by jsendak | Jan 19, 2024 | GR & QC Articles
Recent works have uncovered an excess signal in the parity-odd four-point
correlation function measured from the BOSS spectroscopic galaxy survey. If
physical in origin, this could indicate evidence for new parity-breaking
processes in the scalar sector, most likely from inflation. At heart, these
studies compare the observed four-point correlator to the distribution obtained
from parity-conserving mock galaxy surveys; if the simulations underestimate
the covariance of the data, noise fluctuations may be misinterpreted as a
signal. To test this, we reanalyse the BOSS CMASS + LOWZ parity-odd dataset
with the noise distribution modeled using the newly developed GLAM-Uchuu suite
of mocks. These comprise full N-body simulations that follow the evolution of
$2000^3$ dark matter particles in a $Lambda$CDM universe, and represent a
significant upgrade compared to the formerly MultiDark-Patchy mocks, which were
based on an alternative (non N-body) gravity solver. We find no significant
evidence for parity-violation in the BOSS dataset (with a baseline detection
significance of $1.4sigma$), suggesting that the former signal ($>3.5sigma$
with our data cuts) could be caused by an underestimation of the covariance in
MultiDark-Patchy. The significant differences between results obtained with the
two sets of BOSS-calibrated galaxy catalogs showcases the heightened
sensitivity of beyond-two-point analyses to the treatment of non-linear effects
and indicates that previous constraints may suffer from large systematic
uncertainties.
Recent studies have found an excess signal in the parity-odd four-point correlation function measured from the BOSS spectroscopic galaxy survey. This excess signal could be evidence of new parity-breaking processes in the scalar sector, possibly caused by inflation.
To determine if this signal is physical or if it could be due to noise fluctuations, the BOSS CMASS + LOWZ parity-odd dataset is reanalyzed. The noise distribution in this analysis is modeled using the newly developed GLAM-Uchuu suite of mocks, which are full N-body simulations that follow the evolution of dark matter particles in a $Lambda$CDM universe.
This reanalysis finds no significant evidence for parity-violation in the BOSS dataset, with a baseline detection significance of .4sigma$. This suggests that the previous signal ($>3.5sigma$ with data cuts) may have been caused by an underestimation of the covariance in the MultiDark-Patchy mocks.
The significant differences between the results obtained with the two sets of BOSS-calibrated galaxy catalogs highlight the importance of properly accounting for non-linear effects in beyond-two-point analyses. These differences also indicate that previous constraints may have large systematic uncertainties.
Future Roadmap
Looking ahead, there are several challenges and opportunities on the horizon:
1. Further Analysis
Additional analysis and investigations should be conducted to confirm these findings and verify the robustness of the conclusions. This includes exploring other datasets and performing independent analyses to validate the absence of parity-violation.
2. Improving Covariance Estimation
The underestimation of covariance in the MultiDark-Patchy mocks underscores the need for more accurate and reliable methods of estimating covariance. Developing improved covariance estimation techniques can help prevent the misinterpretation of noise fluctuations as signals, leading to more accurate and reliable measurements.
3. Refining Non-linear Effects Treatment
Beyond-two-point analyses are highly sensitive to the treatment of non-linear effects. Ongoing efforts should focus on refining and enhancing the methods used to account for these non-linear effects. This will improve the accuracy of future measurements and reduce systematic uncertainties.
4. Expanding Mock Catalogs
The use of mock catalogs, such as the GLAM-Uchuu suite, is crucial for understanding and analyzing large-scale structure data. Continuously expanding and improving these mock catalogs will enable more realistic simulations and provide better comparisons with observational data.
5. Exploring New Parity-breaking Processes
The discovery of a potential excess signal in the parity-odd four-point correlation function opens up new opportunities for exploring and understanding parity-breaking processes in the scalar sector. Future research should focus on investigating different inflationary models and studying their implications for large-scale structure formation.
By addressing these challenges and embracing the opportunities, future studies in this field can improve our understanding of the scalar sector, inflation, and the fundamental processes that govern the large-scale structure of the universe.
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by jsendak | Jan 8, 2024 | GR & QC Articles
This thesis introduces an effective theory for the long-distance behaviour of
scalar fields in de Sitter spacetime, known as the second-order stochastic
theory, with the aim of computing scalar correlation functions that are useful
in inflationary cosmology.
This thesis presents the second-order stochastic theory, which aims to compute scalar correlation functions for scalar fields in de Sitter spacetime. These correlation functions are important in inflationary cosmology. The theory provides an effective framework for understanding the long-distance behavior of scalar fields.
Conclusion
The second-order stochastic theory offers a valuable approach to studying scalar fields in de Sitter spacetime. It provides a means to calculate scalar correlation functions, which have significant implications for inflationary cosmology. By understanding the behavior of these correlation functions, we can gain insights into the dynamics of the early universe and the origin of cosmic structures.
Future Roadmap
The second-order stochastic theory opens up various avenues for future research and exploration. Here is a potential roadmap for readers interested in this area:
1. Validation and Refinement
One immediate challenge is to validate the second-order stochastic theory by comparing its predictions with observational data and existing theoretical models. This would involve analyzing cosmological datasets, such as measurements of the cosmic microwave background radiation and galaxy surveys. It may also require refining the theory to account for specific scenarios and phenomena on various scales.
2. Extension to Other Fields
While the focus of this thesis is on scalar fields, future research could explore the applicability of the second-order stochastic theory to other fields, such as vector or tensor fields. This extension would provide a more comprehensive understanding of inflationary cosmology and its broader implications.
3. Cosmological Implications
Investigating the cosmological implications of the second-order stochastic theory is another promising area of research. Understanding how these correlation functions impact the evolution of the early universe could shed light on fundamental questions, such as the nature of dark matter, the existence of primordial gravitational waves, and the generation of cosmic magnetic fields.
4. Integration with Quantum Field Theory
The second-order stochastic theory could be integrated with quantum field theory, which would enable a more rigorous treatment of the underlying physics. Exploring the connection between the stochastic theory and quantum field theory could lead to new insights and potentially reconcile any discrepancies that arise.
5. Numerical Simulations and Analytical Techniques
Developing computational tools and analytical techniques to efficiently calculate scalar correlation functions within the second-order stochastic theory is essential. This would involve utilizing powerful numerical simulation methods, improving computational algorithms, and developing analytical approximations to handle complex scenarios.
6. Experimental Tests
Finally, experimental tests could be conducted to verify the predictions made by the second-order stochastic theory. Designing and carrying out experiments that probe the properties of scalar correlation functions could provide direct evidence for the validity and accuracy of the theory, further bolstering our understanding of inflationary cosmology.
Challenges and Opportunities
While the second-order stochastic theory offers exciting possibilities, there are several challenges and opportunities to consider:
- Theoretical Complexity: The second-order stochastic theory involves intricate mathematical formalism and intricate calculations. Developing simplified frameworks and approximations would facilitate practical applications and reduce computational complexity.
- Data Availability: Acquiring accurate observational data, particularly at larger scales, may pose challenges. Collaborations with cosmological surveys and experiments would be necessary to gather reliable data for validation and testing.
- Interdisciplinary Collaboration: The success of studying scalar fields in de Sitter spacetime relies on collaboration between cosmologists, astrophysicists, mathematicians, and theoretical physicists. Building interdisciplinary partnerships can foster novel approaches and cross-pollination of ideas.
- Funding and Resources: Dedicated funding and resources are essential to support the research, development of computational tools, and organization of experimental tests. Securing funding from governmental, institutional, or private sources is crucial for advancing the field.
Summary
The second-order stochastic theory provides an effective way to compute scalar correlation functions for scalar fields in de Sitter spacetime, aiding in the study of inflationary cosmology. The future roadmap involves validating and refining the theory, extending it to other fields, investigating cosmological implications, integrating it with quantum field theory, developing computational tools, and performing experimental tests. Challenges include theoretical complexity, data availability, interdisciplinary collaboration, and securing funding and resources.
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by jsendak | Dec 30, 2023 | GR & QC Articles
Primordial magnetic fields (PMFs) are one of the plausible candidates for the
origin of the observed large-scale magnetic fields. While many proposals have
been made for the generation mechanism of PMFs by earlier studies, it remains a
subject of debate. In this paper, to obtain new insights into PMFs, we focus on
the intrinsic alignments (IAs) of galaxies induced by the vector and tensor
modes of the anisotropic stress of PMFs. The long-wavelength vector and tensor
modes locally induce the tidal gravitational fields, leading to the
characteristic distortions of the intrinsic ellipticity of galaxies. We
investigate the shear E- and B-mode power spectra induced by the magnetic
vector and tensor modes in the three-dimensional space, assuming the
combination of galaxy imaging and galaxy redshift surveys. We find that the
magnetic tensor mode dominates both the E- and B-mode spectra. In particular,
the B-mode spectrum induced by the magnetic tensor mode plays a crucial role in
constraining the amplitude of PMFs, even in the presence of the non-magnetic
scalar contribution to the B-mode spectrum arising from the one-loop effect. In
future galaxy redshift surveys, such as Euclid and Square Kilometre Array, the
minimum detectable value reaches $sim 30 , rm nG$, which can potentially get
even smaller in proportion to the number of observed galaxies and reach $sim
mathcal{O}(1 , {rm nG})$. Measuring the IAs of galaxies would be a potential
probe for PMFs in future galaxy surveys.
Primordial magnetic fields (PMFs) are a leading contender for the origin of the large-scale magnetic fields that we observe. However, the mechanism by which PMFs are generated is still a matter of debate. In this paper, we focus on the intrinsic alignments (IAs) of galaxies that are induced by the anisotropic stress of PMFs. By studying the distortions in the ellipticity of galaxies caused by the tidal gravitational fields induced by PMFs, we can gain new insights into these magnetic fields.
We examine the shear E- and B-mode power spectra that are induced by the vector and tensor modes of the PMFs in three-dimensional space. We assume a combination of galaxy imaging and galaxy redshift surveys in order to make these measurements. Our results show that the magnetic tensor mode dominates both the E- and B-mode spectra. This means that the B-mode spectrum induced by the magnetic tensor mode is particularly important for constraining the amplitude of PMFs.
In future galaxy redshift surveys, such as Euclid and Square Kilometre Array, it will be possible to detect PMFs with a minimum value of approximately 30 nG (nanogauss). This detection threshold can potentially be even smaller as the number of observed galaxies increases, reaching the order of 1 nG (nanogauss). Therefore, measuring the intrinsic alignments of galaxies could serve as a potential probe for PMFs in future galaxy surveys.
Future Roadmap: Challenges and Opportunities
Looking ahead, there are several challenges and opportunities on the horizon for studying PMFs through galaxy surveys:
1. Improving Measurement Sensitivity
The minimum detectable value for PMFs is expected to decrease as the number of observed galaxies increases. This presents an opportunity to potentially reach sensitivities on the order of 1 nG. However, improving measurement sensitivity will require advancements in data collection, analysis techniques, and instrumentation.
2. Understanding the Non-Magnetic Scalar Contribution
In our study, we find that the B-mode spectrum induced by the magnetic tensor mode is crucial for constraining PMFs. However, it is important to consider and understand the contribution of non-magnetic scalar effects to the B-mode spectrum. Further research is needed to accurately separate the contributions from different sources and mitigate any potential biases.
3. Utilizing Advanced Galaxy Surveys
The future galaxy surveys such as Euclid and Square Kilometre Array will provide valuable data for studying PMFs. These surveys will allow for the observation of a large number of galaxies, potentially improving the sensitivity for PMF detection. Leveraging the capabilities of these surveys will be essential in advancing our understanding of PMFs.
4. Broadening the Investigation
While our study focuses on the intrinsic alignments of galaxies induced by PMFs, there are many other aspects that can be explored to gain further insights. Investigating other observable effects, such as statistical correlations between galaxies and cosmic microwave background radiation, can provide additional constraints on PMFs.
In summary, the study of primordial magnetic fields through galaxy surveys holds great potential for advancing our understanding of the origin and properties of these magnetic fields. Improving measurement sensitivity, understanding non-magnetic scalar contributions, utilizing advanced surveys, and broadening the investigation are key components of the future roadmap in this field.
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