The NANOGrav 15 yr Data Set: Search for Transverse Polarization Modes in the Gravitational-wave Background

\ua9 2024. The Author(s). Published by the American Astronomical Society.Recently we found compelling evidence for a gravitational-wave background with Hellings and Downs (HD) correlations in our 15 yr data set. These correlations describe gravitational waves as predicted by general relativity, which has two transverse polarization modes. However, more general metric theories of gravity can have additional polarization modes, which produce different interpulsar correlations. In this work, we search the NANOGrav 15 yr data set for evidence of a gravitational-wave background with quadrupolar HD and scalar-transverse (ST) correlations. We find that HD correlations are the best fit to the data and no significant evidence in favor of ST correlations. While Bayes factors show strong evidence for a correlated signal, the data does not strongly prefer either correlation signature, with Bayes factors ∼2 when comparing HD to ST correlations, and ∼1 for HD plus ST correlations to HD correlations alone. However, when modeled alongside HD correlations, the amplitude and spectral index posteriors for ST correlations are uninformative, with the HD process accounting for the vast majority of the total signal. Using the optimal statistic, a frequentist technique that focuses on the pulsar-pair cross-correlations, we find median signal-to-noise ratios of 5.0 for HD and 4.6 for ST correlations when fit for separately, and median signal-to-noise ratios of 3.5 for HD and 3.0 for ST correlations when fit for simultaneously. While the signal-to-noise ratios for each of the correlations are comparable, the estimated amplitude and spectral index for HD are a significantly better fit to the total signal, in agreement with our Bayesian analysis

How to Detect an Astrophysical Nanohertz Gravitational Wave Background

\ua9 2023. The Author(s). Published by the American Astronomical Society.Analyses of pulsar timing data have provided evidence for a stochastic gravitational wave background in the nanohertz frequency band. The most plausible source of this background is the superposition of signals from millions of supermassive black hole binaries. The standard statistical techniques used to search for this background and assess its significance make several simplifying assumptions, namely (i) Gaussianity, (ii) isotropy, and most often, (iii) a power-law spectrum. However, a stochastic background from a finite collection of binaries does not exactly satisfy any of these assumptions. To understand the effect of these assumptions, we test standard analysis techniques on a large collection of realistic simulated data sets. The data-set length, observing schedule, and noise levels were chosen to emulate the NANOGrav 15 yr data set. Simulated signals from millions of binaries drawn from models based on the Illustris cosmological hydrodynamical simulation were added to the data. We find that the standard statistical methods perform remarkably well on these simulated data sets, even though their fundamental assumptions are not strictly met. They are able to achieve a confident detection of the background. However, even for a fixed set of astrophysical parameters, different realizations of the universe result in a large variance in the significance and recovered parameters of the background. We also find that the presence of loud individual binaries can bias the spectral recovery of the background if we do not account for them

Role of integrin receptors for fibronectin, collagen and laminin in the regulation of ovarian carcinoma functions in response to a matrix microenvironment

Integrins play an important role in cellular matrix interactions requisite for cancer cell adhesion, growth, migration and invasion. In this study, we have investigated the expression of integrin subunits alpha 3, alpha 6, alpha v and beta 1 in normal ovaries, benign ovarian tumors and ovarian carcinomas of different pathological grades. The expression of these integrins in ovarian cancer cell lines was also investigated, and their role in sustaining proliferation, adhesion, migration and invasion in cohort with the activation of signaling pathways in response to extracellular matrices (ECM) was evaluated. We demonstrate a differential expression pattern of alpha 3, alpha 6, alpha v and beta 1 integrin subunits in ovarian carcinomas compared to normal ovaries and benign ovarian tumors. Ovarian cancer cell lines (Hey, Ovcar3 and Peo.36) demonstrated significantly high expression of alpha 3, alpha 6, alpha v and beta 1 integrin subunits. A significant increase in proliferation and adhesion (P < 0.05) in response to collagen 1 (Coll) and laminin (LM), ligands for integrin receptor alpha 3 beta 1 and alpha 6 beta 1 was observed in ovarian cancer cell lines. On the other hand, fibronectin (FN), a receptor for alpha v beta 1 integrin, increased proliferation in all ovarian cancer cell lines studied but only enhanced adhesion in Hey cell line (P < 0.05). Neutralizing antibodies against alpha 3, alpha 6, alpha v and beta 1 integrin subunits inhibited ECM-induced proliferation, but increased adhesion to ECM was inhibited by beta 1 integrin subunit antibody. No suppression of Coll, LM and FN-induced (Hey cells only) adhesion was observed in the presence of alpha 3 or alpha v subunit antibodies but LM-induced adhesion was inhibited by blocking alpha 6 subunit functions. LM, FN and Coll enhanced chemotactic migration in Hey cells, but direct invasion across ECM was observed only in the presence of LM and Coll. Blocking antibodies against alpha 3, alpha 6 and beta 1 integrin subunits inhibited both chemotactic migration and invasion of Hey cells in response to respective ECM. Adhesion of ovarian cancer cells to FN, Coll and LM activated Ras, Erk and Akt pathways. Neutralizing alpha v and beta 1 functions did not inhibit FN-induced activation of Ras and Erk pathways but inhibited the Akt pathway. On the other hand, antibodies against alpha 6 and beta 1 subunits, but not alpha 3 subunit, inhibited LM-induced activation of Ras but did not inhibit the downstream Akt pathway. Neutralizing beta 1 subunit function however, inhibited LM-induced Erk activation. Coll-induced activation of Ras, Erk and Akt pathways was inhibited by alpha 3 and beta 1 integrin subunit antibodies. These results indicate that alpha 3 beta 1, alpha v beta 1 and alpha 6 beta 1 integrin mediate proliferation, adhesion, migration and invasion of ovarian cancer cells in response to ECM and targeting these integrins to modulate integrin-ECM interactions in tumor cells may be a promising tool to reduce the dissemination of ovarian carcinoma in vivo