The acoustic cut-off frequency of the Sun and the solar magnetic activity cycle

The acoustic cut-off frequency -the highest frequency for acoustic solar eigenmodes- is an important parameter of the solar atmosphere as it determines the upper boundary of the p-mode resonant cavities. At frequencies beyond this value, acoustic disturbances are no longer trapped but traveling waves. Interference amongst them give rise to higher-frequency peaks -the pseudomodes- in the solar acoustic spectrum. The pseudomodes are shifted slightly in frequency with respect to p modes making possible the use of pseudomodes to determine the acoustic cut-off frequency. Using data from GOLF and VIRGO instruments on board the SOHO spacecraft, we calculate the acoustic cut-off frequency using the coherence function between both the velocity and intensity sets of data. By using data gathered by these instruments during the entire lifetime of the mission (1996 till the present), a variation in the acoustic cut-off frequency with the solar magnetic activity cycle is found.Comment: Paper accepted in ApJ. 26 Pages, 9 figure

Cosmic magnetic fields and dark energy in extended electromagnetism

We discuss an extended version of electromagnetism in which the usual gauge fixing term is promoted into a physical contribution that introduces a new scalar state in the theory. This new state can be generated from vacuum quantum fluctuations during an inflationary era and, on super-Hubble scales, gives rise to an effective cosmological constant. The value of such a cosmological constant coincides with the one inferred from observations as long as inflation took place at the electroweak scale. On the other hand, the new state also generates an effective electric charge density on sub-Hubble scales that produces both vorticity and magnetic fields with coherent lengths as large as the present Hubble horizon.Comment: 4 pages, 2 figures. Contribution to the proceedings of Spanish Relativity Meeting 2010, Granada, Spain, 6-10 September 201

CP4 miracle: shaping Yukawa sector with CP symmetry of order four

We explore the phenomenology of a unique three-Higgs-doublet model based on the single CP symmetry of order 4 (CP4) without any accidental symmetries. The CP4 symmetry is imposed on the scalar potential and Yukawa interactions, strongly shaping both sectors of the model and leading to a very characteristic phenomenology. The scalar sector is analyzed in detail, and in the Yukawa sector we list all possible CP4-symmetric structures which do not run into immediate conflict with experiment, namely, do not lead to massless or mass-degenerate quarks nor to insufficient mixing or CP-violation in the CKM matrix. We show that the parameter space of the model, although very constrained by CP4, is large enough to comply with the electroweak precision data and the LHC results for the 125 GeV Higgs boson phenomenology, as well as to perfectly reproduce all fermion masses, mixing, and CP violation. Despite the presence of flavor changing neutral currents mediated by heavy Higgs scalars, we find through a parameter space scan many points which accurately reproduce the kaon CP-violating parameter $\epsilon_K$ as well as oscillation parameters in K and $B_{(s)}$ mesons. Thus, CP4 offers a novel minimalistic framework for building models with very few assumptions, sufficient predictive power, and rich phenomenology yet to be explored.Comment: 39 pages, 8 figures, 1 table; v2: expanded discussion, extra references, matches published versio

How to automate a kinematic mount using a 3D printed Arduino-based system

We demonstrate a simple, flexible and cost-effective system to automatize most of the kinematic mounts available nowadays on the market. It combines 3D printed components, an Arduino board, stepper motors, and simple electronics. The system developed can control independently and simultaneously up to ten stepper motors using commands sent through the serial port, and it is suitable for applications where optical realignment using flat mirrors is required on a periodic basis.Comment: 9 pages, 8 figure

The onset of solar cycle 24: What global acoustic modes are telling us

We study the response of the low-degree, solar p-mode frequencies to the unusually extended minimum of solar surface activity since 2007. A total of 4768 days of observations collected by the space-based, Sun-as-a-star helioseismic GOLF instrument are analyzed. A multi-step iterative maximum-likelihood fitting method is applied to subseries of 365 days and 91.25 days to extract the p-mode parameters. Temporal variations of the l=0, 1, and 2 p-mode frequencies are then obtained from April 1996 to May 2009. While the p-mode frequency shifts are closely correlated with solar surface activity proxies during the past solar cycles, the frequency shifts of the l=0 and l=2 modes show an increase from the second half of 2007, when no significant surface activity is observable. On the other hand, the l=1 modes follow the general decreasing trend of the solar surface activity. The different behaviours between the l=0 and l=2 modes and the l=1 modes can be interpreted as different geometrical responses to the spatial distribution of the solar magnetic field beneath the surface of the Sun. The analysis of the low-degree, solar p-mode frequency shifts indicates that the solar activity cycle 24 started late 2007, despite the absence of activity on the solar surface.Comment: To be accepted by A&A (with minor revisions), 4 pages, 3 figures, 1 tabl

On the evolution of the molecular line profiles induced by the propagation of C-shock waves

We present the first results of the expected variations of the molecular line emission arising from material recently affected by C-shocks (shock precursors). Our parametric model of the structure of C-shocks has been coupled with a radiative transfer code to calculate the molecular excitation and line profiles of shock tracers such as SiO, and of ion and neutral molecules such as H13CO+ and HN13C, as the shock propagates through the unperturbed medium. Our results show that the SiO emission arising from the early stage of the magnetic precursor typically has very narrow line profiles slightly shifted in velocity with respect to the ambient cloud. This narrow emission is generated in the region where the bulk of the ion fluid has already slipped to larger velocities in the precursor as observed toward the young L1448-mm outflow. This strongly suggests that the detection of narrow SiO emission and of an ion enhancement in young shocks, is produced by the magnetic precursor of C-shocks. In addition, our model shows that the different velocity components observed toward this outflow can be explained by the coexistence of different shocks at different evolutionary stages, within the same beam of the single-dish observations.Comment: 7 pages, 4 figures, accepted for publication in Ap

Development of the Red Sequence in Galaxy Clusters

We investigate the origin of the color-magnitude relation (CMR) observed in cluster galaxies by using a combination of a cosmological N-body simulation of a cluster of galaxies and a semi-analytic model of galaxy formation. The departure of galaxies in the bright end of the CMR with respect to the trend defined by less luminous galaxies could be explained by the influence of minor mergers.Comment: Proceedings IAU Symposium No. 267, 2009. Co-Evolution of Central Black Holes and Galaxie

Optical sectioning in induced coherence tomography with frequency-entangled photons

We demonstrate a different scheme to perform optical sectioning of a sample based on the concept of induced coherence [Zou et al., Phys. Rev. Lett. 67, 318 (1991)]. This can be viewed as a different type of optical coherence tomography scheme where the varying reflectivity of the sample along the direction of propagation of an optical beam translates into changes of the degree of first-order coherence between two beams. As a practical advantage the scheme allows probing the sample with one wavelength and measuring photons with another wavelength. In a bio-imaging scenario, this would result in a deeper penetration into the sample because of probing with longer wavelengths, while still using the optimum wavelength for detection. The scheme proposed here could achieve submicron axial resolution by making use of nonlinear parametric sources with broad spectral bandwidth emission.Comment: Published version. 11 pages, 9 figure