The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Sabee Molloi - One of the best experts on this subject based on the ideXlab platform.
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Breast tissue decomposition with Spectral Distortion correction: a postmortem study.
Medical physics, 2014Co-Authors: Huanjun Ding, Bo Zhao, Pavlo Baturin, Farnaz Behroozi, Sabee MolloiAbstract:Purpose: To investigate the feasibility of an accurate measurement of water, lipid, and protein composition of breast tissue using a photon-counting Spectral computed tomography (CT) with Spectral Distortion corrections. Methods: Thirty-eight postmortem breasts were imaged with a cadmium-zinc-telluride-based photon-counting Spectral CT system at 100 kV. The energy-resolving capability of the photon-counting detector was used to separate photons into low and high energy bins with a splitting energy of 42 keV. The estimated mean glandular dose for each breast ranged from 1.8 to 2.2 mGy. Two Spectral Distortion correction techniques were implemented, respectively, on the raw images to correct the nonlinear detector response due to pulse pileup and charge-sharing artifacts. Dual energy decomposition was then used to characterize each breast in terms of water, lipid, and protein content. In the meantime, the breasts were chemically decomposed into their respective water, lipid, and protein components to provide a gold standard for comparison with dual energy decomposition results. Results: The accuracy of the tissue compositional measurement with Spectral CT was determined by comparing to the reference standard from chemical analysis. The averaged root-mean-square error in percentage composition was reduced from 15.5% to 2.8% after Spectral Distortion corrections. Conclusions: The results indicate that Spectral CT can be used to quantify the water, lipid, and protein content in breast tissue. The accuracy of the compositional analysis depends on the applied Spectral Distortion correction technique.
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tu f 18c 01 breast tissue decomposition using Spectral ct after Distortion correction
Medical Physics, 2014Co-Authors: Huanjun Ding, Bo Zhao, Pavlo Baturin, Michael Klopfer, F Masaki, Sabee MolloiAbstract:Purpose: To investigate the feasibility of accurate breast tissue compositional characterization by using Spectral-Distortion-corrected dual energy images from a photon-counting Spectral CT. Methods: Thirty eight postmortem breasts were imaged with a Cadmium-Zinc-Telluride (CZT)-based photon-counting Spectral CT system at beam energy of 100 kVp. The energy-resolved detector sorted photons into low and high energy bins with a splitting energy of 42 keV. The estimated mean glandular dose (MGD) for each breast was approximately 2.0 mGy. Dual energy technique was used to decompose breast tissue into water, lipid, and protein contents. Two image-based methods were investigated to improve the accuracy of tissue compositional characterization. The first method simply limited the recorded spectra up to 90 keV. This reduced the pulse pile-up artifacts but it has some dose penalty. The second method corrected the Spectral information of all measured photons by using a Spectral Distortion correction technique. Breasts were then chemically decomposed into their respective water, lipid, and protein contents, which was used as the reference standard. The accuracy of the tissue compositional measurement with Spectral CT was evaluated by the root-mean-square (RMS) errors in percentage composition. Results: The errors in quantitative material decomposition were significantly reduced after the appropriate image processing methods.more » As compared to the chemical analysis as the reference standard, the averages of the RMS errors were estimated to be 15.5%, 3.3%, and 2.8% for the raw, energy-limited, and Spectral-corrected images, respectively. Conclusion: Spectral CT can be used to accurately quantify the water, lipid, and protein contents in breast tissues by implementing a Spectral Distortion correction algorithm. The tissue compositional information can potentially improve the sensitivity and specificity for breast cancer diagnosis.« less
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th a 217bcd 03 Spectral Distortion correction for photon counting x ray detectors
Medical Physics, 2012Co-Authors: Huanjun Ding, Sabee MolloiAbstract:Purpose: To investigate the feasibility of using an image‐based method to correct for Spectral Distortions from photon‐counting detectors for their application in breast computed tomography(CT).Methods: The polyenergetic incident spectrum was simulated with the tungstenanode Spectral model. Experiments were performed on a Cadmium‐Zinc‐Telluride (CZT) photon‐counting detector with five energy thresholds. BR12 phantoms of various thicknesses were used for calibration. A non‐linear function was selected to fit the count correlation between the simulated and the measured spectra in the calibration process. To evaluate the proposed Spectral Distortion correction method, both the corrected counts and the effective attenuation coefficients were compared to the simulated values for polymethyl methacrylate (PMMA) phantoms of 8.7 mm, 48.8 mm and 100.0 mm. The feasibility of applying the proposed method to quantitative material decomposition was tested using a dual‐energy imaging technique with a three‐material phantom that consisted of water, lipid and protein.Results: The implementation of the proposed method reduced the relative RMS error of the output counts in the five energy bins with respect to the simulated incident counts from 23.0%, 33.0% and 54.0% to 1.2%, 1.8% and 7.7% for 8.7 mm, 48.8 mm and 100.0 mm PMMA phantoms, respectively. The accuracy of the effective attenuation coefficient of PMMA estimate was also improved with the proposed Spectral Distortion correction. Finally, the relative RMS error of water, lipid and protein decompositions in dual‐ energy imaging was significantly reduced from 53.4% to 6.8% after correction was applied. Conclusions: The study demonstrated that the proposed method can effectively reduce the Spectral Distortions caused by various artifacts, including pulse pileup and charge sharing effects. It may be used as a generalized procedure for the spectrum Distortion correction of different photon‐counting detectors in clinical breast CT systems.
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image based Spectral Distortion correction for photon counting x ray detectors
Medical Physics, 2012Co-Authors: Huanjun Ding, Sabee MolloiAbstract:Purpose: To investigate the feasibility of using an image-based method to correct for Distortions induced by various artifacts in the x-ray spectrum recorded with photon-counting detectors for their application in breast computed tomography (CT). Methods: The polyenergetic incident spectrum was simulated with the tungsten anode Spectral model using the interpolating polynomials (TASMIP) code and carefully calibrated to match the x-ray tube in this study. Experiments were performed on a Cadmium-Zinc-Telluride (CZT) photon-counting detector with five energy thresholds. Energy bins were adjusted to evenly distribute the recorded counts above the noise floor. BR12 phantoms of various thicknesses were used for calibration. A nonlinear function was selected to fit the count correlation between the simulated and the measured spectra in the calibration process. To evaluate the proposed Spectral Distortion correction method, an empirical fitting derived from the calibration process was applied on the raw images recorded for polymethyl methacrylate (PMMA) phantoms of 8.7, 48.8, and 100.0 mm. Both the corrected counts and the effective attenuation coefficient were compared to the simulated values for each of the five energy bins. The feasibility of applying the proposed method to quantitative material decomposition was tested using a dual-energy imaging technique with a three-material phantom that consisted of water, lipid, and protein. The performance of the Spectral Distortion correction method was quantified using the relative root-mean-square (RMS) error with respect to the expected values from simulations or areal analysis of the decomposition phantom. Results: The implementation of the proposed method reduced the relative RMS error of the output counts in the five energy bins with respect to the simulated incident counts from 23.0%, 33.0%, and 54.0% to 1.2%, 1.8%, and 7.7% for 8.7, 48.8, and 100.0 mm PMMA phantoms, respectively. The accuracy of the effective attenuation coefficient of PMMA estimate was also improved with the proposed Spectral Distortion correction. Finally, the relative RMS error of water, lipid, and protein decompositions in dual-energy imaging was significantly reduced from 53.4% to 6.8% after correction was applied. Conclusions: The study demonstrated that dramatic Distortions in the recorded raw image yielded from a photon-counting detector could be expected, which presents great challenges for applying the quantitative material decomposition method in Spectral CT. The proposed semi-empirical correction method can effectively reduce these errors caused by various artifacts, including pulse pileup and charge sharing effects. Furthermore, rather than detector-specific simulation packages, the method requires a relatively simple calibration process and knowledge about the incident spectrum. Therefore, it may be used as a generalized procedure for the Spectral Distortion correction of different photon-counting detectors in clinical breast CT systems.
Rishi Khatri - One of the best experts on this subject based on the ideXlab platform.
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new cmb Spectral Distortion constraints on decaying dark matter with full evolution of electromagnetic cascades before recombination
Physical Review D, 2019Co-Authors: Sandeep Kumar Acharya, Rishi KhatriAbstract:Current constraints on energy injection in the form of energetic particles before the epoch of recombination using CMB Spectral Distortions assume that all energy goes into $y$ and $\mu$-type Distortions. We revisit these constraints with exact calculations of the Spectral Distortions by evolving the electromagnetic cascades. The actual Spectral Distortion differs in shape and amplitude from the $y$-type Distortion and depends on the energy and nature of injected particles. The constraints on the energy injection processes such as dark matter decay can be relaxed by as much as a factor of 5.
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forecasts for cmb mu and i type Spectral Distortion constraints on the primordial power spectrum on scales 8 k 10 4 mpc 1 with the future pixie like experiments
arXiv: Cosmology and Nongalactic Astrophysics, 2013Co-Authors: Rishi Khatri, R SunyaevAbstract:Silk damping at redshifts 1.5 x 10^4 < z < 2 x 10^6 erases CMB anisotropies on scales corresponding to the comoving wavenumbers 8 < k < 10^4 Mpc^-1 (10^5 < \ell < 10^8). This dissipated energy is gained by the CMB monopole, creating Distortions from a blackbody in the CMB spectrum of the \mu-type and the i-type. We study, using Fisher matrices, the constraints we can get from measurements of these Spectral Distortions on the primordial power spectrum from future experiments such as Pixie, and how these constraints change as we change the frequency resolution and the sensitivity of the experiment. We show that the additional information in the shape of the $i$-type Distortions, in combination with the \mu-type Distortions, allows us to break the degeneracy between the amplitude and the Spectral index of the power spectrum on these scales and leads to much tighter constraints. We quantify the information contained in both the \mu-type Distortions and the i-type Distortions taking into account the partial degeneracy with the y-type Distortions and the temperature of the blackbody part of the CMB. We also calculate the constraints possible on the primordial power spectrum when the Spectral Distortion information is combined with the CMB anisotropies measured by the WMAP, SPT, ACT and Planck experiments.
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forecasts for cmb μ and i type Spectral Distortion constraints on the primordial power spectrum on scales 8 less sim k less sim 10 4 mpc 1 with the future pixie like experiments
Journal of Cosmology and Astroparticle Physics, 2013Co-Authors: Rishi Khatri, R SunyaevAbstract:Silk damping at redshifts 1.5 × 104z2 × 106 erases CMB anisotropies on scales corresponding to the comoving wavenumbers 8k104 Mpc−1 (105l108). This dissipated energy is gained by the CMB monopole, creating Distortions from a blackbody in the CMB spectrum of the μ-type and the i-type. We study, using Fisher matrices, the constraints we can get from measurements of these Spectral Distortions on the primordial power spectrum from future experiments such as Pixie, and how these constraints change as we change the frequency resolution and the sensitivity of the experiment. We show that the additional information in the shape of the i-type Distortions, in combination with the μ-type Distortions, allows us to break the degeneracy between the amplitude and the Spectral index of the power spectrum on these scales and leads to much tighter constraints. We quantify the information contained in both the μ-type Distortions and the i-type Distortions taking into account the partial degeneracy with the y-type Distortions and the temperature of the blackbody part of the CMB. We also calculate the constraints possible on the primordial power spectrum when the Spectral Distortion information is combined with the CMB anisotropies measured by the WMAP, SPT, ACT and Planck experiments.
Huanjun Ding - One of the best experts on this subject based on the ideXlab platform.
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Breast tissue decomposition with Spectral Distortion correction: a postmortem study.
Medical physics, 2014Co-Authors: Huanjun Ding, Bo Zhao, Pavlo Baturin, Farnaz Behroozi, Sabee MolloiAbstract:Purpose: To investigate the feasibility of an accurate measurement of water, lipid, and protein composition of breast tissue using a photon-counting Spectral computed tomography (CT) with Spectral Distortion corrections. Methods: Thirty-eight postmortem breasts were imaged with a cadmium-zinc-telluride-based photon-counting Spectral CT system at 100 kV. The energy-resolving capability of the photon-counting detector was used to separate photons into low and high energy bins with a splitting energy of 42 keV. The estimated mean glandular dose for each breast ranged from 1.8 to 2.2 mGy. Two Spectral Distortion correction techniques were implemented, respectively, on the raw images to correct the nonlinear detector response due to pulse pileup and charge-sharing artifacts. Dual energy decomposition was then used to characterize each breast in terms of water, lipid, and protein content. In the meantime, the breasts were chemically decomposed into their respective water, lipid, and protein components to provide a gold standard for comparison with dual energy decomposition results. Results: The accuracy of the tissue compositional measurement with Spectral CT was determined by comparing to the reference standard from chemical analysis. The averaged root-mean-square error in percentage composition was reduced from 15.5% to 2.8% after Spectral Distortion corrections. Conclusions: The results indicate that Spectral CT can be used to quantify the water, lipid, and protein content in breast tissue. The accuracy of the compositional analysis depends on the applied Spectral Distortion correction technique.
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tu f 18c 01 breast tissue decomposition using Spectral ct after Distortion correction
Medical Physics, 2014Co-Authors: Huanjun Ding, Bo Zhao, Pavlo Baturin, Michael Klopfer, F Masaki, Sabee MolloiAbstract:Purpose: To investigate the feasibility of accurate breast tissue compositional characterization by using Spectral-Distortion-corrected dual energy images from a photon-counting Spectral CT. Methods: Thirty eight postmortem breasts were imaged with a Cadmium-Zinc-Telluride (CZT)-based photon-counting Spectral CT system at beam energy of 100 kVp. The energy-resolved detector sorted photons into low and high energy bins with a splitting energy of 42 keV. The estimated mean glandular dose (MGD) for each breast was approximately 2.0 mGy. Dual energy technique was used to decompose breast tissue into water, lipid, and protein contents. Two image-based methods were investigated to improve the accuracy of tissue compositional characterization. The first method simply limited the recorded spectra up to 90 keV. This reduced the pulse pile-up artifacts but it has some dose penalty. The second method corrected the Spectral information of all measured photons by using a Spectral Distortion correction technique. Breasts were then chemically decomposed into their respective water, lipid, and protein contents, which was used as the reference standard. The accuracy of the tissue compositional measurement with Spectral CT was evaluated by the root-mean-square (RMS) errors in percentage composition. Results: The errors in quantitative material decomposition were significantly reduced after the appropriate image processing methods.more » As compared to the chemical analysis as the reference standard, the averages of the RMS errors were estimated to be 15.5%, 3.3%, and 2.8% for the raw, energy-limited, and Spectral-corrected images, respectively. Conclusion: Spectral CT can be used to accurately quantify the water, lipid, and protein contents in breast tissues by implementing a Spectral Distortion correction algorithm. The tissue compositional information can potentially improve the sensitivity and specificity for breast cancer diagnosis.« less
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th a 217bcd 03 Spectral Distortion correction for photon counting x ray detectors
Medical Physics, 2012Co-Authors: Huanjun Ding, Sabee MolloiAbstract:Purpose: To investigate the feasibility of using an image‐based method to correct for Spectral Distortions from photon‐counting detectors for their application in breast computed tomography(CT).Methods: The polyenergetic incident spectrum was simulated with the tungstenanode Spectral model. Experiments were performed on a Cadmium‐Zinc‐Telluride (CZT) photon‐counting detector with five energy thresholds. BR12 phantoms of various thicknesses were used for calibration. A non‐linear function was selected to fit the count correlation between the simulated and the measured spectra in the calibration process. To evaluate the proposed Spectral Distortion correction method, both the corrected counts and the effective attenuation coefficients were compared to the simulated values for polymethyl methacrylate (PMMA) phantoms of 8.7 mm, 48.8 mm and 100.0 mm. The feasibility of applying the proposed method to quantitative material decomposition was tested using a dual‐energy imaging technique with a three‐material phantom that consisted of water, lipid and protein.Results: The implementation of the proposed method reduced the relative RMS error of the output counts in the five energy bins with respect to the simulated incident counts from 23.0%, 33.0% and 54.0% to 1.2%, 1.8% and 7.7% for 8.7 mm, 48.8 mm and 100.0 mm PMMA phantoms, respectively. The accuracy of the effective attenuation coefficient of PMMA estimate was also improved with the proposed Spectral Distortion correction. Finally, the relative RMS error of water, lipid and protein decompositions in dual‐ energy imaging was significantly reduced from 53.4% to 6.8% after correction was applied. Conclusions: The study demonstrated that the proposed method can effectively reduce the Spectral Distortions caused by various artifacts, including pulse pileup and charge sharing effects. It may be used as a generalized procedure for the spectrum Distortion correction of different photon‐counting detectors in clinical breast CT systems.
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image based Spectral Distortion correction for photon counting x ray detectors
Medical Physics, 2012Co-Authors: Huanjun Ding, Sabee MolloiAbstract:Purpose: To investigate the feasibility of using an image-based method to correct for Distortions induced by various artifacts in the x-ray spectrum recorded with photon-counting detectors for their application in breast computed tomography (CT). Methods: The polyenergetic incident spectrum was simulated with the tungsten anode Spectral model using the interpolating polynomials (TASMIP) code and carefully calibrated to match the x-ray tube in this study. Experiments were performed on a Cadmium-Zinc-Telluride (CZT) photon-counting detector with five energy thresholds. Energy bins were adjusted to evenly distribute the recorded counts above the noise floor. BR12 phantoms of various thicknesses were used for calibration. A nonlinear function was selected to fit the count correlation between the simulated and the measured spectra in the calibration process. To evaluate the proposed Spectral Distortion correction method, an empirical fitting derived from the calibration process was applied on the raw images recorded for polymethyl methacrylate (PMMA) phantoms of 8.7, 48.8, and 100.0 mm. Both the corrected counts and the effective attenuation coefficient were compared to the simulated values for each of the five energy bins. The feasibility of applying the proposed method to quantitative material decomposition was tested using a dual-energy imaging technique with a three-material phantom that consisted of water, lipid, and protein. The performance of the Spectral Distortion correction method was quantified using the relative root-mean-square (RMS) error with respect to the expected values from simulations or areal analysis of the decomposition phantom. Results: The implementation of the proposed method reduced the relative RMS error of the output counts in the five energy bins with respect to the simulated incident counts from 23.0%, 33.0%, and 54.0% to 1.2%, 1.8%, and 7.7% for 8.7, 48.8, and 100.0 mm PMMA phantoms, respectively. The accuracy of the effective attenuation coefficient of PMMA estimate was also improved with the proposed Spectral Distortion correction. Finally, the relative RMS error of water, lipid, and protein decompositions in dual-energy imaging was significantly reduced from 53.4% to 6.8% after correction was applied. Conclusions: The study demonstrated that dramatic Distortions in the recorded raw image yielded from a photon-counting detector could be expected, which presents great challenges for applying the quantitative material decomposition method in Spectral CT. The proposed semi-empirical correction method can effectively reduce these errors caused by various artifacts, including pulse pileup and charge sharing effects. Furthermore, rather than detector-specific simulation packages, the method requires a relatively simple calibration process and knowledge about the incident spectrum. Therefore, it may be used as a generalized procedure for the Spectral Distortion correction of different photon-counting detectors in clinical breast CT systems.
Subinoy Das - One of the best experts on this subject based on the ideXlab platform.
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the effects of the small scale behaviour of dark matter power spectrum on cmb Spectral Distortion
arXiv: Cosmology and Nongalactic Astrophysics, 2017Co-Authors: Abir Sarkar, Shiv K Sethi, Subinoy DasAbstract:After numerous astronomical and experimental searches, the precise particle nature of dark matter is still unknown. The standard Weakly Interacting Massive Particle(WIMP) dark matter, despite successfully explaining the large-scale features of the universe, has long-standing small-scale issues. The Spectral Distortion in the Cosmic Microwave Background(CMB) caused by Silk damping in the pre-recombination era allows one to access information on a range of small scales $0.3 \, {\rm Mpc} < k < 10^4 \, \rm Mpc^{-1}$, whose dynamics can be precisely described using linear theory. In this paper, we investigate the possibility of using the Silk damping induced CMB Spectral Distortion as a probe of the small-scale power. We consider four suggested alternative dark matter candidates---Warm Dark Matter (WDM), Late Forming Dark Matter, Ultra Light Axion dark matter and Charged Decaying Dark Matter; the matter power in all these models deviate significantly from the $\Lambda$CDM model at small scales. We compute the Spectral Distortion of CMB for these alternative models and compare our results with the $\Lambda$CDM model. We show that the main impact of alternative models is to alter the sub-horizon evolution of the Newtonian potential which affects the late-time behaviour of Spectral Distortion of CMB. The $y$-parameter diminishes by a few percent as compared to the $\Lambda$CDM model for a range of parameters of these models: LFDM for formation redshift $z_f = 10^5$ (7\%); WDM for mass $m_{\rm wdm} = 1 \, \rm keV$ (2\%); CHDM for decay redshift $z_{\rm decay} = 10^5$ (5\%); ULA for mass $m_a = 10^{-24} \, \rm eV$ (3\%). We also briefly discuss the detectability of this deviation in light of the upcoming CMB experiment PIXIE, which might have the sensitivity to detect this signal from the pre-recombination phase.
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the effects of the small scale behaviour of dark matter power spectrum on cmb Spectral Distortion
Journal of Cosmology and Astroparticle Physics, 2017Co-Authors: Abir Sarkar, Shiv K Sethi, Subinoy DasAbstract:After numerous astronomical and experimental searches, the precise particle nature of dark matter is still unknown. The standard Weakly Interacting Massive Particle(WIMP) dark matter, despite successfully explaining the large-scale features of the universe, has long-standing small-scale issues. The Spectral Distortion in the Cosmic Microwave Background(CMB) caused by Silk damping in the pre-recombination era allows one to access information on a range of small scales 0.3 Mpc < k < 10(4) Mpc(-1), whose dynamics can be precisely described using linear theory. In this paper, we investigate the possibility of using the Silk damping induced CMB Spectral Distortion as a probe of the small-scale power. We consider four suggested alternative dark matter candidates-Warm Dark Matter (WDM), Late Forming Dark Matter, Ultra Light Axion dark matter and Charged Decaying Dark Matter; the matter power in all these models deviate significantly from the Lambda CDM model at small scales. We compute the Spectral Distortion of CMB for these alternative models and compare our results with the Lambda CDM model. We show that the main impact of alternative models is to alter the sub-horizon evolution of the Newtonian potential which affects the late-time behaviour of Spectral Distortion of CMB. The y-parameter diminishes by a few percent as compared to the Lambda CDM model for a range of parameters of these models: LFDM for formation redshift z(f) = 10(5) (7\textbackslash%); WDM for mass m(wdm) = 1 keV (2\textbackslash%); CHDM for decay redshift z(decay) = 10(5) (5\textbackslash%); ULA for mass m(a) = 10(-24) eV (3\textbackslash%). We also briefly discuss the detectability of this deviation in light of the upcoming CMB experiment PIXIE, which might have the sensitivity to detect this signal from the pre-recombination phase.
Jens Chluba - One of the best experts on this subject based on the ideXlab platform.
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Spectral Distortion constraints on photon injection from low mass decaying particles
Monthly Notices of the Royal Astronomical Society, 2021Co-Authors: Jens Chluba, Boris Bolliet, Richard A BattyeAbstract:Spectral Distortions (SDs) of the cosmic microwave background (CMB) provide a powerful tool for studying particle physics. Here we compute the Distortion signals from decaying particles that convert directly into photons at different epochs during cosmic history, focusing on injection energies $E_\mathrm{inj}\lesssim 20\,\mathrm{keV}$. We deliver a comprehensive library of SD solutions that can be used to study a wide range of particle physics scenarios. We use {\tt CosmoTherm} to compute the SD signals, including effects on the ionization history and opacities of the Universe. We also consider the effect of blackbody-induced stimulated decay, which can modify the injection history significantly. Then, we use data from COBE/FIRAS and EDGES to constrain the properties of the decaying particles. We explore scenarios where these provide a dark matter (DM) candidate or constitute only a small fraction of DM. We complement the SD constraints with CMB anisotropy constraints, highlighting new effects from injections at very-low photon energies ($h\nu\lesssim 10^{-4}\,\mathrm{eV}$). Our model-independent constraints exhibit rich structures in the lifetime-energy domain, covering injection energies $E_\mathrm{inj}\simeq 10^{-10}\mathrm{eV}-10\mathrm{keV}$ and lifetimes $\tau_X\simeq 10^5\,\mathrm{s}-10^{33}\mathrm{s}$. We discuss the constraints on axions and axion-like particles that convert directly into two photons, revising existing SD constraints in the literature. Our limits are competitive with other constraints for axion masses $m_a c^2\gtrsim 27\,\mathrm{eV}$ and we find that simple estimates based on the overall energetics are generally inaccurate. Future CMB spectrometers could significantly improve the obtained constraints, thus providing an important complementary probe of early-universe particle physics.
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evolution of cmb Spectral Distortion anisotropies and tests of primordial non gaussianity
Monthly Notices of the Royal Astronomical Society, 2017Co-Authors: Jens Chluba, Emanuela Dimastrogiovanni, Mustafa A Amin, Marc KamionkowskiAbstract:Anisotropies in Distortions to the frequency spectrum of the cosmic microwave background (CMB) can be created through spatially varying heating processes in the early Universe. For instance, the dissipation of small-scale acoustic modes does create Distortion anisotropies, in particular for non-Gaussian primordial perturbations. In this work, we derive approximations that allow describing the associated Distortion field. We provide a systematic formulation of the problem using Fourier-space window functions, clarifying and generalizing previous approximations. Our expressions highlight the fact that the amplitudes of the Spectral-Distortion fluctuations induced by non-Gaussianity depend also on the homogeneous value of those Distortions. Absolute measurements are thus required to obtain model-independent Distortion constraints on primordial non-Gaussianity. We also include a simple description for the evolution of Distortions through photon diffusion, showing that these corrections can usually be neglected. Our formulation provides a systematic framework for computing higher order correlation functions of Distortions with CMB temperature anisotropies and can be extended to describe correlations with polarization anisotropies.
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tests of the cmb temperature redshift relation cmb Spectral Distortions and why adiabatic photon production is hard
Monthly Notices of the Royal Astronomical Society, 2014Co-Authors: Jens ChlubaAbstract:In the expanding Universe, the average temperature of the cosmic microwave background (CMB) is expected to depend like TCMB ∝ (1 + z) on redshift z. Adiabatic photon production (or destruction) or deviations from isotropy and homogeneity could modify this scaling and several observational tests have been carried out in response. Here, we explain why ‘adiabatic’ conditions are extremely di ffi cult to establish in the redshift range targeted by these tests. Thus, instead of leading to a simple rescaling of the C MB temperature, a Spectral Distortion should be produced, which can be constrained using COBE/FIRAS. For scenarios with late photon production, tests of the temperature-redshift relation (TRR) should therefore be reinterpreted as weak Spectral Distortion limits, directl y probing the energy dependence of the photon production process. For inhomogeneous cosmologies, a y-type Distortion is produced, but this type of Distortion can be created in several ways. Here, we briefly discuss possible effects that may help disentangling different contributions to the Distortion signal, finding this to be very challenging. We furthermore argue that tests of the TRR using the SZ effect have limited applicability and that for non-gravitational chan ges to the TRR the CMB anisotropy spectrum should exhibit an additional y-type dependence.
