1,720,969 research outputs found
Extreme mass ratio inspirals with spinning secondary: A detailed study of equatorial circular motion
No full textExtreme-mass-ratio inspirals (EMRIs) detectable by the future Laser Interferometer Space Antenna provide a unique way to test general relativity and fundamental physics. Motivated by this possibility, here we study in detail the EMRI dynamics in the presence of a spinning secondary, collecting and extending various results that appeared in previous work and also providing useful intermediate steps and new relations for the first time. We present the results of a frequency-domain code that computes gravitational-wave fluxes and the adiabatic orbital evolution for the case of circular, equatorial orbits with (anti)aligned spins. The spin of the secondary starts to affect the gravitational-wave phase at the first post-adiabatic order (as does the first-order conservative self-force) and introduces a detectable dephasing, which can be used to measure it at the 5-25% level, depending on individual spins. In a companion paper we discuss the implication of this effect for tests of the Kerr bound
Reheating and dark radiation after fibre inflation
Full text linkWe study perturbative reheating at the end of fibre inflation where the inflaton is a closed string modulus with a Starobinsky-like potential. We first derive the spectral index n s and the tensor-to-scalar ratio r as a function of the number of efoldings and the parameter R which controls slow-roll breaking corrections. We then compute the inflaton couplings and decay rates into ultra-light bulk axions and visible sector fields on D7-branes wrapping the inflaton divisor. This leads to a reheating temperature of order 10 10 GeV which requires 52 efoldings. Ultra-light axions contribute to dark radiation even if Δ N eff is almost negligible in the generic case where the visible sector D7-stack supports a non-zero gauge flux. If the parameter R is chosen to be small enough, n s 0.965 is then in perfect agreement with current observations while r turns out to be of order r 0.007. If instead the flux on the inflaton divisor is turned off, Δ N eff 0.6 which, when used as a prior for Planck data, requires n s 0.99. After R is fixed to obtain such a value of n s , primordial gravity waves are larger since r 0.01
Model independent tests of the Kerr bound with extreme mass ratio inspirals
Full text linkAn outstanding prediction of general relativity is the fact that the angular momentum S of an isolated black hole with mass μ is limited by the Kerr bound, S≤Gμ2/c. Testing this cornerstone is challenging due to the difficulty in modeling spinning compact objects that violate this bound. We argue that precise, model-independent tests can be achieved by measuring gravitational waves from an extreme mass ratio inspiral around a supermassive object, one of the main targets of the future LISA mission. In the extreme mass ratio limit, the dynamics of the small compact object depends only on its multipole moments, which are free parameters. At variance with the comparable-mass case, accurate waveforms are valid also when the spin of the small object greatly exceeds the Kerr bound. By computing the orbital dephasing and the gravitational-wave signal emitted by a spinning point particle in circular, nonprecessing, equatorial motion around a Kerr black hole, we estimate that LISA will be able to measure the spin of the small compact object at the level of 10%. Together with mass measurements, this will allow for theory-agnostic, unprecedented constraints on string-theory inspired objects such as “superspinars”, almost in their entire parameter space
Interferometria radar per lo studio dell'evoluzione del movimento gravitativo profondo di Beauregard
No full textAssessing the detectability of the secondary spin in extreme mass-ratio inspirals with fully relativistic numerical waveforms
No full textExtreme mass-ratio inspirals (EMRIs) detectable by the Laser Inteferometric Space Antenna (LISA) are unique probes of astrophysics and fundamental physics. Parameter estimation for these sources is challenging, especially because the waveforms are long, complicated, known only numerically, and slow to compute in the most relevant regime, where the dynamics is relativistic. We perform a time-consuming Fisher-matrix error analysis of the EMRI parameters using fully relativistic numerical waveforms to leading order in an adiabatic expansion on a Kerr background, taking into account the motion of the LISA constellation, higher harmonics, and also including the leading correction from the spin of the secondary in the postadiabatic approximation. We pay particular attention to the convergence of the numerical derivatives in the Fisher matrix and to the numerical stability of the covariance matrix, which for some systems requires computing the numerical waveforms with approximately 90-digit precision. Our analysis confirms previous results (obtained with approximated but much more computationally efficient waveforms) for the measurement errors on the binary's parameters. We also show that the inclusion of higher harmonics improves the errors on the luminosity distance and on the orbital angular momentum angles by one order and two orders of magnitude, respectively, which might be useful to identify the environments where EMRIs live. We particularly focus on the measurability of the spin of the secondary, confirming that, for spin-aligned EMRIs on quasicircular orbits, it cannot be measured with sufficient accuracy. However, due to correlations, its inclusion in the waveform model can deteriorate the accuracy on the measurements of other parameters by orders of magnitude, unless a physically motivated prior on the secondary spin is imposed
Monitoring of the Beauregard landslide (Aosta Valley, Italy) using advanced and conventional techniques
No full textAn advanced monitoring technique, based on radar interferometry and implemented by using a ground-based
instrumentation (GBInSAR) has been applied for monitoring the Beauregard Deep Seated Gravitational Slope
Deformation. This landslide is located in the Aosta Valley (on the Dora di Valgrisenche river), in northwestern
Italy, and impinges on a 132 m high concrete arch-gravity dam. This is recognized to have relevant
implications in terms of civil protection and poses important territorial and environmental issues.
The poor rock mass conditions of the left abutment slope were reported in the fifties, during dam
construction. Since 2002, additional geological, hydrogeological and geotechnical investigations have
underlined the presence of a deep seated shear zone up to 20 m thick, at the landslide toe. Continuous
conventional monitoring over a time span of more than 50 years of both the slope and the dam has allowed to
gain insights into the understanding of the behaviour of the basal portion of the slope, with very limited and
uncertain point-wise displacement monitored in the upper sector.
The GBInSAR monitoring technique has allowed to obtain multi-temporal surface deformations of the upper
portion of the landslide, discovering the presence of a main sector in motion, previously unknown, characterized by a total displacement of 45 mm over 4 months. The results of radar monitoring have been validated by comparing with topographic measurements carried out by an automatic total station on 4 targets located at the toe of the slope
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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