Thursday, November 11, 2021

One often unrecognised reason for the appeal of BJP

What went wrong?







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Sunday, September 29, 2019

Recent advancements in fundamental physics


Recent experimental discoveries...


  • 2016: Discovery of gravitational waves,
  • 2013: Discovery of SM Higgs boson,
  • 1990-2015: Establishing the SM of cosmology,
  • 1998: Discovery of late time acceleration of the Universe,
  • Evidence in favour of existence of Cold Dark Matter,
  • 1995: Top quark,
  • Neutrino masses.

Recent (last 40 years) major theoretical advancements...

  • Mid 2010s: Amplitudes;
  • Early 2000s: Moduli stabilisation in string theory,
  • 1997: Dualities in general and AdS/CFT correspondence in particular,
  • Mid 1990s: Microscopic calculation of entropy of BHs,
  • Early 1980s: Cosmic inflation.
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Monday, September 9, 2019

Some recent papers about inflationary cosmology

The Scale Factor Potential Approach to Inflation

David Benisty, Eduardo I. Guendelman, Emmanuel N. Saridakis
(Submitted on 4 Sep 2019)
We propose a new approach to investigate inflation in a model-independent way, and in particular to elaborate the involved observables, through the introduction of the "scale factor potential". Through its use one can immediately determine the inflation end, which corresponds to its first (and global) minimum. Additionally, we express the inflationary observables in terms of its logarithm, using as independent variable the e-folding number. After showing how the above procedure works in the case of Starobinsky inflation, we apply it in order to reconstruct physical scalar-field potentials that can generate any desirable inflationary observables. As an example, we construct a new class of scalar potentials that can lead to the desired spectral index and tensor-to-scalar ratio, in agreement with observations.
https://arxiv.org/abs/1909.01982

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Monday, June 24, 2019

Data science: resources

Resources:


Other resources:

Original gan paper 


some news & applications
Generative Adversarial Networks recover features in astrophysical images of galaxies beyond the 
deconvolution limit
https://machinelearningmastery.com/impressive-applications-of-generative-adversarial-networks/
http://karpathy.github.io/neuralnets/

Other Links:


Articles:
JP's work:

Books (math):

In physics and related fields:


  • PyTransport: A Python package for the calculation of inflationary correlation functions,
  • http://roban.github.io/CosmoloPy/
  • Python CAMB
  • https://ascl.net/;
  • http://www.usm.uni-muenchen.de/people/paech/Astro_Num_Lab/
  • http://python4astronomers.github.io/
  • https://www.coursera.org/learn/data-driven-astronomy
  • https://sydney.edu.au/news-opinion/news/2017/02/22/data-driven-astronomy.html
  • https://phys.org/news/2018-09-machine-astronomy.html
  • https://physicstoday.scitation.org/doi/pdf/10.1063/PT.3.3261
  • https://www.analyticsindiamag.com/why-machine-learning-is-a-great-career-jump-for-physicists/
  • https://physicsworld.com/a/a-machine-learning-revolution/
  • https://machine-learning-for-physicists.org/
  • https://physics.bu.edu/~pankajm/MLnotebooks.html
  • https://www.uwa.edu.au/research/machine-learning-applications-for-physical-sciences
  • http://www.ipam.ucla.edu/programs/workshops/machine-learning-for-physics-and-the-physics-of-learning-tutorials/
  • http://physics.bu.edu/~pankajm/PY895-ML.html
  • https://towardsdatascience.com/my-journey-from-physics-into-data-science-5d578d0f9aa6
  • http://darkmachines.org/
  • https://www.symmetrymagazine.org/article/studying-the-stars-with-machine-learning
  • https://arxiv.org/abs/1803.08823
  • https://arxiv.org/abs/1808.04728
  • https://arxiv.org/abs/1902.00522
  • https://arxiv.org/abs/1903.10563
  • https://arxiv.org/abs/1904.07248
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    Saturday, June 8, 2019

    Theoretical physics related resources



    Net Advance of physics: http://web.mit.edu/redingtn/www/netadv/


    HEP:
    1. Daniel Harlow (September 2019): link,
    2. Particle fever: link,
    3. The Fabric of the Cosmos: Universe or Multiverse? link,

    Popular level expositions: cosmology
    1. The first three minutes by Steven Weinberg,
    2. We have no idea: a guide to the unknown universe by Jorge Cham and Daniel Whiteson,
    3. The big bang by Simon Singh, 
    4. The inflationary universe by Alan Guth.

    Popular level expositions: string theory
    1. Is string phenomenology an oxymoron? https://arxiv.org/abs/1612.01569
    2. Life at the interface of particle physics and string theory: https://www.nikhef.nl/~t58/RMP_Extended_BW.pdf
    3. Witten: 2010 Newton medal: String theory and the Universe
    4. Shiraz Minwalla:
      1. 2018 talk on Quantum gravity and AdS/CFT,
      2. 2015 talk,


    More technical expositions:
    1. Matt Reece: ICTP summer school 2019: formal developments in HEP (WGC and swampland programme): lecture 01, 
    2. Shiraz Minwalla's older lectures on string theory,
      1. Introduction; action for a massive relativistic point particle; constraints and quantization;
    3. Shiraz Minwalla's 2018 lectures on string theory,
    4. Ashoke Sen's lectures on string compactifications,
    5. Ashoke Sen's lectures on Advanced QFT,
    6. Ashoke Sen's lectures on General Relativity,
    7. Ashoke Sen's lectures on Cosmology,
      1. Review of FRW universe, Review of thermodynamics: Micro-canonical ensemble.
      2. Review of statistical mechanics: grand-canonical ensemble, counting number of independent equations and variables in FRW cosmology.
      3. Properties of Statistical system with multiple components in thermal equilibrium , entropy conservation, relation of chemical potentials of particles and anti-particles, behaviour of number densities, energy densities and pressure for non-relativistic and relativistic particles.
      4. Quantitative statement of particle decoupling, decoupling of neutrinos in radiation dominated era, effective temperature after decoupling, wave number scaling after decoupling of a massive particle.
      5. State of the universe around 1 MeV temperature, ratios of photon and neutrino temperature, time of photon and neutrino decoupling.
      6. Continuation of studying evolution of the universe from 1MeV to 0.1 MeV energy scale, What happens to the hydrogen-helium ratio if there are additional massless particles or neutrino anti-neutrino number difference? numerical estimation of time scale and ratio of photon-neutrino temperature at various energy scale.
      7. Evolution of neutron-proton system in chemical equilibrium via weak interactions, derivation of neutron-proton ratio at temperature 1 MeV scale, evolution of neutron-proton using non-equilibrium dynamics below 1 MeV temperature.
      8. TBA
      9. Rate of change of neutron fraction with time in non-equilibrium dynamics, approximate analysis of nuclei formation , determination of hydrogen helium ratio in our universe.
      10. Re-derivation of helium to hydrogen ratio, Neucleosynthesis at 10^9 K temperature.
      11. Evaluation of deuteron number density, determination of temperature when photon goes out of equilibrium.
      12. Recombination
      13. TBA
      14. TBA
      15. Sakharov conditions
      16. Baryogenesis
      17. TBA
      18. Dark matter, WIMP
      19. Axionic dark matter, Horizon problem and it’s possible solution via inflation.
      20. Slow roll conditions, Constraints on inflaton potential, reheating.
      21. Scalar field driven inflation, Reheating temperature, Puzzle regarding non-homogeneity of CMB spectrum.
      22. Comoving Hubble radius, quantum fluctuations during inflation, two point function of inflaton field fluctuations
      23. Quantisation of inflaton fluctuation field, Bunch-Davies vacuum.
      24. Metric fluctuations during inflation.
      25. Study of metric perturbation, metric scalar mode fluctuation, two point correlation function of gauge invariant scalar mode fluctuations, scalar power spectrum, tensor power spectrum and their relationship with CMB spectrum, constraints on inflation energy scale.
      26. From CMB observation derivation of inflation scale and Lyth bound, spectral indices, physical interpretation of gauge invariant scalar perturbation.
      27. Identification of gauge invariant scalar fluctuations and strategy of their classical evolution in the super horizon range.
      28. Classical evolution of scalar perturbation, Initial condition during inflation.
      29. Computation of energy momentum tensor components for Inflation fluctuations during slow roll inflation, Classical evolution eq. in super-horizon era and eq. of state.
      30. Vector perturbation, Tensor perturbation, correlations in angular directions of last scattering surface, Observed CMB angular spectrum and the origin of oscillation in that spectrum.
      31. Angular correlation of scalar perturbation, Polarisation of CMB photons, Intensity tensor.
      32. Computation of CMB temperature fluctuations from the scalar fluctuations in times of inflation if the horizon re-entry happens in matter or radiation dominated era.
      33. Towards CMB observations.
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    Saturday, May 18, 2019

    Some recent papers...

    https://arxiv.org/abs/1906.02764

    Enhancement of the Axion Decay Constant in Inflation and the Weak Gravity Conjecture

    Pran Nath, Maksim Piskunov
    Models of axion inflation based on a single cosine potential require the axion decay constant f to be super-Planckian in size. However, f>MPlis disfavored by the Weak Gravity Conjecture (WGC). It is then pertinent to ask if one can construct axion inflation models in conformity with WGC. In this work we assume that WGC holds for the microscopic Lagrangian so that f<MPl. However, inflation is controlled by an effective Lagrangian much below the Planck scale where the inflaton is an effective axionic field associated with an effective decay constant fe which could be very different from f. In this work we propose a Coherent Enhancement Mechanism (CEM) for slow roll inflation controlled by flat potentials which can produce fe≫MPl while f<MPl. In the analysis we consider a landscape of chiral fields charged under a U(1) global shift symmetry and consider breaking of the U(1) symmetry by instanton type symmetry breaking terms. In the broken phase there is one light pseudo-Nambu-Goldstone-Boson (pNGB) which acts as the inflaton. We show that with an appropriate choice of symmetry breaking terms the inflaton potential is a superposition of many cosines and the condition that they produce a flat potential allows one to enhance fe so that fe/MPl≫1. We discuss the utility of this mechanism for a variety of inflaton models originating in supersymmetry and supergravity. The Coherent Enhancement Mechanism allows one to reduce an inflation model with an arbitrary potential to an effective model of natural inflation, i.e. with a single cosine, by expanding the potential near a field point where horizon exit occurs, and matching the expansion coefficients to those of natural inflation.




    https://arxiv.org/abs/1906.00986

    Direct anthropic bound on the weak scale from supernovae explosions

    Guido D'Amico, Alessandro Strumia, Alfredo Urbano, Wei Xue
    (Submitted on 3 Jun 2019)
    Core-collapse supernovae presumably explode because trapped neutrinos push the material out of the stellar envelope. This process is directly controlled by the weak scale v: we argue that supernova explosions happen only if fundamental constants are tuned within a factor of few as v∼Λ3/4QCDM1/4Pl, such that neutrinos are trapped in supernovae for a time comparable to the gravitational time-scale. We provide analytic arguments and simulations in spherical approximation, that need to be validated by more comprehensive simulations. The above result can be important for fundamental physics, because core-collapse supernova explosions seem anthropically needed, as they spread intermediate-mass nuclei presumably necessary for `life'. We also study stellar burning, finding that it does not provide anthropic boundaries on v.
    _________________________________________________________________________________

    https://arxiv.org/abs/1905.12421

    Hunting for extra dimensions in the shadow of M87*

    Sunny Vagnozzi, Luca Visinelli
    (Submitted on 29 May 2019)
    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 AdS5brane-world scenario, we show that the observation of M87*'s dark shadow sets the limit ℓ≲170AU, 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.
    _________________________________________________________________________________

    https://arxiv.org/abs/1905.10614

    Gravitational waves and extra dimensions: a short review

    Hao Yu, Zi-Chao Lin, Yu-Xiao Liu
    (Submitted on 25 May 2019)
    We give a brief review on the recent development of gravitational waves in extra-dimensional theories of gravity. Studying extra-dimensional theories with gravitational waves provides a new way to constrain extra dimensions. After a flash look at the history of gravitational waves and a brief introduction to several major extra-dimensional theories, we focus on the sources and spectra of gravitational waves in extra-dimensional theories. It is shown that one can impose limits on the size of extra dimensions and the curvature of the universe by researching the propagations of gravitational waves and the corresponding electromagnetic waves. Since gravitational waves can propagate throughout the bulk, how the amplitude of gravitational waves decreases determines the number of extra dimensions for some models. In addition, we also briefly present some other characteristics of gravitational waves in extra-dimensional theories.
    _________________________________________________________________________________
    https://arxiv.org/abs/1903.11820

    Small field models of inflation that predict a tensor-to-scalar ratio r=0.03

    Ira Wolfson, Ram Brustein
    (Submitted on 28 Mar 2019)
    Future observations of the cosmic microwave background (CMB) polarization are expected to set an improved upper bound on the tensor-to-scalar ratio of r≲0.03. Recently, we showed that small field models of inflation can produce a significant primordial gravitational wave signal. We constructed viable small field models that predict a value of r as high as 0.01. Models that predict higher values of r are more tightly constrained and lead to larger field excursions. This leads to an increase in tuning of the potential parameters and requires higher levels of error control in the numerical analysis. Here, we present viable small field models which predict r=0.03. We further find the most likely candidate among these models which fit the most recent Planck data while predicting r=0.03. We thus demonstrate that this class of small field models is an alternative to the class of large field models. The BICEP3 experiment and the Euclid and SPHEREx missions are expected to provide experimental evidence to support or refute our predictions.
    _________________________________________________________________________________

    https://arxiv.org/abs/1902.05559

    Supersymmetric Inflation from the Fifth Dimension

    Kaustubh Deshpande, Raman Sundrum
    (Submitted on 14 Feb 2019)
    We develop a supersymmetric bi-axion model of high-scale inflation coupled to supergravity, in which the axionic structure originates from, and is protected by, gauge symmetry in an extra dimension. While local supersymmetry (SUSY) is necessarily Higgsed at high scales during inflation we show that it can naturally survive down to the ∼ TeV scale in the current era in order to resolve the electroweak hierarchy problem. We show how a suitable inflationary effective potential for the axions can be generated at tree-level by charged fields under the higher-dimensional gauge symmetry. The inflationary trajectory lies along the lightest direction in the bi-axion field space, with periodic effective potential and an effective super-Planckian field range emerging from fundamentally sub-Planckian dynamics. The heavier direction in the field space is shown to also play an important role, as the dominant source of super-Higgsing during inflation. This model presents an interesting interplay of tuning considerations relating the electroweak hierarchy, cosmological constant and inflationary superpotential, where maximal naturalness favors SUSY breaking near the electroweak scale after inflation. The scalar superpartner of the axionic inflaton, the "sinflaton", can naturally have ∼ Hubble mass during inflation and sufficiently strong coupling to the inflaton to mediate primordial non-Gaussianities of observable strength in future 21-cm surveys. Non-minimal charged fields under the higher-dimensional gauge symmetry can contribute to periodic modulations in the CMB, within the sensitivity of ongoing measurements.
    _________________________________________________________________________________
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    One often unrecognised reason for the appeal of BJP

    What went wrong? https://thewire.in/politics/indias-left-liberals-need-an-urgent-mid-stream-correction https://theprint.in/national-interest...

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    • Some recent papers about inflationary cosmology
      The Scale Factor Potential Approach to Inflation David Benisty ,  Eduardo I. Guendelman ,  Emmanuel N. Saridakis (Submitted on 4 Sep 2...