The Resonance Peak in Sr2_2RuO4_4: Signature of Spin Triplet Pairing

We study the dynamical spin susceptibility, $\chi({\bf q}, \omega)$, in the normal and superconducting state of Sr$_2$RuO$_4$. In the normal state, we find a peak in the vicinity of ${\bf Q}_i\simeq (0.72\pi,0.72\pi)$ in agreement with recent inelastic neutron scattering (INS) experiments. We predict that for spin triplet pairing in the superconducting state a {\it resonance peak} appears in the out-of-plane component of $\chi$, but is absent in the in-plane component. In contrast, no resonance peak is expected for spin singlet pairing.Comment: 4 pages, 4 figures, final versio

Corporate Directors\u27 and Officers\u27 Cybersecurity Standard of Care: The Yahoo Data Breach

On September 22, 2016, Yahoo! Inc. ( Yahoo ) announced that a data breach and theft of information from over 500 million user accounts had taken place during 2014, marking the largest data breach ever at the time. The information stolen likely included names, birthdays, telephone numbers, email addresses, hashed passwords, and, in some cases, encrypted or unencrypted security questions and answers. Yahoo further disclosed its belief that the stolen data did not include unprotected passwords, payment card data, or bank account information. Just two months before Yahoo disclosed its 2014 data breach, it announced a proposed sale of the company\u27s core business to Verizon Communications. Then, during mid-December 2016, Yahoo announced that another 1 billion customer accounts had been compromised during 2013, a new record for largest data breach. Social media and electronic commerce websites face significant risk factors, and an acquirer may inherit cyber liability and vulnerabilities. The fact pattern in this announced acquisition raises a number of important corporate governance issues: whether Yahoo\u27s conduct leading up to the data breaches and its subsequent conduct constituted a breach of the duty to shareholders to provide security, the duty to monitor, the duty to disclose, or some combination thereof the impact on Verizon shareholders of the acquisition price renegotiation and Verizon\u27s assumption of post-closing cyber liabilities; and whether more drastic compensation clawbacks for key Yahoo executives would be appropriate. Cybersecurity remains a threat to all enterprises, and this Article contributes to the corporate governance literature, particularly as it applies to mergers and acquisitions and the management of cyber liability risk

Landscapes of luxury in the rural US depend on the recruitment of low-wage and often undocumented Latino workers

The last two decades have witnessed a dramatic growth in low-wage Latino and Latina immigrants, both documented and undocumented, finding employment and settling permanently in the United States. This process represents a key example of how globalization is transforming the U.S. economy and society. Of particular interest to scholars has been the diversification of Latino immigrant destinations, as a growing number of communities with no recent history of immigrant presence have witnessed rapid growth in immigrant residents. In new research, Lise Nelson, Laurie Trautman, and Peter B. Nelson argue that rural gentrification represents an important but overlooked ‘pull factor’ in the expansion of new Latino immigrant destinations in the rural United States. Their research reveals the process through which employers’ recruited workers to these geographically isolated locales, and how the gentrification boom witnessed in these places is supported by highly flexible immigrant labor regimes

Dirac Operators on Coset Spaces

The Dirac operator for a manifold Q, and its chirality operator when Q is even dimensional, have a central role in noncommutative geometry. We systematically develop the theory of this operator when Q=G/H, where G and H are compact connected Lie groups and G is simple. An elementary discussion of the differential geometric and bundle theoretic aspects of G/H, including its projective modules and complex, Kaehler and Riemannian structures, is presented for this purpose. An attractive feature of our approach is that it transparently shows obstructions to spin- and spin_c-structures. When a manifold is spin_c and not spin, U(1) gauge fields have to be introduced in a particular way to define spinors. Likewise, for manifolds like SU(3)/SO(3), which are not even spin_c, we show that SU(2) and higher rank gauge fields have to be introduced to define spinors. This result has potential consequences for string theories if such manifolds occur as D-branes. The spectra and eigenstates of the Dirac operator on spheres S^n=SO(n+1)/SO(n), invariant under SO(n+1), are explicitly found. Aspects of our work overlap with the earlier research of Cahen et al..Comment: section on Riemannian structure improved, references adde

Linear connections with propagating spin-3 field in gravity

We show that Fronsdal's Lagrangian for a free massless spin-3 gauge field in Minkowski spacetime is contained in a general Yang--Mills-like Lagrangian of metric-affine gravity (MAG), the gauge theory of the general affine group in the presence of a metric. Due to the geometric character of MAG, this can best be seen by using Vasiliev's frame formalism for higher-spin gauge fields in which the spin-3 frame is identified with the tracefree nonmetricity one-form associated with the shear generators of GL(n,R). Furthermore, for specific gravitational gauge models in the framework of full nonlinear MAG, exact solutions are constructed, featuring propagating massless and massive spin-3 fields.Comment: References added. Minor corrections and clarifications. To be published in Phys. Rev.

Big bounce from spin and torsion

The Einstein-Cartan-Sciama-Kibble theory of gravity naturally extends general relativity to account for the intrinsic spin of matter. Spacetime torsion, generated by spin of Dirac fields, induces gravitational repulsion in fermionic matter at extremely high densities and prevents the formation of singularities. Accordingly, the big bang is replaced by a bounce that occurred when the energy density $\epsilon\propto gT^4$ was on the order of $n^2/m_\textrm{Pl}^2$ (in natural units), where $n\propto gT^3$ is the fermion number density and $g$ is the number of thermal degrees of freedom. If the early Universe contained only the known standard-model particles ($g\approx 100$), then the energy density at the big bounce was about 15 times larger than the Planck energy. The minimum scale factor of the Universe (at the bounce) was about $10^{32}$ times smaller than its present value, giving \approx 50 \mum. If more fermions existed in the early Universe, then the spin-torsion coupling causes a bounce at a lower energy and larger scale factor. Recent observations of high-energy photons from gamma-ray bursts indicate that spacetime may behave classically even at scales below the Planck length, supporting the classical spin-torsion mechanism of the big bounce. Such a classical bounce prevents the matter in the contracting Universe from reaching the conditions at which a quantum bounce could possibly occur.Comment: 6 pages; published versio

Poincare gauge theory of gravity: Friedman cosmology with even and odd parity modes. Analytic part

We propose a cosmological model in the framework of the Poincar\'e gauge theory of gravity (PG). The gravitational Lagrangian is quadratic in curvature and torsion. In our specific model, the Lagrangian contains (i) the curvature scalar $R$ and the curvature pseudo-scalar $X$ linearly and quadratically (including an $RX$ term) and (ii) pieces quadratic in the torsion {\it vector} $\cal V$ and the torsion {\it axial} vector $\cal A$ (including a ${\cal V}{\cal A}$ term). We show generally that in quadratic PG models we have nearly the same number of parity conserving terms (`world') and of parity violating terms (`shadow world'). This offers new perspectives in cosmology for the coupling of gravity to matter and antimatter. Our specific model generalizes the fairly realistic `torsion cosmologies' of Shie-Nester-Yo (2008) and Chen et al.\ (2009). With a Friedman type ansatz for an orthonormal coframe and a Lorentz connection, we derive the two field equations of PG in an explicit form and discuss their general structure in detail. In particular, the second field equation can be reduced to first order ordinary differential equations for the curvature pieces $R(t)$ and $X(t)$. Including these along with certain relations obtained from the first field equation and curvature definitions, we present a first order system of equations suitable for numerical evaluation. This is deferred to the second, numerical part of this paper.Comment: Latex computerscript, 25 pages; mistakes corrected, references added, notation and title slightly changed; accepted by Phys. Rev.

Gravitational field around a screwed superconducting cosmic string in scalar-tensor theories

We obtain the solution that corresponds to a screwed superconducting cosmic string (SSCS) in the framework of a general scalar-tensor theory including torsion. We investigate the metric of the SSCS in Brans-Dicke theory with torsion and analyze the case without torsion. We show that in the case with torsion the space-time background presents other properties different from that in which torsion is absent. When the spin vanish, this torsion is a $\phi$-gradient and then it propagates outside of the string. We investigate the effect of torsion on the gravitational force and on the geodesics of a test-particle moving around the SSCS. The accretion of matter by wakes formation when a SSCS moves with speed $v$ is investigated. We compare our results with those obtained for cosmic strings in the framework of scalar-tensor theory.Comment: 22 pages, LaTeX, presented at the "XXII - Encontro Nacional de Fisica de Particulas e Campos", Sao Lourenco, MG, Brazi

The unexpected resurgence of Weyl geometry in late 20-th century physics

Weyl's original scale geometry of 1918 ("purely infinitesimal geometry") was withdrawn by its author from physical theorizing in the early 1920s. It had a comeback in the last third of the 20th century in different contexts: scalar tensor theories of gravity, foundations of gravity, foundations of quantum mechanics, elementary particle physics, and cosmology. It seems that Weyl geometry continues to offer an open research potential for the foundations of physics even after the turn to the new millennium.Comment: Completely rewritten conference paper 'Beyond Einstein', Mainz Sep 2008. Preprint ELHC (Epistemology of the LHC) 2017-02, 92 pages, 1 figur

Gravitational field around a time-like current-carrying screwed cosmic string in scalar-tensor theories

In this paper we obtain the space-time generated by a time-like current-carrying superconducting screwed cosmic string(TCSCS). This gravitational field is obtained in a modified scalar-tensor theory in the sense that torsion is taken into account. We show that this solution is comptible with a torsion field generated by the scalar field $\phi$. The analysis of gravitational effects of a TCSCS shows up that the torsion effects that appear in the physical frame of Jordan-Fierz can be described in a geometric form given by contorsion term plus a symmetric part which contains the scalar gradient. As an important application of this solution, we consider the linear perturbation method developed by Zel'dovich, investigate the accretion of cold dark matter due to the formation of wakes when a TCSCS moves with speed $v$ and discuss the role played by torsion. Our results are compared with those obtained for cosmic strings in the framework of scalar-tensor theories without taking torsion into account.Comment: 21 pages, no figures, Revised Version, presented at the "XXIV- Encontro Nacional de Fisica de Particulas e Campos ", Caxambu, MG, Brazil, to appear in Phys. Rev.