welche in extraterrestrischen Neutrinoflüssen beobachtbar sind. In Bezug auf Gravitationsmessungen implizieren unsere Modelle verschiedene Polarisationsintensitäten von Gravitationswellen sowie eine neue kurzreichweitige Kraft zwischen Nukleonen, konkurrierend mit der Gravitationskraft. Im Hinblick auf Teilchenphänomenlogie erläutern wir mögliche Signaturen von flavor-verletzenden Prozessen, Licht-durch-die-Wand-Signalen, und etwaigen sterilen Neutrinos in Short-Baseline-Experimenten. Wir kommentieren, wie diese Modellvorhersagen mit laufenden und zukünftigen Experimenten getestet werden können, insbesondere mit Euclid, IceCube, KATRIN und PTOLEMY
Time-varying neutrino mass from a supercooled phase transition: current cosmological constraints and impact on the - plane
In this paper we investigate a time-varying neutrino mass model, motivated by
the mild tension between cosmic microwave background (CMB) measurements of the
matter fluctuations and those obtained from low-redshift data. We modify the
minimal case of the model proposed by Dvali and Funcke (2016) that predicts
late neutrino mass generation in a post-recombination cosmic phase transition,
by assuming that neutrino asymmetries allow for the presence of relic neutrinos
in the late-time Universe. We show that, if the transition is supercooled,
current cosmological data (including CMB temperature, polarization and lensing,
baryon acoustic oscillations, and Type Ia supernovae) prefer the scale factor
of the phase transition to be very large, peaking at , and
therefore supporting a cosmological scenario in which neutrinos are almost
massless until very recent times. We find that in this scenario the
cosmological bound on the total sum of the neutrino masses today is
significantly weakened compared to the standard case of constant-mass
neutrinos, with ~eV at 95\% confidence, and in agreement with
the model predictions. The main reason for this weaker bound is a large
correlation arising between the dark energy and neutrino components in the
presence of false vacuum energy that converts into the non-zero neutrino masses
after the transition. This result provides new targets for the coming KATRIN
and PTOLEMY experiments. We also show that the time-varying neutrino mass model
considered here does not provide a clear explanation to the existing
cosmological - discrepancies.Comment: 13 pages, 13 figures, matches updated version accepted by Physical
Review
Exploring the CP-Violating Dashen Phase in the Schwinger Model with Tensor Networks
We numerically study the phase structure of the two-flavor Schwinger model
with matrix product states, focusing on the (1+1)-dimensional analog of the
CP-violating Dashen phase in QCD. Simulating the model around the point where
the positive mass of one fermion flavor corresponds to the negative mass of the
other fermion flavor, we explore a regime afflicted by the sign problem for
conventional Monte Carlo techniques. Our results indicate that the model
undergoes a CP-violating Dashen phase transition at this point, which manifests
itself in abrupt changes of the average electric field and the analog of the
pion condensate in the model. Studying the scaling of the bipartite
entanglement entropy as a function of the volume, we find clear indications
that this transition is not of first order.Comment: 8 pages, 3 figure
Computing the Mass Shift of Wilson and Staggered Fermions in the Lattice Schwinger Model with Matrix Product States
Simulations of lattice gauge theories with tensor networks and quantum
computing have so far mainly focused on staggered fermions. In this paper, we
use matrix product states to study Wilson fermions in the Hamiltonian
formulation and present a novel method to determine the additive mass
renormalization. Focusing on the single-flavor Schwinger model as a benchmark
model, we investigate the regime of a nonvanishing topological -term,
which is inaccessible to conventional Monte Carlo methods. We systematically
explore the dependence of the mass shift on the volume, the lattice spacing,
the -parameter, and the Wilson parameter. This allows us to follow
lines of constant renormalized mass, and therefore to substantially improve the
continuum extrapolation of the mass gap and the electric field density. For
small values of the mass, our continuum results agree with the theoretical
prediction from mass perturbation theory. Going beyond Wilson fermions, our
technique can also be applied to staggered fermions, and we demonstrate that
the results of our approach agree with a recent theoretical prediction for the
mass shift at sufficiently large volumes.Comment: 12 pages, 11 figure
Mass Renormalization of the Schwinger Model with Wilson and Staggered Fermions in the Hamiltonian Lattice Formulation
Lattice computations in the Hamiltonian formulation have so far mainly
focused on staggered fermions. In these proceedings, we study Wilson fermions
in the Hamiltonian formulation and propose a new method to determine the
resulting mass shift. As a benchmark study, we examine the one-flavour
Schwinger model with Wilson fermions and a topological -term using
matrix product states. Wilson fermions explicitly break chiral symmetry; thus,
the bare mass of the lattice model receives an additive renormalization. In
order to measure this mass shift directly, we develop a method that is suitable
for the Hamiltonian formulation, which relies on the fact that the vacuum
expectation value of the electric field density vanishes when the renormalized
mass is zero. We examine the dependence of the mass shift on the lattice
spacing, the lattice volume, the -parameter, and the Wilson parameter.
Using the mass shift, we then perform the continuum extrapolation of the
electric field density and compare the resulting mass dependence to the
analytical predictions of mass perturbation theory. We demonstrate that
incorporating the mass shift significantly improves the continuum
extrapolation. Finally, we apply our method to the same model using staggered
fermions instead of Wilson fermions and compare the resulting mass shift to
recent theoretical predictions.Comment: 10 pages, Proceedings of the 39th International Symposium on Lattice
Field Theory, 8th-13th August 2022, Rheinische
Friedrich-Wilhelms-Universit\"at Bonn, German
Measurement Error Mitigation in Quantum Computers Through Classical Bit-Flip Correction
We develop a classical bit-flip correction method to mitigate measurement
errors on quantum computers. This method can be applied to any operator, any
number of qubits, and any realistic bit-flip probability. We first demonstrate
the successful performance of this method by correcting the noisy measurements
of the ground-state energy of the longitudinal Ising model. We then generalize
our results to arbitrary operators and test our method both numerically and
experimentally on IBM quantum hardware. As a result, our correction method
reduces the measurement error on the quantum hardware by up to one order of
magnitude. We finally discuss how to pre-process the method and extend it to
other errors sources beyond measurement errors. For local Hamiltonians, the
overhead costs are polynomial in the number of qubits, even if multi-qubit
correlations are included.Comment: 31 pages, 13 figure
Levels of Structural Integration Mediate the Impact of Metacognition on Functioning in Non-affective Psychosis: Adding a Psychodynamic Perspective to the Metacognitive Approach
Synthetic metacognition is defined by integrative and contextualizing processes of discrete reflexive moments. These processes are supposed to be needed to meet intrapsychic as well as interpersonal challenges and to meaningfully include psychotic experience in a personal life narrative. A substantial body of evidence has linked this phenomenon to psychosocial functioning and treatment options were developed. The concept of synthetic metacognition, measured with the Metacognition Assessment Scale-Abbreviated (MAS-A), rises hope to bridge gaps between therapeutic orientations and shares valuable parallels to modern psychodynamic constructs, especially the 'levels of structural integration' of the Operationalized Psychodynamic Diagnosis (OPD-2). As theoretical distinctions remain, aim of this study was to compare the predictive value of both constructs with regard to psychosocial functioning of patients with non-affective psychoses, measured with the International Classification of Functioning, Disability and Health (MINI-ICF-APP). It was further explored if levels of structural integration (OPD-LSIA) would mediate the impact of metacognition (MAS-A) on function (MINI-ICF-APP). Expert ratings of synthetic metacognition (MAS-A), the OPD-2 'levels of structural integration' axis (OPD-LSIA), psychosocial functioning (MINI-ICF-APP) and assessments of general cognition and symptoms were applied to 100 individuals with non-affective psychoses. Whereas both, MAS-A and OPD-LSIA, significantly predicted MINI-ICF-APP beyond cognition and symptoms, OPD-LSIA explained a higher share of variance and mediated the impact of MAS-A on MINI-ICF-APP. Levels of structural integration, including the quality of internalized object representations and unconscious interpersonal schemas, might therefore be considered as valuable predictors of social functioning and as one therapeutic focus in patients with non-affective psychoses. Structural integration might go beyond and form the base of a person's actual reflexive and metacognitive capabilities. Psychotherapeutic procedures specific for psychoses may promote and challenge a patient's metacognitive capacities, but should equally take the need for maturing structural skills into account. Modern psychodynamic approaches to psychosis are shortly presented, providing concepts and techniques for the implicit regulation of interpersonal experience and aiming at structural integration in this patient group
Quantum spin helices more stable than the ground state: onset of helical protection
Topological magnetic structures are promising candidates for resilient
information storage. An elementary example are spin helices in one-dimensional
easy-plane quantum magnets. To quantify their stability, we numerically
implement the stochastic Schr\"odinger equation and time-dependent perturbation
theory for spin chains with fluctuating local magnetic fields. We find two
classes of quantum spin helices that can reach and even exceed ground-state
stability: Spin-current-maximizing helices and, for fine-tuned boundary
conditions, the recently discovered "phantom helices". Beyond that, we show
that the helicity itself (left- or right-rotating) is even more stable. We
explain these findings by separated helical sectors and connect them to
topological sectors in continuous spin systems. The resulting helical
protection mechanism is a promising phenomenon towards stabilizing helical
quantum structures, e.g., in ultracold atoms and solid state systems. We also
identify an - up to our knowledge - previously unknown new type of phantom
helices.Comment: 6+4 pages, 3 figures; version 2: minor updates, additional reference
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