Search

We consider a mechanism that causes a decrease in the attenuation of high energy gamma-ray flux from gamma ray burst GRB 221009A. The mechanism is based on the existence of a heavy mN∼(0.1−1) MeV mostly sterile neutrino N which mixes with active neutrinos. N’s are produced in the gamma-ray burst (GRB) in π and K decays via mixing with νμ. They undergo the radiative decay N→νγ on the way to Earth. The usual exponential attenuation of gamma rays is lifted to an attenuation inverse in the optical depth. Various restrictions on this scenario are discussed. We find that the high energy γ events at 18 TeV can be explained if (i) the GRB active neutrino fluence is close to the observed limit, (ii) the branching ratio of N→νγ is at least of the order 10%.

We show that vector-like quarks in the fundamental or higher-dimensional representations of QCD can generate the electro-weak scale in a phenomenologically viable way by chiral symmetry breaking condensates. The thereby generated scales are determined by numerically solving the Dyson-Schwinger equation and these scales are sizable, because they grow with the hard vector-like mass. Communicating such a scale to the Standard Model via a conformally invariant scalar sector can dynamically generate the electro-weak scale without a naturalness problem, because all non-dynamical mass scales are protected by chiral symmetry. We present a minimal setup which requires only a new neutral scalar with mass not too far above the electro-weak scale, as well as vector-like quarks at the (multi-)TeV scale. Both are consistent with current bounds and are attractive for future experimental searches at the LHC and future colliders. Depending on the hypercharge of the vector-like quarks, hadrons made of them are color-neutral bound states which would be interesting Dark Matter candidates., 19 pages, 9 figures, 1 table

The framework of compactified heterotic string theory offers consistent ultraviolet (UV) completions of the Standard Model (SM) of particle physics. In this approach, the existence of flavor symmetries beyond the SM is imperative and the flavor symmetries can be derived from the top down. Such a derivation uncovers a unified origin of traditional discrete flavor symmetries, discrete modular flavor symmetries, discrete R symmetries of supersymmetry, as well as charge-parity (CP) symmetry - altogether dubbed the eclectic flavor symmetry. I will illustrate how the eclectic flavor symmetry is unambiguously computed from the top-down construction, discuss the different arising sources of spontaneous flavor symmetry breaking, and expose possible lessons for bottom-up flavor model building. Finally, I will focus on one explicit example model that provides a successful fit to all available experimental data while giving rise to concrete predictions for so-far undetermined parameters., 14 pages+references, 5 figures, 6 tables; Contribution to the Proceedings of the 8th Symposium on Prospects in the Physics of Discrete Symmetries (DISCRETE 2022), 7-11 November 2022, Baden-Baden, Germany; extended version of: arXiv:2204.06581

We investigate charge-parity (CP) and non-CP outer automorphism of groups and the transformation behavior of group representations under them. We identify situations where composite and elementary states that transform in exactly the same representation of the group, transform differently under outer automorphisms. This can be instrumental in discriminating composite from elementary states solely by their quantum numbers with respect to the outer automorphism, i.e. without the need for explicit short distance scattering experiments. We discuss under what conditions such a distinction is unequivocally possible. We cleanly separate the case of symmetry constrained (representation) spaces from the case of multiple copies of identical representations in flavor space, and identify conditions under which non-trivial transformation in flavor space can be enforced for composite states. Next to composite product states, we also discuss composite states in non-product representations. Comprehensive examples are given based on the finite groups $\Sigma(72)$ and $D_8$. The discussion also applies to $\mathrm{SU}(N)$ and we scrutinize recent claims in the literature that $\mathrm{SU}(2N)$ outer automorphism with antisymmetric matrices correspond to distinct outer automorphisms. We show that outer automorphism transformations with antisymmetric matrices are related by an inner automorphism to the standard $\mathbb{Z}_2$ outer automorphism of $\mathrm{SU}(N)$. As a direct implication, no non-trivial transformation behavior can arise for composite product states under the outer automorphism of $\mathrm{SU}(N)$., Comment: 29+10 pages, 1 table. Incl. rebuttal of claims of existence of non-standard outer automorphism transformation of $\mathrm{SU}(2N)$, as recently proposed by 1903.06662, 2111.04728, 2212.02413

We consider a mechanism which allows to decrease attenuation of high energy gamma ray flux from gamma ray burst GRB 221009A. The mechanism is based on the existence of a heavy $m_N\sim0.1\,\mathrm{MeV}$ mostly sterile neutrino $N$ which mixes with active neutrinos. $N$'s are produced in GRB in $\pi$ and $K$ decays via mixing with $\nu_\mu$. They undergo the radiative decay $N\rightarrow \nu \gamma$ on the way to the Earth. The usual exponential attenuation of gamma rays is lifted to an attenuation inverse in the optical depth. Various restrictions on this scenario are discussed. We find that the high energy $\gamma$ events at $18\,\mathrm{TeV}$ and potentially $251\,\mathrm{TeV}$ can be explained if (i) the GRB active neutrino fluence is close to the observed limit, (ii) the branching ratio of $N\rightarrow \nu \gamma$ is at least of the order 10%., Comment: 6 pages, 1 figure; v2: typos fixed, references added

The incorporation of Wilson lines leads to an extension of the modular symmetries of string compactification beyond SL(2,Z). In the simplest case with one Wilson line Z, Kähler modulus T and complex structure modulus U, we are led to the Siegel modular group Sp(4,Z). It includes SL(2,Z)T×SL(2,Z)U as well as Z2 mirror symmetry, which interchanges T and U. Possible applications to flavor physics of the Standard Model require the study of orbifolds of Sp(4,Z) to obtain chiral fermions. We identify the 13 possible orbifolds and determine their modular flavor symmetries as subgroups of Sp(4,Z). Some cases correspond to symmetric orbifolds that extend previously discussed cases of SL(2,Z). Others are based on asymmetric orbifold twists (including mirror symmetry) that do no longer allow for a simple intuitive geometrical interpretation and require further study. Sometimes they can be mapped back to symmetric orbifolds with quantized Wilson lines. The symmetries of Sp(4,Z) reveal exciting new aspects of modular symmetries with promising applications to flavor model building.

Flavor symmetry plays a crucial role in the standard model of particle physics but its origin is still unknown. We develop a new method (based on outer automorphisms of the Narain space group) to determine flavor symmetries within compactified string theory. A picture emerges where traditional (discrete) flavor symmetries, CP-like symmetries and modular symmetries (like T-duality) of string theory combine to unified flavor symmetries. The groups depend on the geometry of compact space and the geographical location of fields in the extra dimensions. We observe a phenomenon of "local flavor groups" with potentially different flavor symmetries for the various sectors of quarks and leptons. This should allow interesting connections to existing bottom-up attempts in flavor model building., Comment: 18 pages, 3 figures; v2: minor changes, version accepted by PLB

The incorporation of Wilson lines leads to an extension of the modular symmetries of string compactification beyond $\mathrm{SL}(2,\mathbb Z)$. In the simplest case with one Wilson line $Z$, K\"ahler modulus $T$ and complex structure modulus $U$, we are led to the Siegel modular group $\mathrm{Sp}(4,\mathbb Z)$. It includes $\mathrm{SL}(2,\mathbb Z)_T\times\mathrm{SL}(2,\mathbb Z)_U$ as well as $\mathbb Z_2$ mirror symmetry, which interchanges $T$ and $U$. Possible applications to flavor physics of the Standard Model require the study of orbifolds of $\mathrm{Sp}(4,\mathbb Z)$ to obtain chiral fermions. We identify the 13 possible orbifolds and determine their modular flavor symmetries as subgroups of $\mathrm{Sp}(4,\mathbb Z)$. Some cases correspond to symmetric orbifolds that extend previously discussed cases of $\mathrm{SL}(2,\mathbb Z)$. Others are based on asymmetric orbifold twists (including mirror symmetry) that do no longer allow for a simple intuitive geometrical interpretation and require further study. Sometimes they can be mapped back to symmetric orbifolds with quantized Wilson lines. The symmetries of $\mathrm{Sp}(4,\mathbb Z)$ reveal exciting new aspects of modular symmetries with promising applications to flavor model building., Comment: 27 pages + appendices, 2 tables

We present an in-depth analysis of a recently proposed Standard Model extension with a complete fourth generation of quarks and leptons, which are vectorlike with respect to the Standard Model gauge group and charged under a new spontaneously broken vectorlike U(1)′ gauge symmetry. The model is designed to explain the known muon anomalies, i.e., the observed deviations from Standard Model predictions in the anomalous magnetic moment of the muon, Δaμ, and in b→sℓ+ℓ− processes. We perform a global χ2 analysis of the data with 65 model parameters and including 98 observables. We find many points with χ2 per degree of freedom ≤1. The vectorlike leptons and the new heavy Z′ are typically much lighter than a TeV and would, thus, be eminently visible at the HL-LHC.

In this paper we present an in-depth analysis of a recently proposed Standard Model extension with a complete fourth generation of quarks and leptons, which are vector-like with respect to the Standard Model gauge group and charged under a new spontaneously broken vector-like $\mathrm{U(1)^\prime}$ gauge symmetry. The model is designed to explain the known muon anomalies, i.e. the observed deviations from Standard Model predictions in the anomalous magnetic moment of the muon, $\Delta a_\mu$, and in $b \rightarrow s \ell^+ \ell^-$ processes. We perform a global $\chi^2$ analysis of the data with $65$ model parameters and including $98$ observables. We find many points with $\chi^2$ per degree of freedom $\leq 1$. The vector-like leptons and the new heavy $Z^\prime$ are typically much lighter than a TeV and would, thus, be eminently visible at the HL-LHC., Comment: 80 pages, 9 figures and 21 tables

Modular transformations of string theory (including the well-known stringy dualities) play a crucial role in the discussion of discrete flavor symmetries in the Standard Model. They are at the origin of CP-transformations and provide a unification of CP with traditional flavor symmetries. Here, we present a novel, fully systematic method to reliably compute the unified flavor symmetry of the low-energy effective theory, including enhancements from the modular transformations of string theory. The unified flavor group is non-universal in moduli space and exhibits the phenomenon of “Local Flavor Unification” where different sectors of the theory can be subject to different flavor structures.

Flavor symmetry plays a crucial role in the standard model of particle physics but its origin is still unknown. We develop a new method (based on outer automorphisms of the Narain space group) to determine flavor symmetries within compactified string theory. A picture emerges where traditional (discrete) flavor symmetries, CP -like symmetries and modular symmetries (like T-duality) of string theory combine to unified flavor symmetries. The groups depend on the geometry of compact space and the geographical location of fields in the extra dimensions. We observe a phenomenon of “local flavor groups” with potentially different flavor symmetries for the various sectors of quarks and leptons. This should allow interesting connections to existing bottom-up attempts in flavor model building.

We consider the Standard Model (SM) with the addition of a $\mathrm{U(1)^\prime}$ gauge symmetry and a complete fourth family of quarks and leptons which are vector-like with respect to the full $\mathrm{SU(3)_C}\times \mathrm{SU(2)_L} \times \mathrm{U(1)_Y}\times \mathrm{U(1)^\prime}$ gauge symmetry. The model provides a unified explanation of experimental anomalies in $(g - 2)_\mu$ as well as $b \rightarrow s \ell^+ \ell^-$ decays. We find good fits to the deviations from the SM, while at the same time fitting all other SM observables. The model includes a new $Z^\prime$ gauge boson, a $\mathrm{U(1)^\prime}$-breaking scalar, and vector-like leptons all with mass of order a few $100$ GeV. It is consistent with all currently released high energy experimental data, however, it appears imminently testable with well designed future searches. Also precision flavor experiments, especially more accurate direct determinations of CKM matrix elements, would allow to probe the best fit points., Comment: 40 pages, 2 figures and 14 tables; Figure 2 replaced, references added

We identify a natural way to embed CP symmetry and its violation in string theory. The CP symmetry of the low energy effective theory is broken by the presence of heavy string modes. CP violation is the result of an interplay of CP and flavor symmetry. CP violating decays of the heavy modes could originate a cosmological matter-antimatter asymmetry.

We identify a natural way to embed $\mathcal{CP}$ symmetry and its violation in string theory. The $\mathcal{CP}$ symmetry of the low energy effective theory is broken by the presence of heavy string modes. $\mathcal{CP}$ violation is the result of an interplay of $\mathcal{CP}$ and flavor symmetry. $\mathcal{CP}$ violating decays of the heavy modes could originate a cosmological matter-antimatter asymmetry., Comment: 7 pages, 4 figures

Three-Higgs-doublet models (3HDM) allow for a novel, physically distinct form of CP invariance: CP symmetry of order 4 (CP4). Due to the large basis change freedom in 3HDM, it is imperative to recognize the presence of a possibly hidden CP4 in a basis-invariant way. In the present work, we solve this problem and establish basis-invariant necessary and sufficient conditions for a 3HDM to possess a CP4 symmetry. We also derive a basis-invariant criterion to decide whether or not a CP4 symmetric 3HDM possesses any additional CP symmetry, as well as a criterion to decide whether or not CP4 is spontaneously broken., Comment: 32 pages

A $\mathcal{CP}$ conserving $\mathrm{SU}(3)$ gauge theory is spontaneously broken to $\mathrm{T}_7$ by the vacuum expectation value (VEV) of a $\boldsymbol{15}$-plet. Even though the $\mathrm{SU}(3)$-$\,\mathcal{CP}$ transformation is not broken by the VEV, the theory exhibits physical $\mathcal{CP}$ violation in the broken phase. This is because the $\mathrm{SU}(3)$-$\,\mathcal{CP}$ transformation corresponds to the unique order-two outer automorphism of $\mathrm{T}_7$, which is not a physical $\mathcal{CP}$ transformation for the $\mathrm{T}_7$ states, and there is no other possible $\mathcal{CP}$ transformation. We explicitly demonstrate that $\mathcal{CP}$ is violated by calculating a $\mathcal{CP}$ odd decay asymmetry in the broken phase. This scenario provides us with a natural protection for topological vacuum terms, ensuring that $\theta\,G_{\mu\nu}\widetilde{G}^{\mu\nu}$ is absent even though $\mathcal{CP}$ is violated for the physical states of the model., Comment: 19 pages, 2 figures, 2 tables; v2: considering a different contribution to the decay asymmetry, conclusion unchanged

Outer automorphisms of symmetries (``symmetries of symmetries'') in relativistic quantum field theories are studied, including charge conjugation (C), space-reflection (P) , and time-reversal (T) transformations. It is shown that certain discrete groups can predict parameter independent CP violating complex phases with fixed geometrical values. The study of outer automorphisms which are not related to C, P, or T is pioneered. It is shown how outer automorphisms, in general, relate symmetry invariants and imply relations between distinct vacuum expectation values. Thereby, outer automorphisms can give rise to emergent symmetries. This underlies the prediction of spontaneous geometrical CP violation in a three Higgs doublet model. The possible relevance of outer automorphisms for a wide field of future studies is highlighted. Es werden äußere Automorphismen von Symmetrien (``Symmetrien von Symmetrien'') in relativistischen Quantenfeldtheorien untersucht, einschliesslich der Ladungskonjugation (C), Raumspiegelung (P), sowie der Zeitumkehrtransformation (T). Es wird gezeigt, dass gewisse diskrete Gruppen parameterunabhängige CP verletzende komplexe Phasen mit fixen geometrischen Werten vorhersagen können. Weiterhin werden erstmals äußere Automorphismen untersucht, die nichts mit C, P oder T zu tun haben. Im Allgemeinen implizieren äußere Automorphismen Relationen zwischen Symmetrieinvarianten und setzen unterschiedliche Vakuumerwartungswerte in Verbindung. Dadurch können äußere Automorphismen der Ursprung emergenter Symmetrien sein. Hierauf basiert die Vorhersage von spontaner CP Verletzung durch parameterunabhängige komplexe Phasen in einem Drei-Higgs-Modell. Die mögliche Relevanz von äußeren Automorphismen für viele weitere Anwendungsbereiche wird hervorgehoben.

Outer automorphisms of symmetries ("symmetries of symmetries") in relativistic quantum field theories are studied, including charge conjugation (C), space-reflection (P) , and time-reversal (T) transformations. The group theory of outer automorphisms is pedagogically introduced and it is shown that CP transformations are special outer automorphisms of the global, local, and space-time symmetries of a theory. It is shown that certain discrete groups allow for a group theoretical prediction of parameter independent CP violating complex phases with fixed geometrical values. The remainder of this thesis pioneers the study of outer automorphisms which are not related to C, P, or T. It is shown how outer automorphisms, in general, relate symmetry invariants and, in theories with spontaneous symmetry breaking, imply relations between different vacuum expectation values. Thereby, outer automorphisms can give rise to emergent symmetries. An example model with a discrete symmetry and three copies of the Standard Model Higgs field is discussed, in which the rich outer automorphism structure completely fixes the Higgs VEVs in their field space direction, including CP violating relative phases. This underlies the phenomenon of spontaneous geometrical CP violation. The possible relevance of outer automorphisms for a wide field of future studies is highlighted., Comment: PhD thesis, 130 pages, http://mediatum.ub.tum.de?id=1307248

We show that there is a class of finite groups, the so-called perfect groups, which cannot exhibit anomalies. This implies that all non-Abelian finite simple groups are anomaly-free. On the other hand, non-perfect groups generically suffer from anomalies. We present two different ways that allow one to understand these statements., 11 pages

This thesis summarizes and discusses results of subsoil stress, strain and strength measurements during field traffic with several load intensities on five sites in Sweden during the growing season. Vertical subsoil stress and displacement were measured by installing sensors horizontally 1 m into the soil at 0.3, 0.5 and 0.7 m depth through holes drilled from a pit whereby the soil flanking the sensors was left undisturbed. The soil precompression stress was determined on each occasion by sequential loading of soil samples in the laboratory. The topsoil properties had a large impact on the vertical subsoil stress, and the concentration of stress below a loaded surface appears to be affected by topsoil characteristics quite different than normally anticipated. The stress was clearly transmitted more directly and undiminished in relatively dry soil than in relatively wet soil. The precompression stress as determined by classical, uniaxial compression tests was a poor measure of soil ability to sustain non-recoverable deformation. The study showed that plastic deformation occurred at stress levels far below that predicted by the precompression stress. A linear correlation between elastic (recoverable) and plastic (non-recoverable) soil deformation indicates that soil should be regarded as an assemblage of soil elements with a stochastic distribution of the strength of the contact points. The practical implication of the observed soil behaviour is that the subsoil appears to be vulnerable to plastic (non-recoverable) deformation at lower wheel loads than normally anticipated. Furthermore, it is important that the stress in the contact area is as evenly distributed as possible to avoid unnecessarily high peak stresses. This calls for relatively fast and reliable methods that enable the land-users to optimise the stress distribution below tyres or tracks for specific soil types, water content and field operation. Furthermore, the results suggests an urgent need for engineering developments in vehicles with small load intensities.