اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدTesting Gravity Theories In The Radiative Regime Using Pulsar Timing Arrays
118
0
0.0
(
0
)
تأليف
K.J.Lee
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
General relativity has predicted the existence of gravitational waves (GW), which are waves of the distortions of space-time with two degrees of polarization and the propagation speed of light. Alternative theories predict more polarizations, up to a maximum of six, and possible deviation of propagation speed from the light speed. The present paper reviews recent proposals to test the gravity theories in the radiation regime by observing GWs using pulsar timing arrays.
قيم البحث
اقرأ أيضاً
In this paper, we focus on testing gravity theories in the radiative regime using pulsar timing array observations. After reviewing current techniques to measure the dispersion and alternative polarization of gravitational waves, we extend the framew
ork to the most general situations, where the combinations of a massive graviton and alternative polarization modes are considered. The atlas of the Hellings-Downs functions is completed by the new calculations for these dispersive alternative polarization modes. We find that each mode and corresponding graviton mass introduce characteristic features in the Hellings-Downs function. Thus, in principal, we can not only detect each polarization mode, measure the corresponding graviton mass, but also discriminate the different scenarios. In this way, we can test gravity theories in the radiative regime in a generalized fashion, and such method is a direct experiment, where one can address the gauge symmetry of the gravity theories in their linearised limits. Although current pulsar timing still lacks enough stable pulsars and sensitivity for such practices, we expect that future telescopes with larger collecting area could make such experiments be feasible.
Massive gravitons are features of some alternatives to general relativity. This has motivated experiments and observations that, so far, have been consistent with the zero mass graviton of general relativity, but further tests will be valuable. A bas
is for new tests may be the high sensitivity gravitational wave experiments that are now being performed, and the higher sensitivity experiments that are being planned. In these experiments it should be feasible to detect low levels of dispersion due to nonzero graviton mass. One of the most promising techniques for such a detection may be the pulsar timing program that is sensitive to nano-Hertz gravitational waves. Here we present some details of such a detection scheme. The pulsar timing response to a gravitational wave background with the massive graviton is calculated, and the algorithm to detect the massive graviton is presented. We conclude that, with 90% probability, massles gravitons can be distinguished from gravitons heavier than $3times 10^{-22}$ eV (Compton wave length $lambda_{rm g}=4.1 times 10^{12}$ km), if biweekly observation of 60 pulsars are performed for 5 years with pulsar RMS timing accuracy of 100 ns. If 60 pulsars are observed for 10 years with the same accuracy, the detectable graviton mass is reduced to $5times 10^{-23}$ eV ($lambda_{rm g}=2.5 times 10^{13}$ km); for 5-year observations of 100 or 300 pulsars, the sensitivity is respectively $2.5times 10^{-22}$ ($lambda_{rm g}=5.0times 10^{12}$ km) and $10^{-22}$ eV ($lambda_{rm g}=1.2times 10^{13}$ km). Finally, a 10-year observation of 300 pulsars with 100 ns timing accuracy would probe graviton masses down to $3times 10^{-23}$ eV ($lambda_{rm g}=4.1times 10^{13}$ km).
The opening of the gravitational wave window by ground-based laser interferometers has made possible many new tests of gravity, including the first constraints on polarization. It is hoped that within the next decade pulsar timing will extend the win
dow by making the first detections in the nano-Hertz frequency regime. Pulsar timing offers several advantages over ground-based interferometers for constraining the polarization of gravitational waves due to the many projections of the polarization pattern provided by the different lines of sight to the pulsars, and the enhanced response to longitudinal polarizations. Here we show that existing results from pulsar timing arrays can be used to place stringent limits on the energy density of longitudinal stochastic gravitational waves. Paradoxically however, we find that longitudinal modes will be very difficult to detect due to the large variance in the pulsar-pulsar correlation patterns for these modes. Existing upper limits on the power spectrum of pulsar timing residuals imply that the amplitude of vector longitudinal and scalar longitudinal modes at frequencies of 1/year are constrained: ${cal A}_{rm VL} < 4.1times 10^{-16}$ and ${cal A}_{rm SL} < 3.7times 10^{-17}$, while the bounds on the energy density for a scale invariant cosmological background are: $Omega_{rm VL}h^2 < 3.5 times 10^{-11}$ and $Omega_{rm SL}h^2 < 3.2 times 10^{-13}$.
Modified theories of gravity have received a renewed interest due to their ability to account for the cosmic acceleration. In order to satisfy the solar system tests of gravity, these theories need to include a screening mechanism that hides the modi
fications on small scales. One popular and well-studied theory is chameleon gravity. Our own galaxy is necessarily screened, but less dense dwarf galaxies may be unscreened and their constituent stars can exhibit novel features. In particular, unscreened stars are brighter, hotter and more ephemeral than screened stars in our own galaxy. They also pulsate with a shorter period. In this essay, we exploit these new features to constrain chameleon gravity to levels three orders of magnitude lower the previous measurements. These constraints are currently the strongest in the literature.
We explore the potential of Pulsar Timing Arrays (PTAs) such as NANOGrav, EPTA, and PPTA to detect the Stochastic Gravitational Wave Background (SGWB) in theories of massive gravity. In General Relativity, the function describing the dependence of th
e correlation between the arrival times of signals from two pulsars on the angle between them is known as the Hellings-Downs curve. We compute the analogous overlap reduction function for massive gravity, including the additional polarization states and the correction due to the mass of the graviton, and compare the result with the Hellings-Downs curve. The primary result is a complete analytical form for the analog Hellings-Downs curve, providing a starting point for future numerical studies aimed at a detailed comparison between PTA data and the predictions of massive gravity. We study both the massless limit and the stationary limit as checks on our calculation, and discuss how our formalism also allows us to study the impact of massive spin-2 dark matter candidates on data from PTAs.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
