Singlet-Assisted Electroweak Baryogenesis in Effective Field Theory and SO(6)/SO(5) Composite Higgs Models

It is known that the Baryon-Asymmetry in the Universe (BAU) can be generated in Electroweak Baryogenesis when minimally extending the Standard Model (SM) with a scalar singlet. A particularly well-researched class of models features a Z2 symmetry of the singlet that is spontaneously broken around the electroweak scale. However, such a scenario generically leads to phenomenologically problematic domain walls. Here, a thermal history in which the Z2 symmetry is not restored at high temperatures is envisioned, as accomplished by introducing D ≤ 6 operators in a general effective field theory (EFT). Introducing non-renormalizable operators is the logical consequence of understanding the theory as the low-energy tail of a more complete theory, such as in Composite Higgs (CH) scenarios, which can additionally address the hierarchy problem and the flavor hierarchy puzzle. Here I present a comprehensive analysis of the Yukawa terms and the scalar potential generated up to D = 6 terms in various SO(6)/SO(5) CH models. To this end, a Spurion Analysis with SM fermions embedded in the (1), 6, 15 or 20′ representations of SO(6) is performed. The most promising model is successfully matched to the general EFT, showing that it can generate the correct BAU

Z₂ Non-Restoration and Composite Higgs: Singlet-Assisted Baryogenesis w/o Topological Defects

Simple scalar-singlet extensions of the Standard Model with a (spontaneouslybroken) $Z_2$ symmetry allow for a strong first order electroweak phasetransition, as sought in order to realize electroweak baryogenesis. Howeverthey generically also lead to the emergence of phenomenologically problematicdomain walls. Here we present a framework with a real scalar singlet thatfeatures a different thermal history that avoids this problem by neverrestoring the $Z_2$ symmetry in the early universe. This is accomplished byconsidering $D>4$ operators that emerge on general grounds, understanding themodel as the low energy tail of a more complete theory, like for example incomposite Higgs scenarios. Sticking to the latter framework, we present aconcrete $SO(6)/SO(5)$ composite realization of the idea. To this end, weadditionally provide a complete classification of the structure of the Higgspotential (and the Yukawa couplings) in $SO(6)/SO(5)$ models with fermions inthe ${\bf 1, 6, 15}$ or ${\bf 20^\prime}$ of $SO(6)$.<br

Energetics and electronic structure of phenyl-disubstituted polyacetylene: A first-principles study

Phenyl-disubstituted polyacetylene (PDPA) is an organic semiconductor which has been studied during the last years for its efficient photo-luminescence. In contrast, the molecular geometry, providing the basis for the electronic and optical properties, has been hardly investigated. In this paper, we apply a density-functional-theory based molecular-dynamics approach to reveal the molecular structure of PDPA in detail. We find that oligomers of this material are limited in length, being stable only up to eight repeat units, while the polymer is energetically unfavorable. These facts, which are in excellent agreement with experimental findings, are explained through a detailed analysis of the bond lengths. A consequence of the latter is the appearance of pronounced torsion angles of the phenyl rings with respect to the plane of the polyene backbone, ranging from $55^{\circ}$ up to $95^{\circ}$. We point out that such large torsion angles do not destroy the conjugation of the $\pi$ electrons from the backbone to the side phenyl rings, as is evident from the electronic charge density.Comment: 9 pages, 7 figures, accepted for publication in Phys. Rev.

Spin fluctuations and superconductivity in noncentrosymmetric heavy fermion systems CeRhSi3_3 and CeIrSi3_3

We study the normal and the superconducting properties in noncentrosymmetric heavy fermion superconductors CeRhSi$_3$ and CeIrSi$_3$. For the normal state, we show that experimentally observed linear temperature dependence of the resistivity is understood through the antiferromagnetic spin fluctuations near the quantum critical point (QCP) in three dimensions. For the superconducting state, we derive a general formula to calculate the upper critical field $H_{c2}$, with which we can treat the Pauli and the orbital depairing effect on an equal footing. The strong coupling effect for general electronic structures is also taken into account. We show that the experimentally observed features in $H_{c2}\parallel \hat{z}$, the huge value up to 30(T), the downward curvatures, and the strong pressure dependence, are naturally understood as an interplay of the Rashba spin-orbit interaction due to the lack of inversion symmetry and the spin fluctuations near the QCP. The large anisotropy between $H_{c2}\parallel \hat{z}$ and $H_{c2}\perp \hat{z}$ is explained in terms of the spin-orbit interaction. Furthermore, a possible realization of the Fulde-Ferrell- Larkin-Ovchinnikov state for $H\perp \hat{z}$ is studied. We also examine effects of spin-flip scattering processes in the pairing interaction and those of the applied magnetic field on the spin fluctuations. We find that the above mentioned results are robust against these effects. The consistency of our results strongly supports the scenario that the superconductivity in CeRhSi$_3$ and CeIrSi$_3$ is mediated by the spin fluctuations near the QCP.Comment: 21pages, 13figures, to be published in Phys. Rev.

Theory of nonlinear optical properties of phenyl-substituted polyacetylenes

In this paper we present a theoretical study of the third-order nonlinear optical properties of poly(diphenyl)polyacetylene (PDPA) pertaining to the third-harmonic-generation (THG) process. We study the aforesaid process in PDPA's using both the independent electron Hueckel model, as well as correlated-electron Pariser-Parr-Pople (P-P-P) model. The P-P-P model based calculations were performed using various configuration interaction (CI) methods such as the the multi-reference-singles-doubles CI (MRSDCI), and the quadruples-CI (QCI) methods, and the both longitudinal and the transverse components of third-order susceptibilities were computed. The Hueckel model calculations were performed on oligo-PDPA's containing up to fifty repeat units, while correlated calculations were performed for oligomers containing up to ten unit cells. At all levels of theory, the material exhibits highly anisotropic nonlinear optical response, in keeping with its structural anisotropy. We argue that the aforesaid anisotropy can be divided over two natural energy scales: (a) the low-energy response is predominantly longitudinal and is qualitatively similar to that of polyenes, while (b) the high-energy response is mainly transverse, and is qualitatively similar to that of trans-stilbene.Comment: 13 pages, 7 figures (included), to appear in Physical Review B (April 15, 2004

Consequence of Hawking radiation from 2d dilaton black holes

We investigate the CGHS model through numerical calculation. The behavior of the mass function, which we introduced in our previous work as a ``local mass'', is examined. We found that the mass function takes negative values, which means that the amount of Hawking radiation becomes greater than the initial mass of the black hole as in the case of the RST model.Comment: 17pages, 5 figures (three of them are attached, the other 2 figures are available on request. Some mistakes including typographic errors have been correcte

A study on correlation effects in two dimensional topological insulators

We investigate correlation effects in two dimensional topological insulators (TI). In the first part, we discuss finite size effects for interacting systems of different sizes in a ribbon geometry. For large systems, there are two pairs of well separated massless modes on both edges. For these systems, we analyze the finite size effects using a standard bosonization approach. For small systems, where the edge states are massive Dirac fermions, we use the inhomogeneous dynamical mean field theory (DMFT) combined with iterative perturbation theory as an impurity solver to study interaction effects. We show that the finite size gap in the edge states is renormalized for weak interactions, which is consistent with a Fermi-liquid picture for small size TIs. In the second part, we investigate phase transitions in finite size TIs at zero temperature focusing on the effects of possible inter-edge Umklapp scattering for the edge states within the inhomogeneous DMFT using the numerical renormalization group. We show that correlation effects are effectively stronger near the edge sites because the coordination number is smaller than in the bulk. Therefore, the localization of the edge states around the edge sites, which is a fundamental property in TIs, is weakened for strong coupling strengths. However, we find no signs for "edge Mott insulating states" and the system stays in the topological insulating state, which is adiabatically connected to the non-interacting state, for all interaction strengths smaller than the critical value. Increasing the interaction further, a nearly homogeneous Mott insulating state is stabilized.Comment: 20 page

Research on pre-slaughter stress and meat quality: A review of challenges faced under practical conditions

Transportation and handling of animals are important components in meat production systems. Animals destined for slaughter are stressed by factors such as loading, transportation, restraint, handling, and novelty of the slaughter environment, adverse weather conditions, hunger, thirst and fatigue. When an animal is stressed in the pre-slaughter environment, there is a rapid release of enzymes, cortisols and catecholamines which may lead to depletion of glycogen, high meat ultimate pH (pHu) and dark cuts. Pre-slaughter stress also affects the physiology of the animal resulting in an increase in creatine kinase (CK) activity, glucose, lactate and other blood metabolites. Pre-slaughter stress and meat quality is a wide topic and some research have been done albeit was conducted under experimental and controlled conditions. In real life situations many variables are not controlled. Data collection in practical conditions is complex because it is difficult to accurately take some of the measurements; for example the onset of the release of the enzymes and hormones. Moreover, there are difficulties in taking measurements from slaughterhouses and butcheries. Challenges that researchers, marketers and consumers face under practical conditions either on-farm, research stations, transfer centres, slaughter plants, abattoirs or butcheries; with regard to pre-slaughter stress and meat quality may affect the quality of the final products developed under such conditions. This review therefore aims to give a detailed outline on pre-slaughter stress, meat science research and challenges under practical conditions