DOCSLIB.ORG

Theory of Cyclotron Superradiance from a Moving Electron Bunch Under Group Synchronism Conditions N

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Theory of Cyclotron Superradiance from a Moving Electron Bunch Under Group Synchronism Conditions N Technical Physics, Vol. 45, No. 7, 2000, pp. 813–820. Translated from Zhurnal Tekhnicheskoœ Fiziki, Vol. 70, No. 7, 2000, pp. 1–8. Original Russian Text Copyright © 2000 by Ginzburg, Zotova, Sergeev. THEORETICAL AND MATHEMATICAL PHYSICS Theory of Cyclotron Superradiance from a Moving Electron Bunch under Group Synchronism Conditions N. S. Ginzburg, I. V. Zotova, and A. S. Sergeev Institute of Applied Physics, Russian Academy of Sciences, ul. Ul’yanova 46, Nizhni Novgorod, 603600 Russia Received August 5, 1999 Abstract—A theory is presented of cyclotron superradiance from an electron bunch rotating in a uniform mag- netic field and drifting at a velocity close to the group velocity of a wave propagating in a waveguide. It is shown that, in a comoving frame of reference, the bunch emits radiation at a frequency close to the cutoff frequency of the waveguide. Superradiance implies the azimuthal self-bunching of electrons, which is accompanied by coherent emission of the stored rotational energy in a short electromagnetic pulse. Linear and nonlinear stages of the process are analyzed. The growth rate of the superradiance instability is determined. It is shown that the maximum growth rate is attained under group synchronism conditions. The peak power and the characteristic duration of the cyclotron superradiance pulse are determined by numerical simulation. The characteristic fea- tures of the superradiance pulses are described in the comoving and laboratory frames. The results of theoretical analysis are compared with experimental data. © 2000 MAIK “Nauka/Interperiodica”. INTRODUCTION electron bunch is close to the group velocity of the elec- tromagnetic wave: Induced emission from a spatially localized electron ≈ ensemble (bunch) whose size significantly exceeds the V || V gr. (1) emission wavelength but is much smaller than the inter- action scale length is one of the promising methods for The low rate at which the energy outflows from the generating ultrashort electromagnetic pulses. Emission electron resonator formed by the electron bunch allows from such a bunch can be considered a classical analog the maximum growth rate of the SR instability [16, 19]. of a quantum effect known as Dicke superradiance Condition (1) can be met, e.g., when the radiation [1−3], which is the emission of an electromagnetic propagates in a waveguide; in this case, the dispersion pulse with a duration shorter than the relaxation time of curves of the wave and of the electron flux are tangent the emitting atomic ensemble with population inver- (Fig. 1a).1 Note that, in the comoving frame, in which sion. In classical electrodynamics, superradiance (SR) the bunch as a whole is at rest, the regime of group syn- can be attributed to various mechanisms for induced chronism corresponds to the emission of radiation at a emission [4–21]; in particular, SR can be produced by frequency close to the cutoff frequency and, therefore, an electron bunch rotating in a uniform magnetic field exhibits several advantages typical of electron–wave (cyclotron SR) [10–22]. interaction in gyrotrons, in which the operating mode is Cyclotron SR implies the azimuthal self-bunching also excited at the quasi-cutoff frequency [22]. In par- of electrons, which is accompanied by coherent emis- ticular, SR at the quasi-cutoff frequency is less sensitive sion of the stored rotational energy. The phase self- to the scatter in the electron bunch parameters, includ- locking is related to the relativistic dependence of the ing the longitudinal bunch spreading caused by both gyrofrequency on the particle energy [23] and is similar Coulomb repulsion and the spread in the initial electron to that occurring in cyclotron resonance masers (CRM). velocities. However, in CRMs, quasi-continuous electron beams Earlier, we reported on the first experimental obser- are used; i.e., the electrons that leave the interaction vations of cyclotron SR in the millimeter wavelength region are replaced by the electrons continuously range [20, 21]. In those experiments, we used electron injected from the cathode, thus providing the condi- bunches with a length of 5–7 cm, particle energy of up tions for steady-state generation. In contrast, SR is to 200–250 keV, and current of about 200–500 A. The pulsed in character and can be realized when each par- electron bunches propagated in a 30-cm smooth cylin- ticle stays in a moving or resting electron bunch for a drical waveguide placed in a uniform magnetic field. long time (ideally, for an infinitely long time). This fact We observed the generation of ultrashort (up to 400 ps) also accounts for the absence of an SR threshold [18]. electromagnetic pulses with the peak power higher than Earlier, we showed [19] that the regime of group 1 Group synchronism condition (1) can also be met in the case synchronism is the most favorable for the observation when an electron bunch propagates in a dispersive medium, e.g., of cyclotron SR. In this regime, the drift velocity of the in a homogeneous plasma. 1063-7842/00/4507-0813 $20.00 © 2000 MAIK “Nauka/Interperiodica” 814 GINZBURG et al. ω ω' waveguide modes, yields the following expression for (a) (b) the transverse component of the magnetic field:2 V || V ||V ' γ [ , ] γ ph H⊥ = ||H⊥ – ----- z0 E⊥ = ||H⊥1 – ------------- 0. c c2 Therefore, the regime of group synchronism in the ω c ω ω laboratory frame (the dispersion curves are tangent) ω H' = c H corresponds to the emission of radiation at a quasi-cut- off frequency in the comoving frame (Fig. 1b). h h' Thus, in the K ' frame, the bunch electrons rotate in the magnetic field but the bunch as a whole is at rest. Fig. 1. Dispersion curves corresponding to the regime of The linear size of the bunch in the z' direction is b' = group synchronism in (a) laboratory frame and (b) comov- γ ± b ||0. The bunch radiates isotropically in the z' direc- ing frame. tions. Assuming that the transverse field structure of the emitted radiation coincides with that of one of the 200 kW. SR pulses were recorded only under condi- waveguide modes E⊥(r⊥), we represent the radiation tions close to the condition of group synchronism with field in the form various waveguide modes. Far from group synchro- E' = Re[E⊥(r⊥)A'(z', t')exp(iω t')], (2) nism, the generation of SR pulses was absent. Thus, the c ω experimental results proved that the regime of group where c is the carrier frequency coinciding with the synchronism is optimum for SR. cutoff frequency of the operating mode. According to This paper is devoted to a theoretical study of cyclo- the dispersion relations, the evolution of the axial field tron SR in the regime of group synchronism. A'(x', t') distribution is described by the inhomogeneous parabolic equation ∂2a ∂a 1. CYCLOTRON SUPERRADIANCE i--------- + ------ = 2if (Z')GJ. (3) IN THE COMOVING FRAME ∂Z'2 ∂τ' 1.1. Basic Equations 2π π βˆ Θ The transverse electric current J = 1/ ∫ +d 0 Let a planar bunch of cyclotron oscillators of length b 0 move in a cylindrical waveguide at a longitudinal exciting the electromagnetic field can be found from velocity close to the group velocity of an electromag- the equations of electron motion. Assuming that the netic wave, so that condition (1) is satisfied. In the lab- ! oratory frame, the dispersion curve of the electromag- transverse electron velocity is nonrelativistic (V ⊥' c), –1 ω2 ω 2 1/2 these equations can be represented in the form of equa- netic wave (h = c ( – c ) ) and of the electron flux tions for nonisochronous oscillators, which are well- ω ω ω ( – hV|| = H) are tangent (Fig. 1a). Here, c is the known in the CRM theory: ω γ waveguide cutoff frequency and H = eH0/mc is the 2 relativistic gyrofrequency. ∂βˆ + -------- + iβˆ +( βˆ + – ∆ – 1) = ia. (4) We consider the emission from the electron bunch in ∂τ' the comoving frame K', in which the bunch as a whole Equation (4) describes azimuthal self-bunching of is at rest. The Lorentz transformation for the longitudi- electrons caused by the dependence of the gyrofre- nal wave number h' is quency on the electron energy. In Eqs. (3) and (4), we ω use the following dimensionless variables: the γ V || γ V || h' = ||h – --------- = ||h1 – ------------ , βˆ c2 V c2 normalized transverse electron velocity + = ph ω β β β exp(i ct)( ' + i ' )'/ ⊥' ; ω x y 0 where Vph = /h is the phase velocity of the electromag- 2 2 –1/2 3 netic wave and γ|| = (1 – V|| /c ) . a = (2eA'/mcω β⊥' )J (R ω /c), c 0 m – 1 0 c It is well known that, when an electromagnetic wave 2 2 Z' = z'β⊥' ω /c, τ' = t'β⊥' ω /2; propagates in a waveguide, the relationship VgrVph = c 0 c 0 c holds [23]. It is seen from the group synchronism con- dition (1) that the longitudinal wavenumber vanishes in 2 Similar considerations for transverse magnetic (TM) modes show the comoving frame. Similarly, the allowance for the that the transverse component of the electric field vanishes in the comoving frame when condition (1) is satisfied. For this reason, relationship E⊥ = [H⊥, z0]Vph/c (where z0 is a unit vec- the interaction with TM modes is ineffective in the regime of tor), which is valid for transverse electric (TE) group synchronism. TECHNICAL PHYSICS Vol. 45 No. 7 2000 THEORY OF CYCLOTRON SUPERRADIANCE FROM A MOVING ELECTRON BUNCH 815 the detuning of the unperturbed cyclotron frequency where hˆ = (Ω + ∆)1/2 and χ = (Ω + ∆ – 4G(Ω – 1)/Ω2)1/2 from the cutoff frequency (in the comoving frame) ∆ = are the wavenumbers outside and inside the bunch, ω ω ω β 2 respectively.
Load more

Recommended publications
  • Dicke's Superradiance in Astrophysics
    Western University Scholarship@Western Electronic Thesis and Dissertation Repository 9-1-2016 12:00 AM Dicke’s Superradiance in Astrophysics Fereshteh Rajabi The University of Western Ontario Supervisor Prof. Martin Houde The University of Western Ontario Graduate Program in Physics A thesis submitted in partial fulfillment of the equirr ements for the degree in Doctor of Philosophy © Fereshteh Rajabi 2016 Follow this and additional works at: https://ir.lib.uwo.ca/etd Part of the Physical Processes Commons, Quantum Physics Commons, and the Stars, Interstellar Medium and the Galaxy Commons Recommended Citation Rajabi, Fereshteh, "Dicke’s Superradiance in Astrophysics" (2016). Electronic Thesis and Dissertation Repository. 4068. https://ir.lib.uwo.ca/etd/4068 This Dissertation/Thesis is brought to you for free and open access by Scholarship@Western. It has been accepted for inclusion in Electronic Thesis and Dissertation Repository by an authorized administrator of Scholarship@Western. For more information, please contact [email protected]. Abstract It is generally assumed that in the interstellar medium much of the emission emanating from atomic and molecular transitions within a radiating gas happen independently for each atom or molecule, but as was pointed out by R. H. Dicke in a seminal paper several decades ago this assumption does not apply in all conditions. As will be discussed in this thesis, and following Dicke's original analysis, closely packed atoms/molecules can interact with their common electromagnetic field and radiate coherently through an effect he named superra- diance. Superradiance is a cooperative quantum mechanical phenomenon characterized by high intensity, spatially compact, burst-like features taking place over a wide range of time- scales, depending on the size and physical conditions present in the regions harbouring such sources of radiation.
    [Show full text]
  • Schwarzschild Black Hole Can Also Produce Super-Radiation Phenomena
    Schwarzschild black hole can also produce super-radiation phenomena Wen-Xiang Chen∗ Department of Astronomy, School of Physics and Materials Science, GuangZhou University According to traditional theory, the Schwarzschild black hole does not produce super radiation. If the boundary conditions are set in advance, the possibility is combined with the wave function of the coupling of the boson in the Schwarzschild black hole, and the mass of the incident boson acts as a mirror, so even if the Schwarzschild black hole can also produce super-radiation phenomena. Keywords: Schwarzschild black hole, superradiance, Wronskian determinant I. INTRODUCTION In a closely related study in 1962, Roger Penrose proposed a theory that by using point particles, it is possible to extract rotational energy from black holes. The Penrose process describes the fact that the Kerr black hole energy layer region may have negative energy relative to the observer outside the horizon. When a particle falls into the energy layer region, such a process may occur: the particle from the black hole To escape, its energy is greater than the initial state. It can also show that in Reissner-Nordstrom (charged, static) and rotating black holes, a generalized ergoregion and similar energy extraction process is possible. The Penrose process is a process inferred by Roger Penrose that can extract energy from a rotating black hole. Because the rotating energy is at the position of the black hole, not in the event horizon, but in the area called the energy layer in Kerr space-time, where the particles must be like a propelling locomotive, rotating with space-time, so it is possible to extract energy .
    [Show full text]
  • Coherently Amplifying Photon Production from Vacuum with a Dense Cloud of Accelerating Photodetectors ✉ Hui Wang 1 & Miles Blencowe 1
    ARTICLE https://doi.org/10.1038/s42005-021-00622-3 OPEN Coherently amplifying photon production from vacuum with a dense cloud of accelerating photodetectors ✉ Hui Wang 1 & Miles Blencowe 1 An accelerating photodetector is predicted to see photons in the electromagnetic vacuum. However, the extreme accelerations required have prevented the direct experimental ver- ification of this quantum vacuum effect. In this work, we consider many accelerating pho- todetectors that are contained within an electromagnetic cavity. We show that the resulting photon production from the cavity vacuum can be collectively enhanced such as to be 1234567890():,; measurable. The combined cavity-photodetectors system maps onto a parametrically driven Dicke-type model; when the detector number exceeds a certain critical value, the vacuum photon production undergoes a phase transition from a normal phase to an enhanced superradiant-like, inverted lasing phase. Such a model may be realized as a mechanical membrane with a dense concentration of optically active defects undergoing gigahertz flexural motion within a superconducting microwave cavity. We provide estimates suggesting that recent related experimental devices are close to demonstrating this inverted, vacuum photon lasing phase. ✉ 1 Department of Physics and Astronomy, Dartmouth College, Hanover, NH, USA. email: [email protected] COMMUNICATIONS PHYSICS | (2021) 4:128 | https://doi.org/10.1038/s42005-021-00622-3 | www.nature.com/commsphys 1 ARTICLE COMMUNICATIONS PHYSICS | https://doi.org/10.1038/s42005-021-00622-3 ne of the most striking consequences of the interplay Cavity wall Obetween relativity and the uncertainty principle is the predicted detection of real photons from the quantum fi TLS defects electromagnetic eld vacuum by non-inertial, accelerating pho- Cavity mode todetectors.
    [Show full text]
  • Dicke Superradiance in Solids [Invited]
    C80 Vol. 33, No. 7 / July 2016 / Journal of the Optical Society of America B Review Dicke superradiance in solids [Invited] 1 1 2 1 2 KANKAN CONG, QI ZHANG, YONGRUI WANG, G. TIMOTHY NOE II, ALEXEY BELYANIN, AND 1,3,4, JUNICHIRO KONO * 1Department of Electrical and Computer Engineering, Rice University, Houston, Texas 77005, USA 2Department of Physics and Astronomy, Texas A&M University, College Station, Texas 77843, USA 3Department of Physics and Astronomy, Rice University, Houston, Texas 77005, USA 4Department of Materials Science and NanoEngineering, Rice University, Houston, Texas 77005, USA *Corresponding author: [email protected] Received 18 February 2016; revised 7 April 2016; accepted 7 April 2016; posted 8 April 2016 (Doc. ID 259437); published 13 May 2016 Recent advances in optical studies of condensed matter systems have led to the emergence of a variety of phenomena that have conventionally been studied in the realm of quantum optics. These studies have not only deepened our understanding of light–matter interactions but have also introduced aspects of many-body corre- lations inherent in optical processes in condensed matter systems. This paper is concerned with the phenomenon of superradiance (SR), a profound quantum optical process originally predicted by Dicke in 1954. The basic concept of SR applies to a general N body system, where constituent oscillating dipoles couple together through interaction with a common light field and accelerate the radiative decay of the whole system. Hence, the term SR ubiquitously appears in order to describe radiative coupling of an arbitrary number of oscillators in many situations in modern science of both classical and quantum description.
    [Show full text]
  • The Black Hole Bomb and Superradiant Instabilities
    The black hole bomb and superradiant instabilities Vitor Cardoso∗ Centro de F´ısica Computacional, Universidade de Coimbra, P-3004-516 Coimbra, Portugal Oscar´ J. C. Dias† Centro Multidisciplinar de Astrof´ısica - CENTRA, Departamento de F´ısica, F.C.T., Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal Jos´e P. S. Lemos‡ Centro Multidisciplinar de Astrof´ısica - CENTRA, Departamento de F´ısica, Instituto Superior T´ecnico, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal Shijun Yoshida§ Centro Multidisciplinar de Astrof´ısica - CENTRA, Departamento de F´ısica, Instituto Superior T´ecnico, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal ¶ (Dated: February 1, 2008) A wave impinging on a Kerr black hole can be amplified as it scatters off the hole if certain conditions are satisfied giving rise to superradiant scattering. By placing a mirror around the black hole one can make the system unstable. This is the black hole bomb of Press and Teukolsky. We investigate in detail this process and compute the growing timescales and oscillation frequencies as a function of the mirror’s location. It is found that in order for the system black hole plus mirror to become unstable there is a minimum distance at which the mirror must be located. We also give an explicit example showing that such a bomb can be built. In addition, our arguments enable us to justify why large Kerr-AdS black holes are stable and small Kerr-AdS black holes should be unstable. PACS numbers: 04.70.-s I. INTRODUCTION one can extract as much rotational energy as one likes from the black hole.
    [Show full text]
  • A Modern Approach to Superradiance
    A Modern Approach to Superradiance Solomon Endlicha and Riccardo Pencob,c a Stanford Institute for Theoretical Physics, Stanford University, Stanford, CA 94306, USA b Physics Department, Center for Theoretical Physics & Institute for Strings, Cosmology, and Astroparticle Physics, Columbia University, New York, NY 10027, USA c Center for Particle Cosmology, Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA Abstract In this paper, we provide a simple and modern discussion of rotational superradiance based on quantum field theory. We work with an effective theory valid at scales much larger than the size of the spinning object responsible for superradiance. Within this framework, the probability of absorption by an object at rest completely determines the superradiant amplification rate when that same object is spinning. We first discuss in detail superradiant scattering of spin 0 particles with orbital angular momentum ℓ = 1, and then extend our analysis to higher values of orbital angular momentum and spin. Along the way, we provide a simple derivation of vacuum friction—a “quantum torque” acting on spinning objects in empty space. Our results apply not only to black holes but to arbitrary spinning objects. We also discuss superradiant instability due to formation of bound states and, as an illustration, we calculate the instability rate Γ for bound states with massive spin 1 particles. For a black hole with mass M and angular velocity Ω, we find Γ (GMµ)7Ω when the particle’s Compton wavelength 1/µ is ∼ much greater than the size GM of the spinning object. This rate is parametrically much larger than the instability rate for spin 0 particles, which scales like (GMµ)9Ω.
    [Show full text]
  • Super- and Subradiance by Entangled Free Particles
    Super- and subradiance by entangled free particles Aviv Karnieli1,*, Nicholas Rivera2, Ady Arie3 and Ido Kaminer4 1Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Ramat Aviv 69978, Tel Aviv, Israel 2Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA 3School of Electrical Engineering, Fleischman Faculty of Engineering, Tel Aviv University, Tel Aviv 69978, Israel 4Department of Electrical Engineering, Technion–Israel Institute of Technology, Haifa 32000, Israel *corresponding authors: [email protected]; [email protected] When multiple quantum emitters radiate, their emission rate may be enhanced or suppressed due to collective interference in a process known as super- or subradiance. Such processes are well-known to occur also in light emission by free charged particles. To date, all experimental and theoretical studies of super- and subradiance in these systems involved the classical correlations between the emitters. However, dependence on quantum correlations, such as entanglement between different emitting particles, has not been studied. Recent advances in coherent-shaping of free-electron wavefunctions motivate the investigation of such quantum regimes of super- and subradiance. In this Letter, we show how a pair of coincident path-entangled electrons can demonstrate either super- or subradiant light emission, depending on the two-particle wavefunction. By choosing different free-electron Bell-states, the spectrum and emission pattern of the light can be reshaped, in a manner that cannot be accounted for by a classical mixed state. We show these results for light emission in any optical medium, and discuss their generalization to many-body quantum states. Our findings suggest that light emission can be sensitive to the explicit quantum state of the emitting matter wave, and possibly serve as a non-destructive measurement scheme for measuring the quantum state of many-body systems.
    [Show full text]
  • (BEC) with Constant Density
    Analog Black Holes and Energy Extraction by Super-Radiance from Bose Einstein Condensates (BEC) with Constant Density Betül Demirkaya,∗ Tekin Dereli,† Kaan Güven,‡ Department of Physics, Koç University, 34450 Sarıyer, İstanbul, Turkey December 6, 2018 Abstract This paper presents a numerical study of the acoustic superradiance from the single vortex state of a Bose-Einstein condensate (BEC). The draining bathtub model of an incompressible barotropic fluid is adopted to describe the vortex. The propagation of the velocity poten- tial fluctuations are governed by the massless scalar Klein-Gordon wave equation, which establishes the rotating black-hole analogy. Hence, the amplified scattering of these fluctuations from the vortex comprise the superradiance effect. Particular to this study, a coordinate transforma- tion is applied which enables the identification of the event horizon and the ergosphere termwise in the metric. Thus, the respective spectral solutions can be obtained asymptotically at either boundary. Fur- ther, the time-domain calculations of the energy of the propagating perturbations and the independently performed reflection coefficient calculations from the asymptotic solutions of the propagating pertur- bations are shown to be in very good agreement. While the former solution provides the full dynamical behavior of the superradiance, the latter method gives the frequency spectrum of the superradiance as a arXiv:1806.02139v2 [cond-mat.other] 5 Dec 2018 function of the rotational frequency of the vortex. Hence, a compre- hensive analysis of the superradiance effect can be conducted within this workframe. ∗[email protected] †[email protected] ‡[email protected] 1 1 Introduction Analogies in physics enable us to observe a particular phenomenon with the same characteristic features in different systems pertaining to disparate mechanisms and space-time-energy scales.
    [Show full text]
  • Hawking Radiation Is Probably a Type of Superradiation
    Hawking radiation is probably a type of superradiation Yi-Xiao Zhang South China Normal University, Guangzhou 510006,China Wen-Xiang Chen∗ Department of Astronomy, School of Physics and Materials Science, GuangZhou University In this article, it mainly discusses that when the scalar field equation presets boundary condi- tions, the effective action form of Hawking radiation is consistent with the effective action form of superradiation. From this I conclude that Hawking radiation may be a form of superradiation. Keywords: Hawking radiation, superradiance, effective action I. INTRODUCTION Hawking radiation is a kind of thermal radiation emitted by black holes, which is speculated by quantum effect theory. This theory was put forward by physicist Stephen Hawking in 1974. With the Hawking radiation theory, we can explain how to reduce the mass of black holes to cause black hole evapotranspiration. And because Hawking radiation can cause black holes to lose mass, when black holes lose more mass than they increase, they will shrink and eventually disappear. The divergence of a relatively small black hole is usually larger than that of a normal black hole, so the former shrinks and disappears faster than the latter. Hawking's analysis quickly became the first convincing theory of quantum gravity, although the existence of Hawking radiation has not yet been actually observed. In June 2008, NASA launched the GLAST satellite, which can search for flashes of gamma rays in evaporating black holes. In the theory of extra dimensions, collisions of high-energy particles may also create black holes that disappear by themselves. In September 2010, the results of a simulated gravity study were considered by some scientists to demonstrate the possible existence and possible nature of Hawking radiation for the first time.
    [Show full text]
  • On the Effect of Scalar Fields on Hawking Radiation and Quasinormal
    DOCTORAL THESIS On the effect of scalar fields on Hawking radiation and quasinormal modes of black holes By Avijit Chowdhury Roll No.: 13IP001 Department of Physical Sciences Indian Institute of Science Education and Research Kolkata Supervisor: Prof. Narayan Banerjee arXiv:2106.02294v1 [gr-qc] 4 Jun 2021 A thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy in the Department of Physical Sciences at the Indian Institute of Science Education and Research Kolkata May 21, 2021 iii Declaration by the student Date: May 21, 2021 I, Avijit Chowdhury Registration No. 13IP001 dated 25/07/2013, a stu- dent of Department of Physical Sciences of the Integrated PhD Programme of the Indian Institute of Science Education and Research Kolkata (IISER Kolkata), hereby declare that this thesis is my own work and, to the best of my knowledge, it neither contains materials previously published or writ- ten by any other person, nor it has been submitted for any degree/diploma or any other academic award anywhere before. I also declare that all copyrighted material incorporated into this thesis is in compliance with the Indian Copyright (Amendment) Act, 2012 and that I have received written permission from the copyright owners for my use of their work. I hereby grant permission to IISER Kolkata to store the thesis in a database which can be accessed by others. ———————————– Avijit Chowdhury Department of Physical Sciences Indian Institute of Science Education and Research Kolkata Mohanpur 741246, West Bengal, India v Certificate from the Supervisor Date: May 21, 2021 This is to certify that the thesis entitled “On the effect of scalar fields on Hawking radiation and quasinormal modes of black holes” submitted by Avijit Chowdhury Registration No.
    [Show full text]
  • Ultra Light Boson Dark Matter and Event Horizon Telescope Observations of M87*
    Ultra Light Boson Dark Matter and Event Horizon Telescope Observations of M87* 1, 1, Hooman Davoudiasl ∗ and Peter B. Denton y 1Department of Physics, Brookhaven National Laboratory, Upton, NY 11973, USA The initial data from the Event Horizon Telescope (EHT) on M87∗, the supermassive black hole at the center of the M87 galaxy, provide direct observational information on its mass, spin, and accretion disk properties. A combination of the EHT data and other constraints provide evidence 9 that M87∗ has a mass 6:5 10 M and dimensionless spin parameter a∗ > 0:5. These deter- ∼ × 21 j j minations disfavor ultra light bosons of mass µb 10− eV, within the range considered∼ for fuzzy dark matter, invoked to explain dark matter distribution∼ on kpc scales. Future observations of ∼ M87∗ could be expected to strengthen our conclusions. INTRODUCTION its production in the early Universe. These interactions could then result in its detection in a variety of labora- Black holes (BHs) are at the same time simple and tory experiments. Nonetheless, DM has only been ob- mysterious. They are characterized by only a few pa- served through its gravitational effects in astrophysics rameters - mass, spin, and charge - and are considered and cosmology. Therefore, purely gravitational probes purely gravitational objects. Yet their essential character of DM provide the most model-independent approach to is quite enigmatic: they represent a one-way exit (up to constraining its properties. quantum effects [1]) from the causally connected Uni- It turns out that BHs, themselves purely gravitational, verse, and their internal properties are masked by an can provide a unique probe of ultra light DM states event horizon that is the point of no return.
    [Show full text]
  • Superradiant Amplification by Stars and Black Holes
    Superradiant amplification by stars and black holes Vitor Cardoso1,2 , Richard Brito1, Jo˜ao L. Rosa1, 1 CENTRA, Departamento de F´ısica, Instituto Superior T´ecnico – IST, Universidade de Lisboa – UL, Avenida Rovisco Pais 1, 1049 Lisboa, Portugal and 2 Perimeter Institute for Theoretical Physics Waterloo, Ontario N2J 2W9, Canada It has long been known that dissipation is a crucial ingredient in the superradiant amplification of wavepackets off rotating objects. We show that, once appropriate dissipation mechanisms are included, stars are also prone to superradiance and superradiant instabilities. In particular, ultra- light dark matter with small interaction cross section with the star material or self-annihilation can trigger a superradiant instability. On long timescales, the instability strips the star of most of its angular momentum. Whether or not stationary hairy configurations exist, remains to be seen. PACS numbers: 04.70.-s,04.80.-y,12.60.-i,11.10.St I. INTRODUCTION long as dissipation is included [23]. The purpose of this work is to compute explicitly the amplification factors when a toy model for dissipation is used, and to show Rotating bodies with internal degrees of freedom – that, within this toy model, stars are superradiantly- where energy can be dumped into – display superradi- unstable against massive scalar-field fluctuations. ance. This means that the scattering of low-frequency Our results make possible the existence of hairy stars, waves extracts rotational energy away from the body and supported solely by superradiance. For dark matter mod- is used to amplify incoming radiation [1–3]. When the els comprised of light degrees of freedom, our results open object is a black hole, dissipation is intrinsically built the door to constrain the interaction cross section with in the problem under the form of a one-way membrane: ordinary matter or the self-annihilation cross-section.
    [Show full text]