Extended Quantum Dimer Model and novel valence-bond phases

We extend the quantum dimer model (QDM) introduced by Rokhsar and Kivelson so as to construct a concrete example of the model which exhibits the first-order phase transition between different valence-bond solids suggested recently by Batista and Trugman and look for the possibility of other exotic dimer states. We show that our model contains three exotic valence-bond phases (herringbone, checkerboard and dimer smectic) in the ground-state phase diagram and that it realizes the phase transition from the staggered valence-bond solid to the herringbone one. The checkerboard phase has four-fold rotational symmetry, while the dimer smectic, in the absence of quantum fluctuations, has massive degeneracy originating from partial ordering only in one of the two spatial directions. A resonance process involving three dimers resolves this massive degeneracy and dimer smectic gets ordered (order from disorder).Comment: 20 pages, 13 figures, accepted for publication in J. Stat. Mec

Avaliação de testes estatísticos em dados de Q-PCR.

A Q-PCR (Quantitative Polymerase Chain Reaction) é uma técnica que permite quantificar de forma precisa, especifica e indireta a quantidade de RNA mensageiro presente em uma determinada amostra. A Q-PCR apresenta vantagens metodológicas para a quantificação do RNA mensageiro quando comparada às técnicas de Northern Blot e Reverse Transcription Polymerase Chain Reaction, facilitando estudos de expressão gênica diferenciada. No entanto, experimentos de Q-PCR freqüentemente apresentam limitações amostrais (6= N =12) e são analisados por testes estatísticos tradicionais (paramétricos) sem a devida verificação da condição de normalidade da variável resposta e de homogeneidade das variâncias dos grupos experimentais, exigidas nesses testes. O presente trabalho avaliou quatro testes estatísticos de comparação de médias e/ou medianas, entre os grupos controle(C) e tratado (T), com objetivo de propor o teste mais adequado para estudar expressão gênica com dados de Q-PCR. O experimento foi realizado na Embrapa Pecuária Sudeste ? São Carlos, Brasil, utilizando 10 bezerros Nelore (Bos indicus), divididos aleatoriamente em dois grupos de cinco animais: grupo tratado (T) infestado artificialmente com carrapatos Rhipicephalus (Boophilus) microplus e grupo controle (C) livre de infestação. Os dados foram submetidos a quatro diferentes testes estatísticos, sendo o primeiro paramétrico (ANOVA com teste t) e os demais não-paramétricos (teste de mediana, boot strap, e Rest.). Quando o gene referência (gene de expressão constitutiva) apresentou pequena variação entre os tratamentos (0,6 = P = 1) os testes estatísticos, com exceção do teste de mediana, apresentaram valores de probabilidade confiáveis e semelhantes. Porém, quando o gene referência apresentou variação entre os tratamentos (P = 0,6) todos os testes apresentaram resultados distintos, e o teste Rest©, não-paramétrico, de comparações das médias e com ajustes para eficiência de amplificação do primer e valores de probabilidade do gene referência, foi o mais adequado para analisar dados de Q-PCR

Subaru Deep Survey VI. A Census of Lyman Break Galaxies at z=4 and 5 in the Subaru Deep Fields: Clustering Properties

We investigate the clustering properties of 2,600 Lyman Break Galaxies (LBGs) at z=3.5-5.2 in two large blank fields, the Subaru Deep Field and the Subaru/XMM Deep Field (600arcmin^2 each). The angular correlation functions of these LBGs show a clear clustering at both z~4 and 5. The correlation lengths are r_0= 4.1^{+0.2}_{-0.2} and 5.9^{+1.3}_{-1.7} h_{100}^{-1} Mpc (r_0= 5.1^{+1.0}_{-1.1} and 5.9^{+1.3}_{-1.7} h_{100}^{-1} Mpc) for all the detected LBGs (for L>L* LBGs) at z~4 and 5, respectively. These correlation lengths correspond to galaxy-dark matter biases of b_g= 2.9^{+0.1}_{-0.1} and 4.6^{+0.9}_{-1.2} (b_g=3.5^{+0.6}_{-0.7} and 4.6^{+0.9}_{-1.2}), for all the detected LBGs (for L>L^* LBGs) at z~4 and 5, respectively. These results, combined with estimates for z~3 LBGs in the literature, show that the correlation length of L>L^* LBGs is almost constant, ~5 h_{100}^{-1} Mpc, over z~3-5, while the bias monotonically increases with redshift at z>3. We also find that for LBGs at z~4 the clustering amplitude increases with UV-continuum luminosity and with the amount of dust extinction. We estimate the mass of dark halos hosting various kinds of high-z galaxies including LBGs with the analytic model given by Sheth & Tormen (1999). We find that the typical mass of dark halos hosting L>L^* LBGs is about 1x10^{12} h_{70}^{-1}Msol over z~3-5, which is comparable to that of the Milky Way Galaxy. A single dark halo with ~10^{12} h_{70}^{-1} Msol is found to host 0.1-0.3 LBG on average but host about four K-band selected galaxies.Comment: 33 pages, 12 figures, ApJ in press. Paper with high resolution figures is available at http://hikari.astron.s.u-tokyo.ac.jp/~ouchi/work/astroph/SDS_V_VI/SDS_VI.pdf (PDF) (The abstract was reduced by the revision.

Probing the evolution of early-type galaxies using multi-colour number counts and redshift distributions

We investigate pure luminosity evolution models for early-type (elliptical and S0) galaxies (i.e., no number density change or morphology transition), and examine whether these models are consistent with observed number counts in the B, I and K bands and redshift distributions of two samples of faint galaxies selected in the I and K bands. The models are characterized by the star formation time scale $\tau_{SF}$ and the time $t_{gw}$ when galactic wind blows in addition to several other conventional parameters. We find the single-burst model ($\tau_{SF}$=0.1 Gyr and $t_{gw}$=0.353 Gyr), which is known to reproduce the photometric properties of early-type galaxies in clusters, is inconsistent with redshift distributions of early-type galaxies in the field environment due to overpredictions of galaxies at z\gsim1.4 even with strong extinction which is at work until $t_{gw}$. In order for dust extinction to be more effective, we change $\tau_{SF}$ and $t_{gw}$ as free parameters, and find that models with \tau_{SF}\gsim0.5 Gyr and $t_{gw}>1.0$ Gyr can be made consistent with both the observed redshift distributions and number counts, if we introduce strong extinction $(E(B-V)\geq1$ as a peak value). These results suggest that early-type galaxies in the field environment do not have the same evolutionary history as described by the single-burst model.Comment: 6 pages including 4 PS figures; accepted for publication in MNRA

Early-type Galaxies at z ~ 1.3. II. Masses and Ages of Early-type Galaxies in Different Environments and Their Dependence on Stellar Population Model Assumptions

We have derived masses and ages for 79 early-type galaxies (ETGs) in different environments at z ~ 1.3 in the Lynx supercluster and in the GOODS/CDF-S field using multi-wavelength (0.6-4.5 μm; KPNO, Palomar, Keck, Hubble Space Telescope, Spitzer) data sets. At this redshift the contribution of the thermally pulsing asymptotic giant branch (TP-AGB) phase is important for ETGs, and the mass and age estimates depend on the choice of the stellar population model used in the spectral energy distribution fits. We describe in detail the differences among model predictions for a large range of galaxy ages, showing the dependence of these differences on age. Current models still yield large uncertainties. While recent models from Maraston and Charlot & Bruzual offer better modeling of the TP-AGB phase with respect to less recent Bruzual & Charlot models, their predictions do not often match. The modeling of this TP-AGB phase has a significant impact on the derived parameters for galaxies observed at high redshift. Some of our results do not depend on the choice of the model: for all models, the most massive galaxies are the oldest ones, independent of the environment. When using the Maraston and Charlot & Bruzual models, the mass distribution is similar in the clusters and in the groups, whereas in our field sample there is a deficit of massive (M ≳ 10^(11) M_☉) ETGs. According to those last models, ETGs belonging to the cluster environment host on average older stars with respect to group and field populations. This difference is less significant than the age difference in galaxies of different masses