Luca Visinelli | Shanghai Jiao Tong University (original) (raw)

Papers by Luca Visinelli

We derive the requirements that a generic axion-like field has to satisfy in order to play the ro... more We derive the requirements that a generic axion-like field has to satisfy in order to play the role of the inflaton field in the warm inflation scenario. Compared to the parameter space in ordinary Natural Inflation models, we find that the parameter space in our model is enlarged. In particular, we avoid the problem of having an axion decay constant f that relates to the Planck scale, which is instead present in the ordinary Natural Inflation models; in fact, our model can easily accommodate values of the axion decay constant that lie well below the Planck scale.

We extend the duality symmetry between the electric and the magnetic fields to the case in which ... more We extend the duality symmetry between the electric and the magnetic fields to the case in which an additional axion-like term is present, and we derive the set of Maxwell's equations that preserves this symmetry. This new set of equations allows for a gauge symmetry extending the ordinary symmetry in the classical electrodynamics. We obtain explicit solutions for the new set of equations in the absence of external sources, and we discuss the implications of a new internal symmetry between the axion field and the electromagnetic gauge potential.

The subjects of this thesis are the invisible axion and the more general family of axionlike part... more The subjects of this thesis are the invisible axion and the more general family of axionlike particles. The invisible axion is a hypothetical elementary particle and a cold dark matter candidate. I present an improved computation of the constraints on the parameter space of the cold dark matter axion in the standard cosmology, that includes the contributions from anharmonicities in the axion potential and from the decay of axionic strings. In this scenario, I update the value of the mass of the cold dark matter axion, finding the value (67 ± 17)µeV, approximately one order of magnitude larger than previous computations. The effect of nonstandard cosmological scenarios on the parameter space of axion cold dark matter is studied for the first time. In particular, I consider the cases of lowtemperature reheating and kination cosmologies, and I show that the mass of the cold dark matter axion can differ from the value in the standard cosmological scenario by orders of magnitude. Finally, I consider the family of axion-like particles, assuming that these particles serve as the inflaton in the context of warm inflation. I find that the axion energy scale f , which in the standard inflation scenario is of the order of the Planck mass, can be lowered to the much safer Grand Unification Theory scale f ∼ 10 16 GeV. I also constrain the parameter space and the amount of gravitational waves from this model, using results from the Wilkinson Microwave Anisotropy Probe 7-year data.

Within the framework of the interacting fluid formalism, we provide the numerical solution to the... more Within the framework of the interacting fluid formalism, we provide the numerical solution to the Boltzmann equation describing the evolution of an inflaton field coupled to radiation. We study the behavior of the system during the slow-roll regime, in the case in which an additional stochastic source term is included in the set of equations, and we recover the expression for the cosmological perturbations previously obtained in the Warm inflation scenarios.

arXiv: General Relativity and Quantum Cosmology, 2016

Bulk viscosity leads to negative pressure, which is a key ingredient for successful inflation. We... more Bulk viscosity leads to negative pressure, which is a key ingredient for successful inflation. We build an inflationary model where the slow-roll of the inflaton field is driven by a viscous component instead of the flat potential commonly used. Since viscosity does not contribute to the energy density of the Universe, the Hubble rate depends only on the kinetic energy of the inflaton. The power spectrum is almost scale-invariant, with a tilt depending on the slow-roll parameters defined within the model.

arXiv: Cosmology and Nongalactic Astrophysics, 2019

Persisting tensions between high-redshift and low-redshift cosmological observations suggest the ... more Persisting tensions between high-redshift and low-redshift cosmological observations suggest the dark energy sector of the Universe might be more complex than the positive cosmological constant of the Lambda\LambdaLambdaCDM model. Motivated by string theory, wherein symmetry considerations make consistent AdS backgrounds (\textit (i.e.) maximally symmetric spacetimes with a negative cosmological constant) ubiquitous, we explore a scenario where the dark energy sector consists of two components: a negative cosmological constant, with a dark energy component with equation of state wphiw_{\phi}wphi on top. We test the consistency of the model against low-redshift Baryon Acoustic Oscillation and Type Ia Supernovae distance measurements, assessing two alternative choices of distance anchors: the sound horizon at baryon drag determined by the \textit{Planck} collaboration, and the Hubble constant determined by the SH0ES program. We find no evidence for a negative cosmological constant, and mild indicatio...

The Event Horizon Telescope has recently provided the first image of the dark shadow around the s... more The Event Horizon Telescope has recently provided the first image of the dark shadow around the supermassive black hole M87*. The observation of a highly circular shadow provides strong limits on deviations of M87*'s quadrupole moment from the Kerr value. We show that the absence of such a deviation can be used to constrain the physics of extra dimensions of spacetime. Focusing on the Randall-Sundrum AdS5 brane-world scenario, we show that the observation of M87*'s dark shadow sets the limit ℓ < ∼ 170 AU, where ℓ is the AdS5 curvature radius. This limit is among the first quantitative constraints on exotic physics obtained from the extraordinary first ever image of the dark shadow of a black hole.

Yu-Dai Tsai,1, 2, ∗ Youjia Wu,3, † Sunny Vagnozzi,4, ‡ and Luca Visinelli5, 6, § Fermi National A... more Yu-Dai Tsai,1, 2, ∗ Youjia Wu,3, † Sunny Vagnozzi,4, ‡ and Luca Visinelli5, 6, § Fermi National Accelerator Laboratory (Fermilab), Batavia, IL 60510, USA Kavli Institute for Cosmological Physics (KICP), University of Chicago, Chicago, IL 60637, USA Leinweber Center for Theoretical Physics, University of Michigan, Ann Arbor, MI 48109, USA Kavli Institute for Cosmology (KICC), University of Cambridge, Cambridge CB3 0HA, United Kingdom INFN, Laboratori Nazionali di Frascati, C.P. 13, I-100044 Frascati, Italy Tsung-Dao Lee Institute (TDLI), Shanghai Jiao Tong University, 200240 Shanghai, China (Dated: August 20, 2021)

arXiv: High Energy Physics - Phenomenology, 2020

We propose a new way of studying the Higgs potential at extremely high energies. The SM Higgs bos... more We propose a new way of studying the Higgs potential at extremely high energies. The SM Higgs boson, as a light spectator field during inflation in the early Universe, can acquire large field values from its quantum fluctuations which vary among different causal (Hubble) patches. Such a space dependence of the Higgs after the end of inflation leads to space-dependent SM particle masses and hence variable efficiency of reheating, when the inflaton decays to Higgsed SM particles. Inhomogeneous reheating results in (observable) temperature anisotropies. Further, the resulting temperature anisotropy spectrum acquires a significant non-Gaussian component, which is constrained by itPlanck{\it Planck}itPlanck observations of the Cosmic Microwave Background (CMB) and potentially detectable in next-generation experiments. Hence, in principle, observational searches for non-Gaussianity in the CMB can be used to constrain the dynamics of the Higgs boson at very high (inflationary) energies.

The duality relation between the electric and magnetic fields, in the presence of an additional a... more The duality relation between the electric and magnetic fields, in the presence of an additional axion-like field, is considered. We derive the new equations that describe the electrodynamics in this model, and we discuss the implications for the conservation of the electric and magnetic four-currents and for the propagation of waves.

arXiv: High Energy Physics - Phenomenology, 2008

The University of Utah, Physics Dept. 115 S 1400 E, Salt Lake City, UT USA 84112(Dated: October 2... more The University of Utah, Physics Dept. 115 S 1400 E, Salt Lake City, UT USA 84112(Dated: October 22, 2008)We present an expression for the transition probability between Dirac or Majorananeutrino flavors obtained from first principles within quantum field theory. Ourderivation is based on a standard quantum mechanical setup and includes the specificmechanism of neutrinoproduction only in as much as it specifies the initial state. Ourexpression for the transition probability reproduces the usual formula in the planewave limit and shows the correct non-relativistic and ultra-relativistic behaviors. Italso allows a simple understanding of the decoherence of the oscillations and of thequestion of the arrival times of the different neutrino mass eigenstates. We shownumerical examples for the case of two neutrino generations.

Physical Review D, 2022

We present an analytic study of the dispersion relation for an isotropic magnetized plasma intera... more We present an analytic study of the dispersion relation for an isotropic magnetized plasma interacting with axions. We provide a quantitative picture of the electromagnetic plasma oscillations in both the ultrarelativistic and nonrelativistic regimes and considering both non-degenerate and degenerate media, accounting for the dispersion curves as a function of the plasma temperature and the ratio of the plasma phase velocity to the characteristic velocity of particles. We include the modifications on the Landau damping of plasma waves induced by the presence of the axion field, and we comment on the effects of damping on subluminal plasma oscillations.

We derive a new integral equation that allows the calculation of the scattering or annihilation a... more We derive a new integral equation that allows the calculation of the scattering or annihilation amplitude of two particles subjected to two potentials when the corresponding amplitude for one potential only is known. We assume that scattering or annihilation occurs through one of the potentials, while the other potential affects the particle wave functions. Our expression is valid for any choice of the distorting potential and for any particle model. Our technique does not require the expansion of the amplitude into partial waves, and allows the study of models that are generally difficult to solve by means of the Schroedinger equation.

Sunny Vagnozzi, 2, ∗ Luca Visinelli, 4, 5, † Philippe Brax, ‡ Anne-Christine Davis, 1, § and Jere... more Sunny Vagnozzi, 2, ∗ Luca Visinelli, 4, 5, † Philippe Brax, ‡ Anne-Christine Davis, 1, § and Jeremy Sakstein ¶ Kavli Institute for Cosmology (KICC), University of Cambridge, Madingley Road, Cambridge CB3 0HA, United Kingdom∗∗ Institute of Astronomy (IoA), University of Cambridge, Madingley Road, Cambridge CB3 0HA, United Kingdom Istituto Nazionale di Fisica Nucleare (INFN), Laboratori Nazionali di Frascati, C.P. 13, I-100044 Frascati, Italy∗∗ Tsung-Dao Lee Institute (TDLI), Shanghai Jiao Tong University, 200240 Shanghai, China Gravitation Astroparticle Physics Amsterdam (GRAPPA), University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands Institute de Physique Theórique (IPhT), Université Paris-Saclay, CNRS, CEA, F-91191, Gif-sur-Yvette Cedex, France Department of Applied Mathematics and Theoretical Physics (DAMTP), Center for Mathematical Sciences, University of Cambridge, CB3 0WA, United Kingdom Department of Physics & Astronomy, University of Hawai‘i, Watanabe H...

The search for extra dimensions is a challenging endeavor to probe physics beyond the Standard Mo... more The search for extra dimensions is a challenging endeavor to probe physics beyond the Standard Model. The joint detection of gravity waves (GW) and electromagnetic (EM) signals from the merging of a binary system of compact objects like a neutron star (NS) can help constrain the geometry of extra dimensions. In particular, if our observable Universe is a 3+1 hypersurface or brane embedded in a higher 4+1 Anti-de Sitter (AdS$_5$) spacetime, in which gravity is the only field that propagates through the infinite bulk space while any other field is confined on the brane, then GW and EM signals between two points on the brane would in general travel different paths. This would result in a time lag between the detection of GW and EM signals emitted simultaneously from the same source, with the apparent measurement of a "superluminous" GW speed. Assuming the standard Lambda\LambdaLambda-Cold Dark Matter ($\Lambda$CDM) scenario, we set a bound on the AdS$_5$ radius of curvature $\ell \less...

Cosmic Microwave Background (CMB) observations are used to constrain reheating to Standard Model ... more Cosmic Microwave Background (CMB) observations are used to constrain reheating to Standard Model (SM) particles after a period of inflation. As a light spectator field, the SM Higgs boson acquires large field values from its quantum fluctuations during inflation, gives masses to SM particles that vary from one Hubble patch to another, and thereby produces large density fluctuations. We consider both perturbative and resonant decay of the inflaton to SM particles. For the case of perturbative decay from coherent oscillations of the inflaton after high scale inflation, we find strong constraints on the reheat temperature for the inflaton decay into heavy SM particles. For the case of resonant particle production (preheating) to (Higgsed) SM gauge bosons, we find temperature fluctuations larger than observed in the CMB for a range of gauge coupling that includes those found in the SM and conclude that such preheating cannot be the main source of reheating the Universe after inflation.

Classical and Quantum Gravity

Recently, Tsupko et al. have put forward the very interesting proposal to use the shadows of high... more Recently, Tsupko et al. have put forward the very interesting proposal to use the shadows of highredshift supermassive black holes (SMBHs) as standard rulers. This would in principle allow us to probe the expansion history within a redshift range which would otherwise be challenging to access. In this note, we critically examine this proposal, and identify a number of important issues which had been previously overlooked. These include difficulties in obtaining reliable SMBH mass estimates and reaching the required angular resolution, and an insufficient knowledge of the accretion dynamics of high-redshift SMBHs. While these issues currently appear to prevent high-redshift SMBH shadows from being used as robust standard rulers, we hope that our flagging them early will help in making this probe theoretically mature by the time it will be experimentally feasible.

Monthly Notices of the Royal Astronomical Society, 2021

We consider the observational constraints on stupendously large black holes (SLABs) in the mass r... more We consider the observational constraints on stupendously large black holes (SLABs) in the mass range Mgtrsim1011,mathrmModotM \gtrsim 10^{11}\, \mathrm{ M_{\odot}}Mgtrsim1011,mathrmModot. These have attracted little attention hitherto, and we are aware of no published constraints on a SLAB population in the range (1012–$10^{18})\, \mathrm{ M_{\odot}}$. However, there is already evidence for black holes of up to nearly 1011,mathrmModot10^{11}\, \mathrm{ M_{\odot}}1011,mathrmModot in galactic nuclei, so it is conceivable that SLABs exist and they may even have been seeded by primordial black holes. We focus on limits associated with (i) dynamical and lensing effects, (ii) the generation of background radiation through the accretion of gas during the pre-galactic epoch, and (iii) the gamma-ray emission from the annihilation of the halo of weakly interacting massive particles expected to form around each SLAB if these provide the dark matter. Finally, we comment on the constraints on the mass of ultralight bosons from future measurements of the mass and spin...

We derive the requirements that a generic axion-like field has to satisfy in order to play the ro... more We derive the requirements that a generic axion-like field has to satisfy in order to play the role of the inflaton field in the warm inflation scenario. Compared to the parameter space in ordinary Natural Inflation models, we find that the parameter space in our model is enlarged. In particular, we avoid the problem of having an axion decay constant f that relates to the Planck scale, which is instead present in the ordinary Natural Inflation models; in fact, our model can easily accommodate values of the axion decay constant that lie well below the Planck scale.

We extend the duality symmetry between the electric and the magnetic fields to the case in which ... more We extend the duality symmetry between the electric and the magnetic fields to the case in which an additional axion-like term is present, and we derive the set of Maxwell's equations that preserves this symmetry. This new set of equations allows for a gauge symmetry extending the ordinary symmetry in the classical electrodynamics. We obtain explicit solutions for the new set of equations in the absence of external sources, and we discuss the implications of a new internal symmetry between the axion field and the electromagnetic gauge potential.

The subjects of this thesis are the invisible axion and the more general family of axionlike part... more The subjects of this thesis are the invisible axion and the more general family of axionlike particles. The invisible axion is a hypothetical elementary particle and a cold dark matter candidate. I present an improved computation of the constraints on the parameter space of the cold dark matter axion in the standard cosmology, that includes the contributions from anharmonicities in the axion potential and from the decay of axionic strings. In this scenario, I update the value of the mass of the cold dark matter axion, finding the value (67 ± 17)µeV, approximately one order of magnitude larger than previous computations. The effect of nonstandard cosmological scenarios on the parameter space of axion cold dark matter is studied for the first time. In particular, I consider the cases of lowtemperature reheating and kination cosmologies, and I show that the mass of the cold dark matter axion can differ from the value in the standard cosmological scenario by orders of magnitude. Finally, I consider the family of axion-like particles, assuming that these particles serve as the inflaton in the context of warm inflation. I find that the axion energy scale f , which in the standard inflation scenario is of the order of the Planck mass, can be lowered to the much safer Grand Unification Theory scale f ∼ 10 16 GeV. I also constrain the parameter space and the amount of gravitational waves from this model, using results from the Wilkinson Microwave Anisotropy Probe 7-year data.

Within the framework of the interacting fluid formalism, we provide the numerical solution to the... more Within the framework of the interacting fluid formalism, we provide the numerical solution to the Boltzmann equation describing the evolution of an inflaton field coupled to radiation. We study the behavior of the system during the slow-roll regime, in the case in which an additional stochastic source term is included in the set of equations, and we recover the expression for the cosmological perturbations previously obtained in the Warm inflation scenarios.

arXiv: General Relativity and Quantum Cosmology, 2016

Bulk viscosity leads to negative pressure, which is a key ingredient for successful inflation. We... more Bulk viscosity leads to negative pressure, which is a key ingredient for successful inflation. We build an inflationary model where the slow-roll of the inflaton field is driven by a viscous component instead of the flat potential commonly used. Since viscosity does not contribute to the energy density of the Universe, the Hubble rate depends only on the kinetic energy of the inflaton. The power spectrum is almost scale-invariant, with a tilt depending on the slow-roll parameters defined within the model.

arXiv: Cosmology and Nongalactic Astrophysics, 2019

Persisting tensions between high-redshift and low-redshift cosmological observations suggest the ... more Persisting tensions between high-redshift and low-redshift cosmological observations suggest the dark energy sector of the Universe might be more complex than the positive cosmological constant of the Lambda\LambdaLambdaCDM model. Motivated by string theory, wherein symmetry considerations make consistent AdS backgrounds (\textit (i.e.) maximally symmetric spacetimes with a negative cosmological constant) ubiquitous, we explore a scenario where the dark energy sector consists of two components: a negative cosmological constant, with a dark energy component with equation of state wphiw_{\phi}wphi on top. We test the consistency of the model against low-redshift Baryon Acoustic Oscillation and Type Ia Supernovae distance measurements, assessing two alternative choices of distance anchors: the sound horizon at baryon drag determined by the \textit{Planck} collaboration, and the Hubble constant determined by the SH0ES program. We find no evidence for a negative cosmological constant, and mild indicatio...

The Event Horizon Telescope has recently provided the first image of the dark shadow around the s... more The Event Horizon Telescope has recently provided the first image of the dark shadow around the supermassive black hole M87*. The observation of a highly circular shadow provides strong limits on deviations of M87*'s quadrupole moment from the Kerr value. We show that the absence of such a deviation can be used to constrain the physics of extra dimensions of spacetime. Focusing on the Randall-Sundrum AdS5 brane-world scenario, we show that the observation of M87*'s dark shadow sets the limit ℓ < ∼ 170 AU, where ℓ is the AdS5 curvature radius. This limit is among the first quantitative constraints on exotic physics obtained from the extraordinary first ever image of the dark shadow of a black hole.

Yu-Dai Tsai,1, 2, ∗ Youjia Wu,3, † Sunny Vagnozzi,4, ‡ and Luca Visinelli5, 6, § Fermi National A... more Yu-Dai Tsai,1, 2, ∗ Youjia Wu,3, † Sunny Vagnozzi,4, ‡ and Luca Visinelli5, 6, § Fermi National Accelerator Laboratory (Fermilab), Batavia, IL 60510, USA Kavli Institute for Cosmological Physics (KICP), University of Chicago, Chicago, IL 60637, USA Leinweber Center for Theoretical Physics, University of Michigan, Ann Arbor, MI 48109, USA Kavli Institute for Cosmology (KICC), University of Cambridge, Cambridge CB3 0HA, United Kingdom INFN, Laboratori Nazionali di Frascati, C.P. 13, I-100044 Frascati, Italy Tsung-Dao Lee Institute (TDLI), Shanghai Jiao Tong University, 200240 Shanghai, China (Dated: August 20, 2021)

arXiv: High Energy Physics - Phenomenology, 2020

We propose a new way of studying the Higgs potential at extremely high energies. The SM Higgs bos... more We propose a new way of studying the Higgs potential at extremely high energies. The SM Higgs boson, as a light spectator field during inflation in the early Universe, can acquire large field values from its quantum fluctuations which vary among different causal (Hubble) patches. Such a space dependence of the Higgs after the end of inflation leads to space-dependent SM particle masses and hence variable efficiency of reheating, when the inflaton decays to Higgsed SM particles. Inhomogeneous reheating results in (observable) temperature anisotropies. Further, the resulting temperature anisotropy spectrum acquires a significant non-Gaussian component, which is constrained by itPlanck{\it Planck}itPlanck observations of the Cosmic Microwave Background (CMB) and potentially detectable in next-generation experiments. Hence, in principle, observational searches for non-Gaussianity in the CMB can be used to constrain the dynamics of the Higgs boson at very high (inflationary) energies.

The duality relation between the electric and magnetic fields, in the presence of an additional a... more The duality relation between the electric and magnetic fields, in the presence of an additional axion-like field, is considered. We derive the new equations that describe the electrodynamics in this model, and we discuss the implications for the conservation of the electric and magnetic four-currents and for the propagation of waves.

arXiv: High Energy Physics - Phenomenology, 2008

The University of Utah, Physics Dept. 115 S 1400 E, Salt Lake City, UT USA 84112(Dated: October 2... more The University of Utah, Physics Dept. 115 S 1400 E, Salt Lake City, UT USA 84112(Dated: October 22, 2008)We present an expression for the transition probability between Dirac or Majorananeutrino flavors obtained from first principles within quantum field theory. Ourderivation is based on a standard quantum mechanical setup and includes the specificmechanism of neutrinoproduction only in as much as it specifies the initial state. Ourexpression for the transition probability reproduces the usual formula in the planewave limit and shows the correct non-relativistic and ultra-relativistic behaviors. Italso allows a simple understanding of the decoherence of the oscillations and of thequestion of the arrival times of the different neutrino mass eigenstates. We shownumerical examples for the case of two neutrino generations.

Physical Review D, 2022

We present an analytic study of the dispersion relation for an isotropic magnetized plasma intera... more We present an analytic study of the dispersion relation for an isotropic magnetized plasma interacting with axions. We provide a quantitative picture of the electromagnetic plasma oscillations in both the ultrarelativistic and nonrelativistic regimes and considering both non-degenerate and degenerate media, accounting for the dispersion curves as a function of the plasma temperature and the ratio of the plasma phase velocity to the characteristic velocity of particles. We include the modifications on the Landau damping of plasma waves induced by the presence of the axion field, and we comment on the effects of damping on subluminal plasma oscillations.

We derive a new integral equation that allows the calculation of the scattering or annihilation a... more We derive a new integral equation that allows the calculation of the scattering or annihilation amplitude of two particles subjected to two potentials when the corresponding amplitude for one potential only is known. We assume that scattering or annihilation occurs through one of the potentials, while the other potential affects the particle wave functions. Our expression is valid for any choice of the distorting potential and for any particle model. Our technique does not require the expansion of the amplitude into partial waves, and allows the study of models that are generally difficult to solve by means of the Schroedinger equation.

Sunny Vagnozzi, 2, ∗ Luca Visinelli, 4, 5, † Philippe Brax, ‡ Anne-Christine Davis, 1, § and Jere... more Sunny Vagnozzi, 2, ∗ Luca Visinelli, 4, 5, † Philippe Brax, ‡ Anne-Christine Davis, 1, § and Jeremy Sakstein ¶ Kavli Institute for Cosmology (KICC), University of Cambridge, Madingley Road, Cambridge CB3 0HA, United Kingdom∗∗ Institute of Astronomy (IoA), University of Cambridge, Madingley Road, Cambridge CB3 0HA, United Kingdom Istituto Nazionale di Fisica Nucleare (INFN), Laboratori Nazionali di Frascati, C.P. 13, I-100044 Frascati, Italy∗∗ Tsung-Dao Lee Institute (TDLI), Shanghai Jiao Tong University, 200240 Shanghai, China Gravitation Astroparticle Physics Amsterdam (GRAPPA), University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands Institute de Physique Theórique (IPhT), Université Paris-Saclay, CNRS, CEA, F-91191, Gif-sur-Yvette Cedex, France Department of Applied Mathematics and Theoretical Physics (DAMTP), Center for Mathematical Sciences, University of Cambridge, CB3 0WA, United Kingdom Department of Physics & Astronomy, University of Hawai‘i, Watanabe H...

The search for extra dimensions is a challenging endeavor to probe physics beyond the Standard Mo... more The search for extra dimensions is a challenging endeavor to probe physics beyond the Standard Model. The joint detection of gravity waves (GW) and electromagnetic (EM) signals from the merging of a binary system of compact objects like a neutron star (NS) can help constrain the geometry of extra dimensions. In particular, if our observable Universe is a 3+1 hypersurface or brane embedded in a higher 4+1 Anti-de Sitter (AdS$_5$) spacetime, in which gravity is the only field that propagates through the infinite bulk space while any other field is confined on the brane, then GW and EM signals between two points on the brane would in general travel different paths. This would result in a time lag between the detection of GW and EM signals emitted simultaneously from the same source, with the apparent measurement of a "superluminous" GW speed. Assuming the standard Lambda\LambdaLambda-Cold Dark Matter ($\Lambda$CDM) scenario, we set a bound on the AdS$_5$ radius of curvature $\ell \less...

Cosmic Microwave Background (CMB) observations are used to constrain reheating to Standard Model ... more Cosmic Microwave Background (CMB) observations are used to constrain reheating to Standard Model (SM) particles after a period of inflation. As a light spectator field, the SM Higgs boson acquires large field values from its quantum fluctuations during inflation, gives masses to SM particles that vary from one Hubble patch to another, and thereby produces large density fluctuations. We consider both perturbative and resonant decay of the inflaton to SM particles. For the case of perturbative decay from coherent oscillations of the inflaton after high scale inflation, we find strong constraints on the reheat temperature for the inflaton decay into heavy SM particles. For the case of resonant particle production (preheating) to (Higgsed) SM gauge bosons, we find temperature fluctuations larger than observed in the CMB for a range of gauge coupling that includes those found in the SM and conclude that such preheating cannot be the main source of reheating the Universe after inflation.

Classical and Quantum Gravity

Recently, Tsupko et al. have put forward the very interesting proposal to use the shadows of high... more Recently, Tsupko et al. have put forward the very interesting proposal to use the shadows of highredshift supermassive black holes (SMBHs) as standard rulers. This would in principle allow us to probe the expansion history within a redshift range which would otherwise be challenging to access. In this note, we critically examine this proposal, and identify a number of important issues which had been previously overlooked. These include difficulties in obtaining reliable SMBH mass estimates and reaching the required angular resolution, and an insufficient knowledge of the accretion dynamics of high-redshift SMBHs. While these issues currently appear to prevent high-redshift SMBH shadows from being used as robust standard rulers, we hope that our flagging them early will help in making this probe theoretically mature by the time it will be experimentally feasible.

Monthly Notices of the Royal Astronomical Society, 2021

We consider the observational constraints on stupendously large black holes (SLABs) in the mass r... more We consider the observational constraints on stupendously large black holes (SLABs) in the mass range Mgtrsim1011,mathrmModotM \gtrsim 10^{11}\, \mathrm{ M_{\odot}}Mgtrsim1011,mathrmModot. These have attracted little attention hitherto, and we are aware of no published constraints on a SLAB population in the range (1012–$10^{18})\, \mathrm{ M_{\odot}}$. However, there is already evidence for black holes of up to nearly 1011,mathrmModot10^{11}\, \mathrm{ M_{\odot}}1011,mathrmModot in galactic nuclei, so it is conceivable that SLABs exist and they may even have been seeded by primordial black holes. We focus on limits associated with (i) dynamical and lensing effects, (ii) the generation of background radiation through the accretion of gas during the pre-galactic epoch, and (iii) the gamma-ray emission from the annihilation of the halo of weakly interacting massive particles expected to form around each SLAB if these provide the dark matter. Finally, we comment on the constraints on the mass of ultralight bosons from future measurements of the mass and spin...

Scopo di questo esperimento è quello di stimare la velocità del suono nell’aria attraverso l’anal... more Scopo di questo esperimento è quello di stimare la velocità del suono nell’aria attraverso l’analisi dei picchi di risonanza all’interno di un tubo chiuso alle due estremità. Ci proponiamo inoltre di verificare l’esattezza del modello teorico utilizzato per determinare l’andamento dell’ampiezza dell’onda a regime in funzione della frequenza. L’apparato strumentale a disposizione consiste in un cilindro chiuso ai due estremi, di lunghezza L = (88.5 ± 0.2)cm e di diametro (8.05 ± 0.2)cm, sommariamente isolato poiché posto entro polistirolo. Ad una estremità è presente un altoparlante collegato a un generatore di onde (sorgente) a frequenza variabile controllata dal computer attraverso una scheda di I/O; all’altro estremo è presente un microfono (ricevitore) che trasmette il segnale elettrico convertito alla scheda di acquisizione.

We review the landscape of QCD axion models. Theoretical constructions that extend the window for... more We review the landscape of QCD axion models. Theoretical constructions that extend the window for the axion mass and couplings beyond conventional regions are highlighted and classified. Bounds from cosmol- ogy, astrophysics and experimental searches are reexamined and updated.