We have derived precise analytic expressions for the quasinormal modes of test scalar, and Dirac fields in the background of the dilaton black hole. To achieve this, we employ the higher-order WKB expansion in terms of $1/ell$. A comparison between the analytic formulas and time-domain integration reveals that the analytic approach generally yields more accurate results than the numerical results previously published using the lower-order WKB approach. We demonstrate that in the eikonal regime, test fields adhere to the correspondence between null geodesics and eikonal quasinormal modes.
{"title":"Quasinormal Modes of Dilaton Black Holes: Analytic approximations","authors":"Zainab Malik","doi":"arxiv-2409.09872","DOIUrl":"https://doi.org/arxiv-2409.09872","url":null,"abstract":"We have derived precise analytic expressions for the quasinormal modes of\u0000test scalar, and Dirac fields in the background of the dilaton black hole. To\u0000achieve this, we employ the higher-order WKB expansion in terms of $1/ell$. A\u0000comparison between the analytic formulas and time-domain integration reveals\u0000that the analytic approach generally yields more accurate results than the\u0000numerical results previously published using the lower-order WKB approach. We\u0000demonstrate that in the eikonal regime, test fields adhere to the\u0000correspondence between null geodesics and eikonal quasinormal modes.","PeriodicalId":501041,"journal":{"name":"arXiv - PHYS - General Relativity and Quantum Cosmology","volume":"2 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142250734","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Bouncing cosmologies, while offering a compelling alternative to inflationary models, face challenges from the growth of vector perturbations during the contracting phase. While linear vector instabilities can be avoided with specific initial conditions or the absence of vector degrees of freedom, we demonstrate the significant role of secondary vector perturbations generated by non-linear interactions with scalar fluctuations. Our analysis reveals that in a broad class of single-field matter bounce scenarios, these secondary vector perturbations inevitably get unacceptably large amplitudes, provided the curvature fluctuations are consistent with cosmic microwave background observations. This finding underscores the crucial importance of scalar-induced vector perturbations in bouncing cosmology and highlights the need for further investigation into their potential impact on the viability of these models.
{"title":"Constraining matter bounce scenario from scalar-induced vector perturbations","authors":"Mian Zhu, Chao Chen","doi":"arxiv-2409.09458","DOIUrl":"https://doi.org/arxiv-2409.09458","url":null,"abstract":"Bouncing cosmologies, while offering a compelling alternative to inflationary\u0000models, face challenges from the growth of vector perturbations during the\u0000contracting phase. While linear vector instabilities can be avoided with\u0000specific initial conditions or the absence of vector degrees of freedom, we\u0000demonstrate the significant role of secondary vector perturbations generated by\u0000non-linear interactions with scalar fluctuations. Our analysis reveals that in\u0000a broad class of single-field matter bounce scenarios, these secondary vector\u0000perturbations inevitably get unacceptably large amplitudes, provided the\u0000curvature fluctuations are consistent with cosmic microwave background\u0000observations. This finding underscores the crucial importance of scalar-induced\u0000vector perturbations in bouncing cosmology and highlights the need for further\u0000investigation into their potential impact on the viability of these models.","PeriodicalId":501041,"journal":{"name":"arXiv - PHYS - General Relativity and Quantum Cosmology","volume":"52 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142250783","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We present a new family of regular black holes (RBH) in Pure Lovelock gravity, where the energy density is determined by the gravitational vacuum tension, which varies for each value of $n$ in each Lovelock case. A notable feature of our model is that the regular solution closely resembles the vacuum solution before reaching the event horizon. For odd $n$, the transverse geometry is spherical, with phase transitions occurring during evaporation, and the final state of this process is a remnant. For even $n$, the transverse geometry in non trivial and corresponds to a hyperboloid. In the case of $d=2n+1$ with even $n$, we find an RBH without a dS core and no inner horizon (whose presence has been recently debated in the literature due to the question of whether its presence is unstable or not), and no phase transitions. For $d>2n+1$ with even $n$, the RBH possesses both an event horizon and a cosmological horizon and no inner horizon. The existence of the cosmological horizon arises without the usual requirement of a positive cosmological constant. From both numerical and analytical analysis, we deduce that as the event horizon expands and the cosmological horizon contracts, thermodynamic equilibrium is achieved in a remnant when the two horizons coincide.
{"title":"Pure Lovelock Gravity regular black holes","authors":"Milko Estrada, Rodrigo Aros","doi":"arxiv-2409.09559","DOIUrl":"https://doi.org/arxiv-2409.09559","url":null,"abstract":"We present a new family of regular black holes (RBH) in Pure Lovelock\u0000gravity, where the energy density is determined by the gravitational vacuum\u0000tension, which varies for each value of $n$ in each Lovelock case. A notable\u0000feature of our model is that the regular solution closely resembles the vacuum\u0000solution before reaching the event horizon. For odd $n$, the transverse\u0000geometry is spherical, with phase transitions occurring during evaporation, and\u0000the final state of this process is a remnant. For even $n$, the transverse\u0000geometry in non trivial and corresponds to a hyperboloid. In the case of\u0000$d=2n+1$ with even $n$, we find an RBH without a dS core and no inner horizon\u0000(whose presence has been recently debated in the literature due to the question\u0000of whether its presence is unstable or not), and no phase transitions. For\u0000$d>2n+1$ with even $n$, the RBH possesses both an event horizon and a\u0000cosmological horizon and no inner horizon. The existence of the cosmological\u0000horizon arises without the usual requirement of a positive cosmological\u0000constant. From both numerical and analytical analysis, we deduce that as the\u0000event horizon expands and the cosmological horizon contracts, thermodynamic\u0000equilibrium is achieved in a remnant when the two horizons coincide.","PeriodicalId":501041,"journal":{"name":"arXiv - PHYS - General Relativity and Quantum Cosmology","volume":"40 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142250731","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The conditions for the existence of the Chapman-Enskog first-order solution to the Boltzmann equation for a dilute gas are examined from two points of view. The traditional procedure is contrasted with a somehow more formal approach based on the properties of the linearized collision operator. It is shown that both methods lead to the same integral equation in the non-relativistic scenario. Meanwhile, for relativistic systems, the source term in the integral equation adopts two different forms. However, as we explain, this does not lead to an inconsistency. In fact, the constitutive equations that are obtained from both methods are shown to be equivalent within relativistic first-order theories. The importance of stating invariant definitions for the transport coefficients in this context is emphasized.
{"title":"Existence of the Chapman-Enskog solution and its relation with first-order dissipative fluid theories","authors":"A. L. García-Perciante, A. R. Méndez, O. Sarbach","doi":"arxiv-2409.08976","DOIUrl":"https://doi.org/arxiv-2409.08976","url":null,"abstract":"The conditions for the existence of the Chapman-Enskog first-order solution\u0000to the Boltzmann equation for a dilute gas are examined from two points of\u0000view. The traditional procedure is contrasted with a somehow more formal\u0000approach based on the properties of the linearized collision operator. It is\u0000shown that both methods lead to the same integral equation in the\u0000non-relativistic scenario. Meanwhile, for relativistic systems, the source term\u0000in the integral equation adopts two different forms. However, as we explain,\u0000this does not lead to an inconsistency. In fact, the constitutive equations\u0000that are obtained from both methods are shown to be equivalent within\u0000relativistic first-order theories. The importance of stating invariant\u0000definitions for the transport coefficients in this context is emphasized.","PeriodicalId":501041,"journal":{"name":"arXiv - PHYS - General Relativity and Quantum Cosmology","volume":"47 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142250786","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Davide Mancieri, Luca Broggi, Matteo Bonetti, Alberto Sesana
Extreme mass ratio inspirals (EMRIs) are anticipated to be primary gravitational wave sources for LISA (Laser Interferometer Space Antenna). They form in dense nuclear clusters when a compact object (CO) is captured by the central massive black holes (MBHs) due to frequent two-body interactions among orbiting objects. We present a novel Monte Carlo approach to evolve the post-Newtonian (PN) equations of motion of a CO orbiting an MBH accounting for two-body relaxation locally on the fly, without the assumption of orbit-averaging. We estimate the fraction $S(a_0)$ of EMRIs to total captures (including direct plunges, DPs) as a function of the initial semi-major axis $a_0$ for COs around MBHs of $M_bulletin[10^4,{rm M}_odot,4times10^6,{rm M}_odot]$. Previous results indicate $S(a_0)rightarrow 0$ at large $a_0$, with a sharp transition from EMRIs to DPs around a critical scale $a_{rm c}$. This notion has been recently challenged for low-mass MBHs, with EMRIs forming at $agg a_{rm c}$, the so-called "cliffhangers''. Our simulations confirm their existence, at larger numbers than previously expected. Cliffhangers start to appear for $M_bulletlesssim3times 10^5,{rm M}_odot$ and can account for up to 55% of the overall EMRIs formed. We find $S(a_0)gg 0$ for $agg a_{rm c}$, reaching values as high as 0.6 for $M_bullet=10^4,{rm M}_odot$, much larger than previously found. We find that the PN description of the system greatly enhances the number of EMRIs by shifting $a_{rm c}$ to larger values at all MBH masses, and that the local treatment of relaxation significantly boosts the number of cliffhangers for small MBHs. Our work shows the limitations of standard assumptions for estimating EMRI formation rates, most importantly their dynamical models. Future estimates of rates and properties of EMRIs detectable by LISA should account for these improvements.
极端质量比吸气（EMRIs）预计将成为激光干涉仪空间天线（LISA）的主要引力波源。由于轨道天体之间频繁的双体相互作用，当一个紧凑天体（CO）被中心大质量黑洞（MBHs）捕获时，它们就会在致密核星团中形成。我们提出了一种新颖的蒙特卡洛方法来演化绕 MBH 运行的 CO 的后牛顿（PN）运动方程，无需假定轨道平均。对于围绕M_bulletin[10^4,{rmM}_odot,4times10^6,{rm M}_odot]$的MBH的一氧化碳，我们估算了作为初始半长轴$a_0$函数的EMRIs占总捕获量（包括直接坠落，DPs）的分数$S(a_0)$。以前的结果表明，在大尺度 $a_0$ 时，$S(a_0)rightarrow 0$，在临界尺度 $a_{rm c}$ 附近，会从 EMRIs 急剧过渡到 DPs。这一概念最近在低质量MBHs上受到了挑战，EMRIs在$agg a_{rm c}$时形成，即所谓的 "悬崖"。我们的模拟证实了它们的存在，而且数量比之前预期的要多。悬崖开始出现于$M_bulletlesssim3times 10^5,{rm M}_odot$，并且可以占到整个EMRI形成的55%。我们发现$S(a_0)gg 0$为$agg a_{rm c}$，当$M_bullet=10^4,{rm M}_odot$时，数值高达0.6，远远大于之前发现的数值。我们发现，系统的PN描述通过在所有MBH质量下将$a_{rm c}$移动到更大的值，极大地增加了EMRI的数量，而且对弛豫的局部处理极大地增加了小MBH的悬案数量。我们的工作显示了用于估计EMRI形成率的标准假设的局限性，其中最重要的是它们的动力学模型。未来对 LISA 可探测到的 EMRI 的速率和性质的估计应考虑到这些改进。
{"title":"Hanging on the cliff: EMRI formation with local two-body relaxation and post-Newtonian dynamics","authors":"Davide Mancieri, Luca Broggi, Matteo Bonetti, Alberto Sesana","doi":"arxiv-2409.09122","DOIUrl":"https://doi.org/arxiv-2409.09122","url":null,"abstract":"Extreme mass ratio inspirals (EMRIs) are anticipated to be primary\u0000gravitational wave sources for LISA (Laser Interferometer Space Antenna). They\u0000form in dense nuclear clusters when a compact object (CO) is captured by the\u0000central massive black holes (MBHs) due to frequent two-body interactions among\u0000orbiting objects. We present a novel Monte Carlo approach to evolve the\u0000post-Newtonian (PN) equations of motion of a CO orbiting an MBH accounting for\u0000two-body relaxation locally on the fly, without the assumption of\u0000orbit-averaging. We estimate the fraction $S(a_0)$ of EMRIs to total captures\u0000(including direct plunges, DPs) as a function of the initial semi-major axis\u0000$a_0$ for COs around MBHs of $M_bulletin[10^4,{rm\u0000M}_odot,4times10^6,{rm M}_odot]$. Previous results indicate\u0000$S(a_0)rightarrow 0$ at large $a_0$, with a sharp transition from EMRIs to DPs\u0000around a critical scale $a_{rm c}$. This notion has been recently challenged\u0000for low-mass MBHs, with EMRIs forming at $agg a_{rm c}$, the so-called\u0000\"cliffhangers''. Our simulations confirm their existence, at larger numbers\u0000than previously expected. Cliffhangers start to appear for\u0000$M_bulletlesssim3times 10^5,{rm M}_odot$ and can account for up to 55% of\u0000the overall EMRIs formed. We find $S(a_0)gg 0$ for $agg a_{rm c}$, reaching\u0000values as high as 0.6 for $M_bullet=10^4,{rm M}_odot$, much larger than\u0000previously found. We find that the PN description of the system greatly\u0000enhances the number of EMRIs by shifting $a_{rm c}$ to larger values at all\u0000MBH masses, and that the local treatment of relaxation significantly boosts the\u0000number of cliffhangers for small MBHs. Our work shows the limitations of\u0000standard assumptions for estimating EMRI formation rates, most importantly\u0000their dynamical models. Future estimates of rates and properties of EMRIs\u0000detectable by LISA should account for these improvements.","PeriodicalId":501041,"journal":{"name":"arXiv - PHYS - General Relativity and Quantum Cosmology","volume":"5 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142250785","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Wouter G. J. van Zeist, Gijs Nelemans, Simon F. Portegies Zwart, Jan J. Eldridge
We use the stellar evolution code BPASS and the gravitational wave simulation code LEGWORK to simulate populations of compact binaries that may be detected by the in-development space-based gravitational wave (GW) detector LISA. Specifically, we simulate the Magellanic Clouds and binary populations mimicking several globular clusters, neglecting dynamical effects. We find that the Magellanic Clouds would have a handful of detectable sources each, but for globular clusters the amount of detectable sources would be less than one. We compare our results to earlier research and find that our predicted numbers are several tens of times lower than calculations using the stellar evolution code BSE that take dynamical effects into account, but also calculations using the stellar evolution code SeBa for the Magellanic Clouds. This correlates with earlier research which compared BPASS models for GW sources in the Galactic disk with BSE models and found a similarly sized discrepancy. We analyse and explain this discrepancy as being caused by differences between the stellar evolution codes, particularly in the treatment of mass transfer and common-envelope events in binaries, where in BPASS mass transfer is more likely to be stable and tends to lead to less orbital shrinkage in the common-envelope phase than in other codes. This difference results in fewer compact binaries with periods short enough to be detected by LISA existing in the BPASS population. For globular clusters, we conclude that the impact of dynamical effects is uncertain from the literature, but the differences in stellar evolution have an effect of a factor of a few tens.
我们使用恒星演化代码 BPASS 和引力波模拟代码 LEGWORK 来模拟可能会被正在开发中的空间引力波（GW）探测器 LISA 探测到的紧凑双星群。我们发现，麦哲伦云会有少量可探测源，而球状星团可探测源的数量会少于一个。我们将我们的结果与早先的研究结果进行了比较，发现我们预测的数量比使用恒星演化代码BSE（考虑了动力学效应）的计算结果低几十倍，同时也比使用恒星演化代码SeBa对麦哲伦云的计算结果低几十倍。这与早先的研究结果相吻合，早先的研究将银河盘中的 GW 源的 BPASS 模型与 BSE 模型进行了比较，发现了类似大小的差异。我们分析并解释了这种差异，认为它是由恒星演化代码之间的差异造成的，特别是在处理质量转移和双星中的共包层事件方面，在BPASS中，质量转移更有可能是稳定的，在共包层阶段往往会比其他代码导致更少的轨道收缩。这种差异导致 BPASS 群体中存在的周期短到足以被 LISA 探测到的紧凑双星数量较少。对于球状星团，我们的结论是，从文献来看，动力学效应的影响并不确定，但恒星旋转的差异会产生几十倍的影响。
{"title":"Evaluating the gravitational wave detectability of globular clusters and the Magellanic Clouds for LISA","authors":"Wouter G. J. van Zeist, Gijs Nelemans, Simon F. Portegies Zwart, Jan J. Eldridge","doi":"arxiv-2409.09159","DOIUrl":"https://doi.org/arxiv-2409.09159","url":null,"abstract":"We use the stellar evolution code BPASS and the gravitational wave simulation\u0000code LEGWORK to simulate populations of compact binaries that may be detected\u0000by the in-development space-based gravitational wave (GW) detector LISA.\u0000Specifically, we simulate the Magellanic Clouds and binary populations\u0000mimicking several globular clusters, neglecting dynamical effects. We find that\u0000the Magellanic Clouds would have a handful of detectable sources each, but for\u0000globular clusters the amount of detectable sources would be less than one. We\u0000compare our results to earlier research and find that our predicted numbers are\u0000several tens of times lower than calculations using the stellar evolution code\u0000BSE that take dynamical effects into account, but also calculations using the\u0000stellar evolution code SeBa for the Magellanic Clouds. This correlates with\u0000earlier research which compared BPASS models for GW sources in the Galactic\u0000disk with BSE models and found a similarly sized discrepancy. We analyse and\u0000explain this discrepancy as being caused by differences between the stellar\u0000evolution codes, particularly in the treatment of mass transfer and\u0000common-envelope events in binaries, where in BPASS mass transfer is more likely\u0000to be stable and tends to lead to less orbital shrinkage in the common-envelope\u0000phase than in other codes. This difference results in fewer compact binaries\u0000with periods short enough to be detected by LISA existing in the BPASS\u0000population. For globular clusters, we conclude that the impact of dynamical\u0000effects is uncertain from the literature, but the differences in stellar\u0000evolution have an effect of a factor of a few tens.","PeriodicalId":501041,"journal":{"name":"arXiv - PHYS - General Relativity and Quantum Cosmology","volume":"5 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142250733","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We consider the Kepler two-body problem in the presence of a cosmological constant Lambda. Several dimensionless parameters characterizing the possible orbit typologies are used to identify open and closed trajectories. The qualitative picture of the two-body motion is described and critical parameters of the problem are found.
{"title":"Orbital precession and other properties of two-body motion in the presence of dark energy","authors":"Gennady S. Bisnovatyi-Kogan, Marco Merafina","doi":"arxiv-2409.11427","DOIUrl":"https://doi.org/arxiv-2409.11427","url":null,"abstract":"We consider the Kepler two-body problem in the presence of a cosmological\u0000constant Lambda. Several dimensionless parameters characterizing the possible\u0000orbit typologies are used to identify open and closed trajectories. The\u0000qualitative picture of the two-body motion is described and critical parameters\u0000of the problem are found.","PeriodicalId":501041,"journal":{"name":"arXiv - PHYS - General Relativity and Quantum Cosmology","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142250787","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In a recent paper: ``On the time dependency of $a_0$" the authors claim that they have tested ``one of the predictions of the Scale Invariant Vacuum (SIV) theory on MOND" by studying the dependence of the Modified Newtonian Dynamics (MOND) acceleration at two data sets, low-$z$ ($3.2times10^{-4}le zle 3.2times10^{-2}$) and high-$z$ ($0.5le zle 2.5$). They claim ``both samples show a dependency of $a_0$ from $z$". Here, the work mentioned above is revisited. The explicit analytic expression for the $z$-dependence of the $a_0$ within the SIV theory is given. Furthermore, the first estimates of the $Omega_m$ within SIV theory give $Omega_{m}=0.28pm 0.04$ using the low-z data only, while a value of $Omega_{m}=0.055$ is obtained using both data sets. This much lower $Omega_m$ leaves no room for non-baryonic matter! Unlike in the mentioned paper above, the slope in the $z$-dependence of $A_0=log_{10}(a_0)$ is estimated to be consistent with zero Z-slope for the two data sets. Finally, the statistics of the data are consistent with the SIV predictions; in particular, the possibility of change in the sign of the slopes for the two data sets is explainable within the SIV paradigm; however, the uncertainty in the data is too big for the clear demonstration of a $z$-dependence yet.
{"title":"Elucidating the z-dependence of the MOND acceleration (a_0) within the Scale Invariant Vacuum (SIV) paradigm","authors":"Vesselin G. Gueorguiev","doi":"arxiv-2409.11425","DOIUrl":"https://doi.org/arxiv-2409.11425","url":null,"abstract":"In a recent paper: ``On the time dependency of $a_0$\" the authors claim that\u0000they have tested ``one of the predictions of the Scale Invariant Vacuum (SIV)\u0000theory on MOND\" by studying the dependence of the Modified Newtonian Dynamics\u0000(MOND) acceleration at two data sets, low-$z$ ($3.2times10^{-4}le zle\u00003.2times10^{-2}$) and high-$z$ ($0.5le zle 2.5$). They claim ``both samples\u0000show a dependency of $a_0$ from $z$\". Here, the work mentioned above is\u0000revisited. The explicit analytic expression for the $z$-dependence of the $a_0$\u0000within the SIV theory is given. Furthermore, the first estimates of the\u0000$Omega_m$ within SIV theory give $Omega_{m}=0.28pm 0.04$ using the low-z\u0000data only, while a value of $Omega_{m}=0.055$ is obtained using both data\u0000sets. This much lower $Omega_m$ leaves no room for non-baryonic matter! Unlike\u0000in the mentioned paper above, the slope in the $z$-dependence of\u0000$A_0=log_{10}(a_0)$ is estimated to be consistent with zero Z-slope for the\u0000two data sets. Finally, the statistics of the data are consistent with the SIV\u0000predictions; in particular, the possibility of change in the sign of the slopes\u0000for the two data sets is explainable within the SIV paradigm; however, the\u0000uncertainty in the data is too big for the clear demonstration of a\u0000$z$-dependence yet.","PeriodicalId":501041,"journal":{"name":"arXiv - PHYS - General Relativity and Quantum Cosmology","volume":"65 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142250789","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In the summer of 2023, the pulsar timing arrays (PTAs) announced a compelling evidence for the existence of a nanohertz stochastic gravitational wave background (SGWB). Despite this breakthrough, however, several critical questions remain unanswered: What is the source of the signal? How can cosmic variance be accounted for? To what extent can we constrain nanohertz gravity? When will individual supermassive black hole binaries become observable? And how can we achieve a stronger detection? These open questions have spurred significant interests in PTA science, making this an opportune moment to revisit the astronomical and theoretical foundations of the field, as well as the data analysis techniques employed. In this review, we focus on the theoretical aspects of the SGWB as detected by PTAs. We provide a comprehensive derivation of the expected signal and its correlation, presented in a pedagogical manner, while also addressing current constraints. Looking ahead, we explore future milestones in the field, with detailed discussions on emerging theoretical considerations such as cosmic variance, the cumulants of the one- and two-point functions, subluminal gravitational waves, and the anisotropy and polarization of the SGWB.
{"title":"Charting the Nanohertz Gravitational Wave Sky with Pulsar Timing Arrays","authors":"Reginald Christian Bernardo, Kin-Wang Ng","doi":"arxiv-2409.07955","DOIUrl":"https://doi.org/arxiv-2409.07955","url":null,"abstract":"In the summer of 2023, the pulsar timing arrays (PTAs) announced a compelling\u0000evidence for the existence of a nanohertz stochastic gravitational wave\u0000background (SGWB). Despite this breakthrough, however, several critical\u0000questions remain unanswered: What is the source of the signal? How can cosmic\u0000variance be accounted for? To what extent can we constrain nanohertz gravity?\u0000When will individual supermassive black hole binaries become observable? And\u0000how can we achieve a stronger detection? These open questions have spurred\u0000significant interests in PTA science, making this an opportune moment to\u0000revisit the astronomical and theoretical foundations of the field, as well as\u0000the data analysis techniques employed. In this review, we focus on the\u0000theoretical aspects of the SGWB as detected by PTAs. We provide a comprehensive\u0000derivation of the expected signal and its correlation, presented in a\u0000pedagogical manner, while also addressing current constraints. Looking ahead,\u0000we explore future milestones in the field, with detailed discussions on\u0000emerging theoretical considerations such as cosmic variance, the cumulants of\u0000the one- and two-point functions, subluminal gravitational waves, and the\u0000anisotropy and polarization of the SGWB.","PeriodicalId":501041,"journal":{"name":"arXiv - PHYS - General Relativity and Quantum Cosmology","volume":"3 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142199287","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Dark matter, an important portion of compact objects, can influence different phenomena in neutron stars. The spontaneous scalarization in the scalar-tensor gravity has been proposed for neutron stars. Here, we investigate the spontaneous scalarization in dark matter admixed neutron stars. Applying the dark matter equations of state, we calculate the structure of scalarized neutron stars containing dark matter. The dark matter equations of state are based on observational data from the rotational curves of galaxies and the fermionic self-interacting dark matter. Our results verify that the spontaneous scalarization is affected by the dark matter pressure in neutron stars. Depending on the central density of scalarized dark matter admixed neutron stars, the dark matter pressure alters the central scalar field. The increase of dark matter pressure in low-density scalarized stars amplifies the central scalar field. However, the pressure of dark matter in high-density scalarized stars suppresses the central scalar field. Our calculations confirm that the stars in the merger event GW170817 and in the low-mass X-ray binary 4U 1820-30 can be scalarized dark matter admixed neutron stars.
{"title":"Effects of Dark Matter on the Spontaneous Scalarization in Neutron Stars","authors":"Fahimeh Rahimi, Zeinab Rezaei","doi":"arxiv-2409.07328","DOIUrl":"https://doi.org/arxiv-2409.07328","url":null,"abstract":"Dark matter, an important portion of compact objects, can influence different\u0000phenomena in neutron stars. The spontaneous scalarization in the scalar-tensor\u0000gravity has been proposed for neutron stars. Here, we investigate the\u0000spontaneous scalarization in dark matter admixed neutron stars. Applying the\u0000dark matter equations of state, we calculate the structure of scalarized\u0000neutron stars containing dark matter. The dark matter equations of state are\u0000based on observational data from the rotational curves of galaxies and the\u0000fermionic self-interacting dark matter. Our results verify that the spontaneous\u0000scalarization is affected by the dark matter pressure in neutron stars.\u0000Depending on the central density of scalarized dark matter admixed neutron\u0000stars, the dark matter pressure alters the central scalar field. The increase\u0000of dark matter pressure in low-density scalarized stars amplifies the central\u0000scalar field. However, the pressure of dark matter in high-density scalarized\u0000stars suppresses the central scalar field. Our calculations confirm that the\u0000stars in the merger event GW170817 and in the low-mass X-ray binary 4U 1820-30\u0000can be scalarized dark matter admixed neutron stars.","PeriodicalId":501041,"journal":{"name":"arXiv - PHYS - General Relativity and Quantum Cosmology","volume":"2 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142199237","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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