Using Pulsar Parameter Drifts to Detect Sub-Nanohertz Gravitational Waves

Gravitational waves with frequencies below 1~nHz are notoriously difficult to detect. With periods exceeding current experimental lifetimes, they induce slow drifts in observables rather than periodic correlations. Observables with well-known intrinsic contributions provide a means to probe this regime. In this work, we demonstrate the viability of using observed pulsar timing parameters to discover such "ultralow" frequency gravitational waves, presenting two complementary observables for which the systematic shift induced by ultralow-frequency gravitational waves can be extracted. Using existing data for these parameters, we search the ultralow frequency regime for continuous-wave signals, finding a sensitivity near the expected prediction from inspirals of supermassive black holes. We do not see an excess in the data, setting a limit on the strain of $1.3 \times 10 ^{ - 12}$ at $450~{\rm pHz}$ with a sensitivity dropping approximately quadratically with frequency until $10~{\rm pHz}$. Our search method opens a new frequency range for gravitational wave detection and has profound implications for astrophysics, cosmology, and particle physics.Comment: 20 pages, 4 figures, 4 appendices; v2: updated to match PR

Searching For Stochastic Gravitational Waves Below a Nanohertz

The stochastic gravitational-wave background is imprinted on the times of arrival of radio pulses from millisecond pulsars. Traditional pulsar timing analyses fit a timing model to each pulsar and search the residuals of the fit for a stationary time correlation. This method breaks down at gravitational-wave frequencies below the inverse observation time of the array; therefore, existing analyses restrict their searches to frequencies above 1 nHz. An effective method to overcome this challenge is to study the correlation of secular drifts of parameters in the pulsar timing model itself. In this paper, we show that timing model correlations are sensitive to sub-nanohertz stochastic gravitational waves and perform a search using existing measurements of binary spin-down rates and pulsar spin-decelerations. We do not observe a signal at our present sensitivity, constraining the stochastic gravitational-wave relic energy density to $\Omega_\text{GW} ( f ) < 3.9 \times 10 ^{ - 9}$ at 450 pHz with sensitivity which scales as the frequency squared until approximately 10 pHz. We place additional limits on the amplitude of a power-law spectrum of $A_\star \lesssim 8\times10^{-15}$ for the spectral index expected from supermassive black hole binaries, $\gamma = 13/3$. If a detection of a supermassive black hole binary signal above 1 nHz is confirmed, this search method will serve as a critical complementary probe of the dynamics of galaxy evolution.Comment: 13 pages, 2 figure

Crkva sv. Gjorgja u Podgorici

Opis crkve sv. Gjorgja kraj današnje Podgorice u Crnoj Gori, čije vrijeme postanka nije poznato. Opis daje sliku građevine prije posljednje prepravke koja je izvedena 1931. god. Tada je, pod izgovorom da je potrebno osiguranje zbog pukotina u svodovima, cijela građevina nakarađena debelim betonskim slojem i dr. radovima kojima je gotovo onemogućeno ispitivanje ovog malog ali značajnog povijesno-arhitektonskog spomenika iz naše davne prošlosti (4 slike i 1 tabla

Biochemical and Single-Molecule Fluorescence Characterization of MutS and MutS Homolog Protein-DNA Interactions

MutS and MutS homologs are the proteins within the prokaryote and eukaryote DNA mismatch repair pathways that are the responsible for recognizing single base-base mismatches or insertion/deletion errors in newly replicated DNA. Specific interactions between MutS and these DNA defects trigger a cascade of protein-protein interactions that ultimately results in repair of the DNA error. Mutations in the homologs of the MutS and MutL repair proteins involved the recognition and initiation of post replicative DNA mismatch repair are associated with ~80% of Hereditary Nonpolyposis Colorectal Cancer (HNPCC) occurrences. The mechanism by which MutS recognizes mismatch DNA and initiates of downstream repair is not well understood. In this dissertation, I present biochemical and single molecule fluorescence studies of Thermus aquaticus (Taq) MutS as well as human and yeast MutS heterodimer homologs (hMSH2-MSH6 and yMsh2-Msh6) protein-DNA interactions in an effort to better understand DNA mismatch recognition and repair. Single molecule fluorescence methodologies were employed to compare the MutS-DNA interactions of wild type Taq MutS with a mutant of Taq MutS, E41A. Previous work has shown that Taq MutS adopts a complex series of conformations when interaction with mismatch DNA with a bent state and an unbent state being the dominant states. In this work, the kinetics of interconversion among bending states was determined to vary widely for different mismatches. Further, the E41A mutant, which is known to have specific deficiencies in repair capability, demonstrates altered DNA bending kinetics on DNA mismatches that correlate with its repair deficiencies. Despite structural similarities, the biochemical properties of prokaryotic MutS and eukaryotic MSH2-MSH6 (MutSα) have been shown to vary. Characterization of MutSα-DNA interactions has been limited. In order to compare the prokaryote and eukaryote, the protein-DNA interactions of wild type human MutSα (hMutSα) protein as well as two HNPCC separation-of-function mutants, MSH2WT-MSH6T1219D and MSH2G674A-MSH6WT were characterized. In contrast to Taq MutS-DNA interactions, I observed few hMutα-DNA conformational changes suggesting a difference in the mechanism of MMR initiation between prokaryotes and eukaryotes. I further determined singular trapped conformational states for each HNPCC mutant that may be linked to MMR deficiency for each.Doctor of Philosoph