Anomalous optical absorption in a random system with scale-free disorder

We report on an anomalous behavior of the absorption spectrum in a one-dimensional lattice with long-range-correlated diagonal disorder with a power-like spectrum in the form S(k) ~ 1/k^A. These type of correlations give rise to a phase of extended states at the band center, provided A is larger than a critical value A_c. We show that for A < A_c the absorption spectrum is single-peaked, while an additional peak arises when A > A_c, signalling the occurrence of the Anderson transition. The peak is located slightly below the low-energy mobility edge, providing a unique spectroscopic tool to monitor the latter. We present qualitative arguments explaining this anomaly.Comment: 4 pages, 4 postscript figures, uses revtex

Spin excitations of weakly coupled magnetic atoms

A theoretical description of the measured differential conductance through magnetic atoms on a Cu2N/Cu(100) substrate is presented [Otte et al., Phys. Rev. Lett. 103, 107203 (2009)]. In particular, we analyze the case of a weakly coupled Co/ Fe dimer. The starting point of our model is an ionic Hamiltonian which describes the inelastic electron tunneling excitations and the Kondo resonances as due to atomic spin fluctuations associated with electron cotunneling processes in the tip-atom-surface system. The interaction terms of this Hamiltonian are written in the basis set of the eigenstates of the atomic part, which in the present case includes the crystalline and Zeeman fields and also, a Heisenberg exchange coupling between the two spins. The appropriate Green’s functions that define the differential conductance spectra are calculated by means of the equation-of-motion method.We obtain, in this form, a very satisfactory description of the overall experimental findings related to the behavior of the spin state excitations and Kondo resonance structures in the presence of an applied magnetic fieldE.C.G. acknowledges financial support by ANPCyT through Grant No. PICT-2010-0294, CONICET through Grant No. PIP-201101-00621, and U.N.L. through CAI+D grants. F.F. has been supported by the Spanish MICIIN under Contract No. FIS2010-1604

Renormalization of the baryon axial vector current in large-N_c chiral perturbation theory

The baryon axial vector current is computed at one-loop order in heavy baryon chiral perturbation theory in the large-N_c limit, where N_c is the number of colors. Loop graphs with octet and decuplet intermediate states cancel to various orders in N_c as a consequence of the large-N_c spin-flavor symmetry of QCD baryons. These cancellations are explicitly shown for the general case of N_f flavors of light quarks. In particular, a new generic cancellation is identified in the renormalization of the baryon axial vector current at one-loop order. A comparison with conventional heavy baryon chiral perturbation theory is performed at the physical values N_c=3, N_f=3.Comment: REVTex4, 29 pages, 2 figures, 6 tables. Equations (32) and (81) corrected. Some typos fixed. Results and conclusions remain unchange

Effective Lagrangian description of Higgs mediated flavor violating electromagnetic transitions: implications on lepton flavor violation

Higgs mediated flavor violating electromagnetic interactions, induced at the one--loop level by a nondiagonal $Hf_if_j$ vertex, with $f_i$ and $f_j$ charged leptons or quarks, are studied within the context of a completely general effective Yukawa sector that comprises $SU_L(2)\times U_Y(1)$--invariant operators of up to dimension--six. Exact formulae for the one--loop $\gamma f_if_j$ and $\gamma \gamma f_if_j$ couplings are presented and their related processes used to study the phenomena of Higgs mediated lepton flavor violation. The experimental limit on the $\mu \to e\gamma$ decay is used to derive a bound on the branching ratio of the $\mu \to e\gamma \gamma$ transition, which is 6 orders of magnitude stronger than the current experimental limit. Previous results on the $\tau \to \mu \gamma$ and $\tau \to \mu \gamma \gamma$ decays are reproduced. The possibility of detecting signals of lepton flavor violation at $\gamma \gamma$ colliders is explored through the $\gamma \gamma \to l_il_j$ reaction, putting special emphasis on the $\tau \mu$ final state. Using the bound imposed on the $H\tau \mu$ vertex by the current experimental data on the muon anomalous magnetic moment, it is found that about half a hundred events may be produced in the International Linear Collider.Comment: 18 pages, 12 figure

Galaxy disks do not need to survive in the L-CDM paradigm: the galaxy merger rate out to z~1.5 from morpho-kinematic data

About two-thirds of present-day, large galaxies are spirals such as the Milky Way or Andromeda, but the way their thin rotating disks formed remains uncertain. Observations have revealed that half of their progenitors, six billion years ago, had peculiar morphologies and/or kinematics, which exclude them from the Hubble sequence. Major mergers, i.e., fusions between galaxies of similar mass, are found to be the likeliest driver for such strong peculiarities. However, thin disks are fragile and easily destroyed by such violent collisions, which creates a critical tension between the observed fraction of thin disks and their survival within the L-CDM paradigm. Here we show that the observed high occurrence of mergers amongst their progenitors is only apparent and is resolved when using morpho-kinematic observations which are sensitive to all the phases of the merging process. This provides an original way of narrowing down observational estimates of the galaxy merger rate and leads to a perfect match with predictions by state-of-the-art L-CDM semi-empirical models with no particular fine-tuning needed. These results imply that half of local thin disks do not survive but are actually rebuilt after a gas-rich major merger occurring in the past nine billion years, i.e., two-thirds of the lifetime of the Universe. This emphasizes the need to study how thin disks can form in halos with a more active merger history than previously considered, and to investigate what is the origin of the gas reservoir from which local disks would reform.Comment: 19 pages, 7 figures, 2 tables. Accepted in ApJ. V2 to match proof corrections and added reference

High-precision analysis of binary stars with planets. I. Searching for condensation temperature trends in the HD 106515 system

We explore the probable chemical signature of planet formation in the remarkable binary system HD 106515. The A star hosts a massive long-period planet with 9 MJup detected by radial velocity. We also refine stellar and planetary parameters by using non-solar-scaled opacities when modeling the stars. Methods. We carried out a simultaneous determination of stellar parameters and abundances, by applying for the first time non-solar-scaled opacities in this binary system, in order to reach the highest possible precision. Results. The stars A and B in the binary system HD 106515 do not seem to be depleted in refractory elements, which is different when comparing the Sun with solar-twins. Then, the terrestrial planet formation would have been less efficient in the stars of this binary system. Together with HD 80606/7, this is the second binary system which does not seem to present a (terrestrial) signature of planet formation, and hosting both systems an eccentric giant planet. This is in agreement with numerical simulations, where the early dynamical evolution of eccentric giant planets clear out most of the possible terrestrial planets in the inner zone. We refined the stellar mass, radius and age for both stars and found a notable difference of 78% in R compared to previous works. We also refined the planet mass to mp sini = 9.08 +/- 0.20 MJup, which differs by 6% compared with literature. In addition, we showed that the non-solar-scaled solution is not compatible with the classical solar-scaled method, and some abundance differences are comparable to NLTE or GCE effects specially when using the Sun as reference. Then, we encourage the use of non-solar-scaled opacities in high-precision studies such as the detection of Tc trends.[abridged]Comment: 9 pages, 10 figures, A&A accepted. arXiv admin note: text overlap with arXiv:1507.0812

The Formation of Large Galactic Disks: Revival or Survival?

Using the deepest and the most complete set of observations of distant galaxies, we investigate how extended disks could have formed. Observations include spatially-resolved kinematics, detailed morphologies and photometry from UV to mid-IR. Six billion years ago, half of the present-day spiral progenitors had anomalous kinematics and morphologies, as well as relatively high gas fractions. We argue that gas-rich major mergers, i.e., fusions between gas-rich disk galaxies of similar mass, can be the likeliest driver for such strong peculiarities. This suggests a new channel of disk formation, e.g. many disks could be reformed after gas-rich mergers. This is found to be in perfect agreement with predictions from the state-of-the-art LCDM semi-empirical models: due to our sensitivity in detecting mergers at all phases, from pairs to relaxed post-mergers, we find a more accurate merger rate. The scenario can be finally confronted to properties of nearby galaxies, including M31 and galaxies showing ultra-faint, gigantic structures in their haloes.Comment: Proceedings of the annual meeting of the French Astronomical Society, 2011, 6 pages, 1 Figur