We analyse the formation and evolution of the event horizon of a black hole binary merger when th... more We analyse the formation and evolution of the event horizon of a black hole binary merger when the black holes are charged. We find that the presence of charge influences the properties of the merger and can be useful for investigating the validity of various theories of modified gravity and several proposals for dark matter candidates. It can moreover give insights into various aspects of astrophysical phenomena involving black holes, such as degeneracies in the gravitational wave parameter determination. We perform our analysis both analytically and numerically, in D = 4 dimensions, in the Extreme Mass Ratio (EMR) limit and compare the results. The development of analytical results in the EMR limit is of uttermost importance in view of the upcoming observations of the LISA interferometer. We then use our analysis to describe how the horizon evolves in time during the merger and to investigate the growth in the area of the event horizon and the duration of the merger. We moreover provide a numerical solution valid in arbitrary dimensions D ≥ 4 which could be of interest in the context of the AdS/CFT correspondence or for examining possible extensions of general relativity.
We provide the post-Newtonian (PN) waveform for binary systems in motion along generic planar orb... more We provide the post-Newtonian (PN) waveform for binary systems in motion along generic planar orbits at 2.5PN accuracy, in terms of the dynamical variables of the effective one-body (EOB) formalism. In addition to the calculation of the higher order terms for all the contributions to the waveform that have been already considered in previous avatars of EOB models, we also compute the EOB expression of the oscillatory memory terms. These are purely non-circular contributions, first appearing at 1.5PN order, that have been so far neglected in the EOB literature. This should foster their inclusion in EOB models and the definitive assessment of their role in shaping gravitational wave signals at infinity. To further promote the application of our results, we also derive associated non-circular factors according to the waveform factorization prescription of the non-circular EOB model TEOBResumS-DALI; the result is a set of ready-to-use non-circular factors that can be directly implemented as extra non-circular corrections in the waveform of TEOBResumS-DALI. 1 We recall in this respect that the PN expansion is essentially an expansion for small internal velocities of the considered system, and it is usually organized in powers of 1/c, with c being the speed of light. In particular, terms proportional to 1/c n correspond to corrections at n 2 PN order.
We present a new approach to factorize and resum the post-Newtonian (PN) waveform for generic equ... more We present a new approach to factorize and resum the post-Newtonian (PN) waveform for generic equatorial motion to be used within effective-one-body (EOB) based waveform models. The new multipolar waveform factorization improves previous prescriptions in that: (i) the generic Newtonian contribution is factored out from each multipole; (ii) the circular part is factored out and resummed using standard EOB methods and (iii) the residual, 2PN-accurate, noncircular part, and in particular the tail contribution, is additionally resummed using Padé approximants. The resulting waveform is validated in the extreme-mass-ratio limit by comparisons with nine (mostly nonspinning) numerical waveforms either from eccentric inspirals, with eccentricities up to e = 0.9, or dynamical captures. The resummation of the noncircular tail contribution is found essential to obtain excellent (0.05 rad at periastron for e = 0.9) analytical/numerical agreement and to considerably improve the prescription with just the Newtonian prefactor. In the comparable mass case, the new 2PN waveform shows only a marginal improvement over the previous Newtonian factorization, though yielding maximal unfaithfulness 10 −3 with the 28 publicly available numerical relativity simulations with eccentricity up to ∼ 0.3 (except for a single outlier that grazes 10 −2). We finally use test-particle data to validate the waveform factorization proposed by Khalil et al. [Phys. Rev. 104 (2021) 2, 024046] and conclude that its amplitude can be considered reliable (though less accurate, ∼ 6% fractional difference versus 1.5% of our method) only up to eccentricities ∼ 0.3.
We obtain a first order post-Minkowskian two-body effective potential whose post-Newtonian expans... more We obtain a first order post-Minkowskian two-body effective potential whose post-Newtonian expansion directly reproduces the Einstein-Infeld-Hoffmann potential. Post-Minkowskian potentials can be extracted from on-shell scattering amplitudes in a quantum field theory of scalar matter coupled to gravity. Previously, such potentials did not reproduce the Einstein-Infeld-Hoffmann potential without employing a suitable canonical transformation. In this work, we resolve this issue by obtaining a new expression for the first-order post-Minkowskian potential. This is accomplished by exploiting the reference frame dependence that arises in the scattering amplitude computation. Finally, as a check on our result, we demonstrate that our new potential gives the correct scattering angle.
In this paper we use the effective blackfold description of branes to extend the study of the the... more In this paper we use the effective blackfold description of branes to extend the study of the thermal BIon, a D-brane and parallel anti-D-brane connected by a wormhole with F-string charge in hot flat space, by introducing a radial boost along the brane. The boosted system behaves qualitatively differently from both the extremal and the thermal BIon considered previously. Interestingly, we are able to formulate a first law of thermodynamics for the system as a whole, despite the fact that it is not a stationary blackfold. In particular, the global temperature is given by the rest frame temperature times the gamma factor of special relativity which is the inverse transformation compared to the case of stationary blackfolds. In addition we define two new kinds of thermodynamic conjugate variables, the energy flux W and the integrated velocity on the brane. We find that a phase transition occurs by varying the energy flux W. Below a critical value of W the brane separation ∆ changes only slightly with W. Instead above the critical value ∆ grows exponentially.
In this paper we explore the correspondence between four-dimensional Born-Infeld theory and five-... more In this paper we explore the correspondence between four-dimensional Born-Infeld theory and five-dimensional classical gravity. The Born-Infeld theory side corresponds to the low energy effective theory for open strings ending on coincident D3-branes in a (slowly varying) background Kalb-Ramond field, including all higher-derivative corrections. On the gravity side one has the gravitational (closed string) description of D3-branes in the same background Kalb-Ramond field and the correspondence is thus a consequence of the open/closed string duality. According to the correspondence the gravity side provides a description of the strong coupling limit of Born-Infeld theory. This is a correspondence between effective theories in a similar sense as in the fluid/gravity correspondence. We match the Born-Infeld and gravity sides up to, and including, two-derivative corrections. To this end, we find a new gravity solution for D3-branes with flat embedding in the background of an arbitrary constant background Kalb-Ramond field and show that there are no two-derivative corrections to this for a slowly varying Kalb-Ramond field.
We calculate planar, tree-level, non-extremal three-point functions of operators belonging to the... more We calculate planar, tree-level, non-extremal three-point functions of operators belonging to the SU (2) × SU (2) sector of ABJM theory. First, we generalize the determinant representation, found by Foda for the three-point functions of the SU (2) sector of N = 4 SYM, to the present case and find that, up to normalization factors, the ABJM result factorizes into a product of two N = 4 SYM correlation functions. Secondly, we treat the case where two operators are heavy and one is light and BPS, using a coherent state description of the heavy ones. We show that when normalized by the three-point function of three BPS operators the heavy-heavy-light correlation function agrees, in the Frolov-Tseytlin limit, with its string theory counterpart which we calculate holographically.
The effect of certain simple backgrounds on the Hagedorn temperature in theories of closed string... more The effect of certain simple backgrounds on the Hagedorn temperature in theories of closed strings is examined. The background of interest are a constant Neveu-Schwarz B-field, a constant offset of the space-time metric and a compactified spatial dimension. We find that the Hagedorn temperature of string theory depends on the parameters of the background. We comment on an interesting non-extensive feature of the Hagedorn transition, including a subtlety with decoupling of closed strings in the NCOS limit of open string theory and on the large radius limit of discrete light-cone quantized closed strings.
We investigate the one-loop energy shift δE to certain two-impurity string states in light-cone s... more We investigate the one-loop energy shift δE to certain two-impurity string states in light-cone string field theory on a plane wave background. We find that there exist logarithmic divergences in the sums over intermediate mode numbers which cancel between the cubic Hamiltonian and quartic "contact term". Analyzing the impurity non-conserving channel we find that the non-perturbative O(g 2 2 √ λ ′) contribution to δE/µ predicted in [33] is in fact an artifact of these logarithmic divergences and vanishes with them, leaving an O(g 2 2 λ ′) contribution. Exploiting the supersymmetry algebra, we present a form for the energy shift which appears to be manifestly convergent and free of non-perturbative terms. We use this form to argue that δE/µ receives O(g 2 2 λ ′) contributions at every order in intermediate state impurities.
We compute, on the disk, the non-linear tachyon β-function, β T , of the open bosonic string theo... more We compute, on the disk, the non-linear tachyon β-function, β T , of the open bosonic string theory. β T is determined both in an expansion to the third power of the field and to all orders in derivatives and in an expansion to any power of the tachyon field in the leading order in derivatives. We construct the Witten-Shatashvili (WS) space-time effective action S and prove that it has a very simple universal form in terms of the renormalized tachyon field and β T. The expression for S is well suited to studying both processes that are far off-shell, such as tachyon condensation, and close to the mass-shell, such as perturbative on-shell amplitudes. We evaluate S in a small derivative expansion, providing the exact tachyon potential. The normalization of S is fixed by requiring that the field redefinition that maps S into the tachyon effective action derived from the cubic string field theory is regular on-shell. The normalization factor is in precise agreement with the one required for verifying all the conjectures on tachyon condensation. The coordinates in the space of couplings in which the tachyon β-function is non linear are the most appropriate to study RG fixed points that can be interpreted as solitons of S, i.e. D-branes.
The thermodynamics of type IIB superstring theory in the maximally supersymmetric plane wave back... more The thermodynamics of type IIB superstring theory in the maximally supersymmetric plane wave background is studied. We compute the thermodynamic partition function for non-interacting strings exactly and the result differs slightly from previous computations. We clarify some of the issues related to the Hagedorn temperature in the limits of small and large constant RR 5-form. We study the thermodynamic behavior of strings in the case of AdS 3 × S 3 × T 4 geometries in the presence of NS-NS and RR 3-form backgrounds. We also comment on the relationship of string thermodynamics and the thermodynamic behavior of the sector of Yang-Mills theory which is the holographic dual of the string theory.
Using an effective vertex method we explicitly derive the two-loop dilatation generator of ABJM t... more Using an effective vertex method we explicitly derive the two-loop dilatation generator of ABJM theory in its SU (2)×SU (2) sector, including all non-planar corrections. Subsequently, we apply this generator to a series of finite length operators as well as to two different types of BMN operators. As in N = 4 SYM, at the planar level the finite length operators are found to exhibit a degeneracy between certain pairs of operators with opposite parity-a degeneracy which can be attributed to the existence of an extra conserved charge and thus to the integrability of the planar theory. When non-planar corrections are taken into account the degeneracies between parity pairs disappear hinting the absence of higher conserved charges. The analysis of the BMN operators resembles that of N = 4 SYM. Additional non-planar terms appear for BMN operators of finite length but once the strict BMN limit is taken these terms disappear.
In this paper we assess the performances of different analytical prescriptions for the effective-... more In this paper we assess the performances of different analytical prescriptions for the effective-onebody (EOB) radiation reaction along generic planar orbits using exact numerical result in the testmass limit. We consider three prescriptions put forward in the recent literature: (i) the quasicircular prescription (QC), (ii) the QC with second post-Newtonian (2PN) order noncircular corrections (QC2PN), and (iii) the QC corrected by the noncircular Newtonian prefactor (NCN). The analytical fluxes are then compared against the exact fluxes that are computed by solving the Teukolsky equation with a test-mass source in geodesic motion. We find that the NCN prescription is the most accurate for both eccentric and hyperbolic orbits and it is in robust agreement also for large values of the eccentricity. This result carries over to the comparable masses, as we discuss for a numericalrelativity (NR) case study. We also demonstrate that, while the EOB/NR waveform unfaithfulness is a necessary check for the precision of EOB models, the direct comparison of EOB/NR fluxes is a more stringent and informative test to select the best prescription. Finally, we propose an improved radiation reaction, NCN2PN, that includes noncircular 2PN corrections, in resummed form, as a further multiplicative contribution and that is valid for any mass ratio.
We propose a new approach to find magnetically-dominated force-free magnetospheres around highly ... more We propose a new approach to find magnetically-dominated force-free magnetospheres around highly spinning black holes, relevant for models of astrophysical jets. Employing the near-horizon extreme Kerr (NHEK) limit of the Kerr black hole, any stationary, axisymmetric and regular forcefree magnetosphere reduces to the same attractor solution in the NHEK limit with null electromagnetic field strength. We use this attractor solution as the universal starting point for perturbing away from the NHEK region in the extreme Kerr spacetime. We demonstrate that by going to second order in perturbation theory, it is possible to find magnetically dominated magnetospheres around the extreme Kerr black hole. Furthermore, we consider the near-horizon near-extreme Kerr (near-NHEK) limit that provides access to a different regime of highly spinning black holes. Also in this case we find a novel force-free attractor, which can be used as the universal starting point for a perturbative construction of force-free magnetospheres. Finally, we discuss the relation between the NHEK and near-NHEK attractors.
We study the discrete light-cone quantization (DLCQ) of closed strings in the background of Minko... more We study the discrete light-cone quantization (DLCQ) of closed strings in the background of Minkowski space-time and a constant Neveu-Schwarz B-field. For the Bosonic string, we identify the B-dependent part of the thermodynamic free energy to all orders in string perturbation theory. For every genus, B appears in a constraint in the path integral which restricts the world-sheet geometries to those which are branched covers of a certain torus. This is the extension of a previous result where the B-field was absent [1]. We then discuss the coupling of a B-field to the Matrix model of Mtheory. We show that, when we consider this theory at finite temperature and in a finite B-field, the Matrix variables are functions which live on a torus with the same Teichmüller parameter as the one that we identified in string theory. We show explicitly that the thermodynamic partition function of the Matrix string model in the limit of free strings reproduces the genus 1 thermodynamic partition function of type IIA string. This is strong evidence that the Matrix model can reproduce perturbative string theory. We also find an interesting behavior of the Hagedorn temperature.
General relativity (GR) will be imminently challenged by upcoming experiments in the strong gravi... more General relativity (GR) will be imminently challenged by upcoming experiments in the strong gravity regime, including those testing the energy extraction mechanisms for black holes. Motivated by this, we explore magnetospheric models and black hole jet emissions in Modified Gravity (MOG) scenarios. Specifically, we construct new power emitting magnetospheres in a Kerr-MOG background which are found to depend non-trivially on the MOG deformation parameter. This may allow for high-precision tests of GR. In addition, a complete set of analytic solutions for vacuum magnetic field configurations around static MOG black holes are explicitly derived, and found to comprise exclusively Heun's polynomials.
Journal of Cosmology and Astroparticle Physics, Oct 22, 2020
We consider force-free magnetospheres around the extreme Kerr black hole. In this case there is n... more We consider force-free magnetospheres around the extreme Kerr black hole. In this case there is no known exact analytic solution to force free electrodynamics which is stationary, axisymmetric and magnetically-dominated. However, any stationary, axisymmetric and regular force-free magnetosphere in extreme Kerr black hole approaches the same attractor solution in the near-horizon extreme Kerr (NHEK) limit with null electromagnetic field. We show that by moving away from the attractor solution in the NHEK region, one finds magnetically-dominated solutions in the extreme Kerr black hole with finite angular momentum outflow. This result is achieved using a perturbative analysis up to the second order.
We analyse the formation and evolution of the event horizon of a black hole binary merger when th... more We analyse the formation and evolution of the event horizon of a black hole binary merger when the black holes are charged. We find that the presence of charge influences the properties of the merger and can be useful for investigating the validity of various theories of modified gravity and several proposals for dark matter candidates. It can moreover give insights into various aspects of astrophysical phenomena involving black holes, such as degeneracies in the gravitational wave parameter determination. We perform our analysis both analytically and numerically, in D = 4 dimensions, in the Extreme Mass Ratio (EMR) limit and compare the results. The development of analytical results in the EMR limit is of uttermost importance in view of the upcoming observations of the LISA interferometer. We then use our analysis to describe how the horizon evolves in time during the merger and to investigate the growth in the area of the event horizon and the duration of the merger. We moreover provide a numerical solution valid in arbitrary dimensions D ≥ 4 which could be of interest in the context of the AdS/CFT correspondence or for examining possible extensions of general relativity.
We provide the post-Newtonian (PN) waveform for binary systems in motion along generic planar orb... more We provide the post-Newtonian (PN) waveform for binary systems in motion along generic planar orbits at 2.5PN accuracy, in terms of the dynamical variables of the effective one-body (EOB) formalism. In addition to the calculation of the higher order terms for all the contributions to the waveform that have been already considered in previous avatars of EOB models, we also compute the EOB expression of the oscillatory memory terms. These are purely non-circular contributions, first appearing at 1.5PN order, that have been so far neglected in the EOB literature. This should foster their inclusion in EOB models and the definitive assessment of their role in shaping gravitational wave signals at infinity. To further promote the application of our results, we also derive associated non-circular factors according to the waveform factorization prescription of the non-circular EOB model TEOBResumS-DALI; the result is a set of ready-to-use non-circular factors that can be directly implemented as extra non-circular corrections in the waveform of TEOBResumS-DALI. 1 We recall in this respect that the PN expansion is essentially an expansion for small internal velocities of the considered system, and it is usually organized in powers of 1/c, with c being the speed of light. In particular, terms proportional to 1/c n correspond to corrections at n 2 PN order.
We present a new approach to factorize and resum the post-Newtonian (PN) waveform for generic equ... more We present a new approach to factorize and resum the post-Newtonian (PN) waveform for generic equatorial motion to be used within effective-one-body (EOB) based waveform models. The new multipolar waveform factorization improves previous prescriptions in that: (i) the generic Newtonian contribution is factored out from each multipole; (ii) the circular part is factored out and resummed using standard EOB methods and (iii) the residual, 2PN-accurate, noncircular part, and in particular the tail contribution, is additionally resummed using Padé approximants. The resulting waveform is validated in the extreme-mass-ratio limit by comparisons with nine (mostly nonspinning) numerical waveforms either from eccentric inspirals, with eccentricities up to e = 0.9, or dynamical captures. The resummation of the noncircular tail contribution is found essential to obtain excellent (0.05 rad at periastron for e = 0.9) analytical/numerical agreement and to considerably improve the prescription with just the Newtonian prefactor. In the comparable mass case, the new 2PN waveform shows only a marginal improvement over the previous Newtonian factorization, though yielding maximal unfaithfulness 10 −3 with the 28 publicly available numerical relativity simulations with eccentricity up to ∼ 0.3 (except for a single outlier that grazes 10 −2). We finally use test-particle data to validate the waveform factorization proposed by Khalil et al. [Phys. Rev. 104 (2021) 2, 024046] and conclude that its amplitude can be considered reliable (though less accurate, ∼ 6% fractional difference versus 1.5% of our method) only up to eccentricities ∼ 0.3.
We obtain a first order post-Minkowskian two-body effective potential whose post-Newtonian expans... more We obtain a first order post-Minkowskian two-body effective potential whose post-Newtonian expansion directly reproduces the Einstein-Infeld-Hoffmann potential. Post-Minkowskian potentials can be extracted from on-shell scattering amplitudes in a quantum field theory of scalar matter coupled to gravity. Previously, such potentials did not reproduce the Einstein-Infeld-Hoffmann potential without employing a suitable canonical transformation. In this work, we resolve this issue by obtaining a new expression for the first-order post-Minkowskian potential. This is accomplished by exploiting the reference frame dependence that arises in the scattering amplitude computation. Finally, as a check on our result, we demonstrate that our new potential gives the correct scattering angle.
In this paper we use the effective blackfold description of branes to extend the study of the the... more In this paper we use the effective blackfold description of branes to extend the study of the thermal BIon, a D-brane and parallel anti-D-brane connected by a wormhole with F-string charge in hot flat space, by introducing a radial boost along the brane. The boosted system behaves qualitatively differently from both the extremal and the thermal BIon considered previously. Interestingly, we are able to formulate a first law of thermodynamics for the system as a whole, despite the fact that it is not a stationary blackfold. In particular, the global temperature is given by the rest frame temperature times the gamma factor of special relativity which is the inverse transformation compared to the case of stationary blackfolds. In addition we define two new kinds of thermodynamic conjugate variables, the energy flux W and the integrated velocity on the brane. We find that a phase transition occurs by varying the energy flux W. Below a critical value of W the brane separation ∆ changes only slightly with W. Instead above the critical value ∆ grows exponentially.
In this paper we explore the correspondence between four-dimensional Born-Infeld theory and five-... more In this paper we explore the correspondence between four-dimensional Born-Infeld theory and five-dimensional classical gravity. The Born-Infeld theory side corresponds to the low energy effective theory for open strings ending on coincident D3-branes in a (slowly varying) background Kalb-Ramond field, including all higher-derivative corrections. On the gravity side one has the gravitational (closed string) description of D3-branes in the same background Kalb-Ramond field and the correspondence is thus a consequence of the open/closed string duality. According to the correspondence the gravity side provides a description of the strong coupling limit of Born-Infeld theory. This is a correspondence between effective theories in a similar sense as in the fluid/gravity correspondence. We match the Born-Infeld and gravity sides up to, and including, two-derivative corrections. To this end, we find a new gravity solution for D3-branes with flat embedding in the background of an arbitrary constant background Kalb-Ramond field and show that there are no two-derivative corrections to this for a slowly varying Kalb-Ramond field.
We calculate planar, tree-level, non-extremal three-point functions of operators belonging to the... more We calculate planar, tree-level, non-extremal three-point functions of operators belonging to the SU (2) × SU (2) sector of ABJM theory. First, we generalize the determinant representation, found by Foda for the three-point functions of the SU (2) sector of N = 4 SYM, to the present case and find that, up to normalization factors, the ABJM result factorizes into a product of two N = 4 SYM correlation functions. Secondly, we treat the case where two operators are heavy and one is light and BPS, using a coherent state description of the heavy ones. We show that when normalized by the three-point function of three BPS operators the heavy-heavy-light correlation function agrees, in the Frolov-Tseytlin limit, with its string theory counterpart which we calculate holographically.
The effect of certain simple backgrounds on the Hagedorn temperature in theories of closed string... more The effect of certain simple backgrounds on the Hagedorn temperature in theories of closed strings is examined. The background of interest are a constant Neveu-Schwarz B-field, a constant offset of the space-time metric and a compactified spatial dimension. We find that the Hagedorn temperature of string theory depends on the parameters of the background. We comment on an interesting non-extensive feature of the Hagedorn transition, including a subtlety with decoupling of closed strings in the NCOS limit of open string theory and on the large radius limit of discrete light-cone quantized closed strings.
We investigate the one-loop energy shift δE to certain two-impurity string states in light-cone s... more We investigate the one-loop energy shift δE to certain two-impurity string states in light-cone string field theory on a plane wave background. We find that there exist logarithmic divergences in the sums over intermediate mode numbers which cancel between the cubic Hamiltonian and quartic "contact term". Analyzing the impurity non-conserving channel we find that the non-perturbative O(g 2 2 √ λ ′) contribution to δE/µ predicted in [33] is in fact an artifact of these logarithmic divergences and vanishes with them, leaving an O(g 2 2 λ ′) contribution. Exploiting the supersymmetry algebra, we present a form for the energy shift which appears to be manifestly convergent and free of non-perturbative terms. We use this form to argue that δE/µ receives O(g 2 2 λ ′) contributions at every order in intermediate state impurities.
We compute, on the disk, the non-linear tachyon β-function, β T , of the open bosonic string theo... more We compute, on the disk, the non-linear tachyon β-function, β T , of the open bosonic string theory. β T is determined both in an expansion to the third power of the field and to all orders in derivatives and in an expansion to any power of the tachyon field in the leading order in derivatives. We construct the Witten-Shatashvili (WS) space-time effective action S and prove that it has a very simple universal form in terms of the renormalized tachyon field and β T. The expression for S is well suited to studying both processes that are far off-shell, such as tachyon condensation, and close to the mass-shell, such as perturbative on-shell amplitudes. We evaluate S in a small derivative expansion, providing the exact tachyon potential. The normalization of S is fixed by requiring that the field redefinition that maps S into the tachyon effective action derived from the cubic string field theory is regular on-shell. The normalization factor is in precise agreement with the one required for verifying all the conjectures on tachyon condensation. The coordinates in the space of couplings in which the tachyon β-function is non linear are the most appropriate to study RG fixed points that can be interpreted as solitons of S, i.e. D-branes.
The thermodynamics of type IIB superstring theory in the maximally supersymmetric plane wave back... more The thermodynamics of type IIB superstring theory in the maximally supersymmetric plane wave background is studied. We compute the thermodynamic partition function for non-interacting strings exactly and the result differs slightly from previous computations. We clarify some of the issues related to the Hagedorn temperature in the limits of small and large constant RR 5-form. We study the thermodynamic behavior of strings in the case of AdS 3 × S 3 × T 4 geometries in the presence of NS-NS and RR 3-form backgrounds. We also comment on the relationship of string thermodynamics and the thermodynamic behavior of the sector of Yang-Mills theory which is the holographic dual of the string theory.
Using an effective vertex method we explicitly derive the two-loop dilatation generator of ABJM t... more Using an effective vertex method we explicitly derive the two-loop dilatation generator of ABJM theory in its SU (2)×SU (2) sector, including all non-planar corrections. Subsequently, we apply this generator to a series of finite length operators as well as to two different types of BMN operators. As in N = 4 SYM, at the planar level the finite length operators are found to exhibit a degeneracy between certain pairs of operators with opposite parity-a degeneracy which can be attributed to the existence of an extra conserved charge and thus to the integrability of the planar theory. When non-planar corrections are taken into account the degeneracies between parity pairs disappear hinting the absence of higher conserved charges. The analysis of the BMN operators resembles that of N = 4 SYM. Additional non-planar terms appear for BMN operators of finite length but once the strict BMN limit is taken these terms disappear.
In this paper we assess the performances of different analytical prescriptions for the effective-... more In this paper we assess the performances of different analytical prescriptions for the effective-onebody (EOB) radiation reaction along generic planar orbits using exact numerical result in the testmass limit. We consider three prescriptions put forward in the recent literature: (i) the quasicircular prescription (QC), (ii) the QC with second post-Newtonian (2PN) order noncircular corrections (QC2PN), and (iii) the QC corrected by the noncircular Newtonian prefactor (NCN). The analytical fluxes are then compared against the exact fluxes that are computed by solving the Teukolsky equation with a test-mass source in geodesic motion. We find that the NCN prescription is the most accurate for both eccentric and hyperbolic orbits and it is in robust agreement also for large values of the eccentricity. This result carries over to the comparable masses, as we discuss for a numericalrelativity (NR) case study. We also demonstrate that, while the EOB/NR waveform unfaithfulness is a necessary check for the precision of EOB models, the direct comparison of EOB/NR fluxes is a more stringent and informative test to select the best prescription. Finally, we propose an improved radiation reaction, NCN2PN, that includes noncircular 2PN corrections, in resummed form, as a further multiplicative contribution and that is valid for any mass ratio.
We propose a new approach to find magnetically-dominated force-free magnetospheres around highly ... more We propose a new approach to find magnetically-dominated force-free magnetospheres around highly spinning black holes, relevant for models of astrophysical jets. Employing the near-horizon extreme Kerr (NHEK) limit of the Kerr black hole, any stationary, axisymmetric and regular forcefree magnetosphere reduces to the same attractor solution in the NHEK limit with null electromagnetic field strength. We use this attractor solution as the universal starting point for perturbing away from the NHEK region in the extreme Kerr spacetime. We demonstrate that by going to second order in perturbation theory, it is possible to find magnetically dominated magnetospheres around the extreme Kerr black hole. Furthermore, we consider the near-horizon near-extreme Kerr (near-NHEK) limit that provides access to a different regime of highly spinning black holes. Also in this case we find a novel force-free attractor, which can be used as the universal starting point for a perturbative construction of force-free magnetospheres. Finally, we discuss the relation between the NHEK and near-NHEK attractors.
We study the discrete light-cone quantization (DLCQ) of closed strings in the background of Minko... more We study the discrete light-cone quantization (DLCQ) of closed strings in the background of Minkowski space-time and a constant Neveu-Schwarz B-field. For the Bosonic string, we identify the B-dependent part of the thermodynamic free energy to all orders in string perturbation theory. For every genus, B appears in a constraint in the path integral which restricts the world-sheet geometries to those which are branched covers of a certain torus. This is the extension of a previous result where the B-field was absent [1]. We then discuss the coupling of a B-field to the Matrix model of Mtheory. We show that, when we consider this theory at finite temperature and in a finite B-field, the Matrix variables are functions which live on a torus with the same Teichmüller parameter as the one that we identified in string theory. We show explicitly that the thermodynamic partition function of the Matrix string model in the limit of free strings reproduces the genus 1 thermodynamic partition function of type IIA string. This is strong evidence that the Matrix model can reproduce perturbative string theory. We also find an interesting behavior of the Hagedorn temperature.
General relativity (GR) will be imminently challenged by upcoming experiments in the strong gravi... more General relativity (GR) will be imminently challenged by upcoming experiments in the strong gravity regime, including those testing the energy extraction mechanisms for black holes. Motivated by this, we explore magnetospheric models and black hole jet emissions in Modified Gravity (MOG) scenarios. Specifically, we construct new power emitting magnetospheres in a Kerr-MOG background which are found to depend non-trivially on the MOG deformation parameter. This may allow for high-precision tests of GR. In addition, a complete set of analytic solutions for vacuum magnetic field configurations around static MOG black holes are explicitly derived, and found to comprise exclusively Heun's polynomials.
Journal of Cosmology and Astroparticle Physics, Oct 22, 2020
We consider force-free magnetospheres around the extreme Kerr black hole. In this case there is n... more We consider force-free magnetospheres around the extreme Kerr black hole. In this case there is no known exact analytic solution to force free electrodynamics which is stationary, axisymmetric and magnetically-dominated. However, any stationary, axisymmetric and regular force-free magnetosphere in extreme Kerr black hole approaches the same attractor solution in the near-horizon extreme Kerr (NHEK) limit with null electromagnetic field. We show that by moving away from the attractor solution in the NHEK region, one finds magnetically-dominated solutions in the extreme Kerr black hole with finite angular momentum outflow. This result is achieved using a perturbative analysis up to the second order.
Uploads
Papers by Marta Orselli