A5074583516- Cosmology and Gravitation Theories
- Black Holes and Theoretical Physics
- Galaxies: Formation, Evolution, Phenomena
- Solar and Space Plasma Dynamics
- Geophysics and Gravity Measurements
- Pulsars and Gravitational Waves Research
- Dark Matter and Cosmic Phenomena
- Particle physics theoretical and experimental studies
- Noncommutative and Quantum Gravity Theories
- Astrophysical Phenomena and Observations
- Astronomy and Astrophysical Research
- Relativity and Gravitational Theory
- Advanced Thermodynamics and Statistical Mechanics
- Stochastic processes and financial applications
- Advanced Mathematical Theories and Applications
- Astrophysics and Cosmic Phenomena
- Quantum Mechanics and Applications
- Mental Health Research Topics
- Stellar, planetary, and galactic studies
- Adaptive optics and wavefront sensing
- Mechanics and Biomechanics Studies
- Digital Holography and Microscopy
- Radio Astronomy Observations and Technology
- Quantum Electrodynamics and Casimir Effect
- Atomic and Subatomic Physics Research
Institute for Research in Fundamental Sciences
2018-2024
Istituto Nazionale di Fisica Nucleare, Sezione di Bologna
2016-2018
Uppsala University
2010-2016
Lancaster University
2014
University of Michigan
2009-2010
University of Waterloo
2005-2006
Perimeter Institute
2005
We summarize the utility of precise cosmic microwave background (CMB) polarization measurements as probes physics inflation. focus on prospects for using CMB to differentiate various inflationary mechanisms. In particular, a detection primordial B‐mode would demonstrate that inflation occurred at very high energy scale, and inflaton traversed super‐Planckian distance in field space. explain how such or constraint illuminate aspects Planck scale. Moreover, can constrain scale‐dependence...
Releasing the 12.5-year pulsar timing array data, North American Nanohertz Observatory for Gravitational Waves (NANOGrav) has recently reported evidence a stochastic common-spectrum which would herald detection of gravitational wave background (SGWB) first time. We investigate if signal could be generated from end $\sim 10$ MeV but still phenomenologically viable double-field inflation when field configuration settles to its true vacuum. During at such scales, bubbles vacuum that can...
The BICEP2 experiment has announced a signal for primordial gravity waves with tensor-to-scalar ratio $r=0.2^{+0.07}_{-0.05}$ [arXiv:1403.3985]. There are two ways to reconcile this result the latest Planck [arXiv:1303.5082]. One is by assuming that there considerable tilt of $r$, $\mathcal{T}_r$, positive sign, $\mathcal{T}_r=d\ln r/d\ln k\gtrsim 0.57^{+0.29}_{-0.27}$ corresponding blue tensor modes order $n_T\simeq0.53 ^{+0.29}_{-0.27}$, best-fit value scalar power spectrum $n_S$. other...
The difficulty of building metastable vacua in string theory has led some to conjecture that, the landscape, potentials satisfy $\left|\nabla V/V\right|\geq c\sim \mathcal{O}(1)$. This condition, which is supported by different explicit constructions, suggests that EFTs lead de-Sitter belong what dubbed as swampland. condition endangers paradigm single field inflation. In this paper, we show how scalar excited initial states cannot rescue inflation from swampland, they produce large local...
We explicitly construct a double-field inflationary model, which satisfies the latest Planck constraints at cosmic microwave background (CMB) scales and produces whole dark matter energy density as primordial black holes (PBHs), in mass range $10^{-17}~M_{\odot}\lesssim M_{{}_{\rm PBH}}\lesssim 10^{-13}~M_{\odot}$. The PBHs can be produced after end of slow-roll inflation from bubbles true vacuum that nucleate during course inflation. Obtaining this enforces scale to extremely low, $10^{-7}...
In cascade inflation and some other string models, collisions of mobile branes with or orbifold planes occur lead to interesting cosmological signatures. The fundamental M/string-theory description these is still lacking but it clear that the inflaton looses part its energy form brane matter, e.g. a component tensionless strings. absence description, we assume general barotropic fluid on brane, which absorbs inflaton's energy. modeled by scalar suitable exponential potential arrive at...
The inflationary cosmology paradigm is very successful in explaining the CMB anisotropy to percent level. Besides dependence on model, power spectra, spectral tilt and non-Gaussianity of temperature fluctuations also depend initial state inflation. Here, we examine what extent these observables are affected by our ignorance condition for perturbations, due unknown new physics at a high scale M. For states that satisfy constraints from backreaction, find amplitude spectra could still be...
We identify a two-parameter family of excited states within slow-roll inflation for which either the corrections to two-point function or characteristic signatures in three-point -- i.e. enhancement flattened momenta configurations-- are absent. These may nonetheless violate adiabaticity condition maximally. dub these initial calm states. show that two sets do not intersect, i.e., those leave power-spectrum invariant can be distinguished from their bispectra, and vice versa. The same set...
We propose an inflationary scenario, M-flation, in which inflation is driven by three N × hermitian matrices Φi, i = 1, 2, 3. The potential of our model, strongly motivated from string theory, constructed Φi and their commutators. show that one can consistently restrict the classical dynamics to a sector are proportional irreducible representations SU(2). In this model effectively behaves as N-flation with 3N2 number fields effective inflaton field has super-Planckian value. Furthermore,...
We discuss the implications of a purely classical (instead quantum) theory gravity for primordial gravitational wave spectrum generated during inflation. argue that scalar field driven inflation in amplitude will be too small, irrespective its seed, to detected any forthcoming experiments. Therefore, positive detection B-mode polarizations Cosmic Microwave Background (CMB) naturally confirm quantum nature itself. Furthermore there no upper limit on scale case gravity, and high-scale model...
Abstract The standard cosmological model is in the midst of a stress test, thanks to tension between supernova-based measurements Hubble constant H 0 and inferences its values from cosmic microwave background (CMB) anisotropies. Numerous explanations for present-day acceleration require presence new fundamental scalar field, as do early dark energy solutions tension. This raises possibility that multiple fields cooperatively contribute component bursts throughout time due distinct initial...
This paper explicitly develops the three-field cosmological perturbation theory with a flat field space. We solve background and equations numerically for three different cases. First, to check consistency of formalism, we investigate an effective two-field model motivated by two-block case multi-giant vacua matrix Inflation model. Then completely without any direct interaction between fields, finally, containing interactions. The power spectra curvature perturbations in all cases are...
According to most inflationary models, fluctuations that are of cosmological size today started out much smaller than any plausible cutoff length such as the string or Planck lengths. It has been shown this could open an experimental window for testing models short-scale structure space-time. The observability effects hinges crucially, however, on initial conditions imposed new comoving modes which continually being created at scale. Here, we address question while modeling space-time...
Inflation has the potential to seed galactic magnetic fields observed today. However, there is an obstacle amplification of quantum fluctuations electromagnetic field during inflation: namely, conformal invariance theory on a conformally flat underlying geometry. As existence preferred minimal length breaks background geometry, it plausible that this effect could induce amplification. We show scenario equivalent endowing photon with large negative mass inflation. This effective negligibly...
The power spectrum of M-theory cascade inflation is derived. It possesses three distinctive signatures: a decisive suppression at small scales, oscillations around the scales that cross horizon when inflaton potential jumps and stepwise decrease in scalar spectral index. All properties result from features potential. Cascade realizes assisted heterotic driven by non-perturbative interactions N M5-branes. are generated whenever two M5-branes collide with boundaries. derived small-scale serves...
In this paper we study gauged M-flation, an inflationary model in which inflation is driven by three N × scalar field matrices the adjoint representation of U(N) gauge group. We focus our on M-flation could be derived from dynamics a stack D3-branes appropriate background flux. The unaltered compared to ungauged case \cite{Ashoorioon:2009wa}, while spectrum ``spectator species'', isocurvature modes, differs case. Presence large number spectators, although irrelevant slow-roll dynamics, has...
We investigate the effect of non-linear dispersion relations on bispectrum. In particular, we study case were modified do not violate WKB condition at early times, focusing a particular example which is exactly solvable: Jacobson-Corley relation with quartic correction positive coefficient to squared linear relation. find that corrections standard result for bispectrum are suppressed by factor H2/pc2 where pc scale modification becomes relevant. The mildly configuration-dependent and...
Accelerating supermassive black holes, connected to cosmic strings, could contribute structure formation and get captured by galaxies if their velocities are small. This would mean that the acceleration of these holes is small too. Such a slow has no significant effect on shadow such holes. We also show that, for slowly accelerating angular position images in gravitational lensing effects do not change significantly. propose method observe through lensing. The based observation differential...
Most of the inflationary scenarios that try to explain origin Primordial Black Holes (PBHs) from enhancements power spectrum values order one, at relevant scales, run into clashes with Effective Field Theory (EFT) criteria or fail enhance such large amplitudes. In this paper, we unravel a mechanism for enhancing during inflation does not use flattening potential reduction sound speed scalar perturbations. The is based on observation in formalism Extended EFT (EEFToI) sixth polynomial...
The previous proposal (by two of us) chain inflation with the QCD axion is shown to fail. involved a series fast tunneling events, yet here it that too slow. We calculate bubble nucleation rates for phase transitions in thick wall limit, approximating barrier by triangle. A similar problem arises realization string landscape uses minima along monodromy staircase around conifold point. basic potential are far apart allow rapid enough these models. entertain possibility overcoming this...
Recently we introduced an inflationary setup in which the inflaton fields are matrix valued scalar with a generic quartic potential, M-flation. In this work study landscape of various models arising from The potential arises dynamics concentric multiple branes appropriate flux compactifications string theory. After discussing classical theory possibility transition among appearing at different points on landscape, mapping quantum As specific examples, some two-field landscape.