V. A. Rubakov

Russian Academy of Sciences, Moskva, Moscow, Russia

Are you V. A. Rubakov?

Claim your profile

Publications (188)492.51 Total impact

  • Source
    M. Libanov, V. Rubakov, S. Sibiryakov
    [Show abstract] [Hide abstract]
    ABSTRACT: We propose a holographic dual for (pseudo-)conformal cosmological scenario, with a scalar field that forms a moving domain wall in adS_5. The domain wall separates two vacua with unequal energy densities. Unlike in the existing construction, the 5d solution is regular in the relevant space-time domain.
  • Source
    S. A. Mironov, S. R. Ramazanov, V. A. Rubakov
    [Show abstract] [Hide abstract]
    ABSTRACT: We consider a non-inflationary early Universe scenario in which relevant scalar perturbations get frozen out at some point, but then are defrosted and follow a long nearly Minkowskian evolution before the hot era. This intermediate stage leaves specific imprint on the CMB 3-point function, largely independent of details of microscopic physics. In particular, the CMB bispectrum undergoes oscillations in the multipole l space with roughly constant amplitude. The latter is in contrast to the oscillatory bispectrum enhanced in the flattened triangle limit, as predicted by inflation with non-Bunch--Davies vacuum. Given this and other peculiar features of the bispectrum, stringent constraints imposed by the Planck data may not apply. The CMB 3-point function is suppressed by the inverse duration squared of the Minkowskian evolution, but can be of observable size for relatively short intermediate Minkowskian stage.
    Journal of Cosmology and Astroparticle Physics 12/2013; 2014(04). · 6.04 Impact Factor
  • V. A. Rubakov
    [Show abstract] [Hide abstract]
    ABSTRACT: The null energy condition (NEC) can be violated in a consistent way in models with unconventional kinetic terms, notably, in Galileon theories and their generalizations. We make use of one of these, the scale-invariant kinetic braiding model, to discuss whether a universe can in principle be created by manmade processes. We find that, even though the simplest models of this sort can have both healthy Minkowski vacuum and a consistent NEC-violating phase, there is an obstruction for creating a universe in a straightforward fashion. To get around this obstruction, we design a more complicated model and present a scenario for the creation of a universe in the laboratory.
    Physical Review D 08/2013; 88(4). · 4.69 Impact Factor
  • Source
    M. Osipov, V. Rubakov
    [Show abstract] [Hide abstract]
    ABSTRACT: We consider a simple cosmological model that includes a long ekpyrotic contraction stage and smooth bounce after it. Ekpyrotic behavior is due to a scalar field with a negative exponential potential, whereas the Galileon field produces bounce. We give an analytical picture of how the bounce occurs within the weak gravity regime, and then perform numerical analysis to extend our results to a non-perturbative regime.
    Journal of Cosmology and Astroparticle Physics 03/2013; · 6.04 Impact Factor
  • Source
    V. A. Rubakov, M. Yu. Kuznetsov
    [Show abstract] [Hide abstract]
    ABSTRACT: We address the question of whether or not fermions with twisted periodicity condition suppress the semiclassical decay of M^4xS^1 Kaluza--Klein vacuum. We consider a toy (1+1)-dimensional model with twisted fermions in cigar-shaped Euclidean background geometry and calculate the fermion determinant. We find that contrary to expectations, the determinant is finite. We consider this as an indication that twisted fermions do not stabilize the Kaluza--Klein vacuum.
    Theoretical and Mathematical Physics 05/2012; 175(1). · 0.67 Impact Factor
  • M. V. Libanov, V. A. Rubakov
    [Show abstract] [Hide abstract]
    ABSTRACT: We consider a scenario in which primordial scalar perturbations are generated when a complex conformal scalar field rolls down its negative quartic potential. Initially, these are perturbations of the phase of this field, which are then converted into adiabatic perturbations of the density. The existence of perturbations in the radial field direction, which have a red power spectrum, is a potentially dangerous feature of this scenario. But we show that in the linear order in the small parameter, the self-coupling, the infrared effects are completely nullified by an appropriate field redefinition. We evaluate the statistical anisotropy inherent in the model because of the presence of the long-wave perturbations of the radial field component. In the linear order in the self-coupling, the infrared effects do not affect the statistical anisotropy. They are manifested only at the quadratic order in the self-coupling, weakly (logarithmically) enhancing the corresponding contribution to the statistical anisotropy. The resulting statistical anisotropy is a combination of a large term, which decreases as the momentum increases, and a momentum-independent nonamplified term.
    Theoretical and Mathematical Physics 02/2012; 170(2). · 0.67 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We obtain a new bound on the value of Peskin-Takeuchi S parameter in a wide class of bottom-up holographic models for technicolor. Namely, we show that weakly coupled holographic description in these models implies S>>0.2. Our bound is in conflict with the results of electroweak precision measurements, so it strongly disfavors the models we consider.
    Physics Letters B 01/2012; 716(2). · 4.57 Impact Factor
  • V. A.rubakov
    [Show abstract] [Hide abstract]
    ABSTRACT: In this concluding talk at the last pre-LHC ICHEP event, a personal view of what is happening in theory, experiment and to some extent cosmology is given.
    International Journal of Modern Physics A 01/2012; 22(30). · 1.13 Impact Factor
  • Source
    S. L.dubovsky, V. A.rubakov
    [Show abstract] [Hide abstract]
    ABSTRACT: We argue that any viable mechanism of gauge field localization should automatically imply charge universality on the brane. We study whether this condition is satisfied in the two known proposals aimed to localize vector field in flat bulk space. We construct a simple calculable model with confinement in the bulk and deconfinement on the brane, as in the Shifman–Dvali set-up. We find that in our model the four-dimensional Coulomb law is indeed reproduced on the brane due to the massless localized photon mode. The charge universality is enforced by the presence of "confining strings." On the other hand, charge universality condition is not satisfied in another, brane-induced localization mechanism when the number of extra dimensions d is larger than two. We demonstrate that in the non-Abelian case the gauge fields inside the brane are never four-dimensional and their self-interaction is strong at all distances of interest. Hence this mechanism does not work for d > 2. At d = 2 the charge universality is still a problem, but it holds automatically at d = 1. At d = 1, however, the bulk gauge fields are strongly coupled in the non-Abelian case.
    International Journal of Modern Physics A 01/2012; 16(26). · 1.13 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The one loop effective potential of cold dense fermionic matter is calculated in the standard electroweak theory. It is shown that the anisotropic W-boson condensate is formed at sufficiently high density and B≠L. The anisotropic part of the energy-momentum tensor is calculated for this state. It is shown that this state is metastable, the instability being due to the electroweak baryon number violating transitions.
    International Journal of Modern Physics A 01/2012; 03(05). · 1.13 Impact Factor
  • Kh. S.nirov, V.a.rubakov
    [Show abstract] [Hide abstract]
    ABSTRACT: Emission of hard microscopic string (graviton) by an excited macroscopic string may be viewed as a model of branching of a (1+1)-dimensional baby universe off large parent one. We show that, apart from a trivial factor, the total emission rate is not suppressed by the size of the macroscopic string. This implies unsuppressed loss of quantum coherence in (1+1)-dimensional parent universe.
    Modern Physics Letters A 11/2011; 10(39). · 1.11 Impact Factor
  • V. A.rubakov, D. V.semikoz
    [Show abstract] [Hide abstract]
    ABSTRACT: Zero fermion modes are found explicitly for complex background gauge field configurations on contours in complex time plane relevant to multiparticle high energy scattering processes in (1 + 1)-dimensional Abelian Higgs model. Their number is determined by the topological number in accord with the triangle anomaly. The analog of the fermion level crossing is described. So, the analysis of the non-conservation of fermion quantum numbers is naturally generalized to complex background fields.
    Modern Physics Letters A 11/2011; 08(15). · 1.11 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: It is not totally excluded that there exists the fourth generation of quarks with masses in the TeV region. In that case they may form non-topological solitons. We discuss experimental signatures of their decays which differ them from conventional perturbative decays of very heavy fermions. These signatures are the number of the Higgs bosons produced and their spectrum.
    Modern Physics Letters A 11/2011; 07(17). · 1.11 Impact Factor
  • V. A.rubakov, M. E.shaposhnikov
    [Show abstract] [Hide abstract]
    ABSTRACT: On the basis of recent discussion of the effects due to topological changes, it is conjectured that the actual values of coupling constants of nature are most probably near the boundary of the anthropogenesis region in the space of all coupling constants.
    Modern Physics Letters A 11/2011; 04(02). · 1.11 Impact Factor
  • Source
    M. Libanov, V. Rubakov
    [Show abstract] [Hide abstract]
    ABSTRACT: We discuss two versions of the conformal scenario for generating scalar cosmological perturbations: a spectator version with a scalar field conformally coupled to gravity and carrying negligible energy density, and a dynamical version with a scalar field minimally coupled to gravity and dominating the cosmological evolution. By making use of the Newtonian gauge, we show that (i) no UV strong coupling scale is generated below $M_{Pl}$ due to mixing with metric perturbations in the dynamical scenario, and (ii) the dynamical and spectator models yield identical results to the leading non-linear order. We argue that these results, which include potentially observable effects like statistical anisotropy and non-Gaussianity, are characteristic of the entire class of conformal models. As an example, we reproduce, within the dynamical scenario and working in comoving gauge, our earlier result on the statistical anisotropy, which was originally obtained within the spectator approach.
  • Source
    M. Libanov, S. Mironov, V. Rubakov
    [Show abstract] [Hide abstract]
    ABSTRACT: We consider theories which explain the flatness of the power spectrum of scalar perturbations in the Universe by conformal invariance, such as conformal rolling model and Galilean Genesis. We show that to the leading {\it non-linear} order, perturbations in all models from this class behave in one and the same way, at least if the energy density of the relevant fields is small compared to the total energy density (spectator approximation). We then turn to the intrinsic non-Gaussianities in these models (as opposed to non-Gaussianities that may be generated during subsequent evolution). The intrinsic bispectrum vanishes, so we perform the complete calculation of the trispectrum and compare it with the trispecta of local forms in various limits. The most peculiar feature of our trispectrum is a (fairly mild) singularity in the limit where two momenta are equal in absolute value and opposite in direction (folded limit). Generically, the intrinsic non-Gaussianity can be of detectable size.
    Physical review D: Particles and fields 05/2011; 84.
  • Source
    M. Libanov, S. Ramazanov, V. Rubakov
    [Show abstract] [Hide abstract]
    ABSTRACT: Scalar cosmological perturbations with nearly flat power spectrum may originate from perturbations of the phase of a scalar field conformally coupled to gravity and rolling down negative quartic potential. We consider a version of this scenario whose specific property is a long intermediate stage between the end of conformal rolling and horizon exit of the phase perturbations. Such a stage is natural, e.g., in cosmologies with ekpyrosis or genesis. Its existence results in small negative scalar tilt, statistical anisotropy of all even multipoles starting from quardupole of general structure (in contrast to the usually discussed single quadrupole of special type) and non-Gaussianity of a peculiar form.
    Journal of Cosmology and Astroparticle Physics 02/2011; 6(06). · 6.04 Impact Factor
  • Dmitry S. Gorbunov, V. A. Rubakov
    [Show abstract] [Hide abstract]
    ABSTRACT: 1. Jeans instability in Newtonian gravity. 1.1. Jeans instability in static background. 1.2. Development of instability in expanding universe. 1.3. Linear sizes of perturbations and masses of objects -- 2. Cosmological perturbations in general relativity. Equations of linearized theory. 2.1. Background metric. 2.2. Generalities. 2.3. Equations in helicity sectors. 2.4. Regimes of evolution. 2.5. Scalar field condensate as dark matter -- 3. Evolution of vector and tensor perturbations. 3.1. Vector modes. 3.2. Tensor modes: Relic gravity waves -- 4. Scalar perturbations: Single-component fluids. 4.1. Master equation. 4.2. Relativistic matter. 4.3. Non-relativistic matter. 4.4. Matter perturbations at [symbol] domination -- 5. Primordial perturbations in real universe. 5.1. Adiabatic and isocurvature modes. 5.2. Adiabatic mode in superhorizon regime. 5.3. Initial data for isocurvature modes. 5.4. Primordial spectra: Results from observations. 5.5. Evolution of adiabatic perturbations: A preview -- 6. Scalar perturbations before recombination. 6.1. Adiabatic modes of large wavelengths. 6.2. Adiabatic modes entering the sound horizon at radiation domination. 6.3. Adiabatic perturbations of intermediate momenta. 6.4. CDM isocurvature perturbations. 6.5. Baryon isocurvature perturbations -- 7. Structure formation. 7.1. Matter perturbations after recombination: Linear regime. 7.2. Beginning of non-linear regime.8. Beyond ideal fluid approximation. 8.1. Distribution functions and Boltzmann equation in curved space-time. 8.2. General equations for scalar perturbations. 8.3. Warm dark matter. 8.4. Neutrino free streaming. 8.5. Photons and baryons at recombination epoch -- 9. Temperature of cosmic microwave background. 9.1. CMB temperature anisotropy. 9.2. Temperature anisotropy in instant photon decoupling approximation. 9.3. Small angular scales. 9.4. Anisotropy spectrum and cosmological parameters. 9.5. Temperature anisotropy generated by isocurvature modes -- 10. CMB polarization. 10.1. Sources of CMB polarization. 10.2. Polarization tensor. E- and B-modes. 10.3. Generation of CMB polarization. 10.4. Discussion -- 11. Drawbacks of the hot big bang theory. Inflation as possible way out. 11.1. Drawbacks of the hot big bang theory. 11.2. Inflation: The basic idea -- 12. Inflation in slow roll regime. 12.1. Slow roll conditions. 12.2. Inflationary models -- 13. Generation of cosmological perturbations at inflation. 13.1. Simplified analysis: Inflaton fluctuations. 13.2. Scalar perturbations in full linear theory. 13.3. Tensor perturbations. 13.4. Amplitudes and tilts of power spectra. 13.5. Discussion -- 14. Further aspects of inflationary theory. 14.1. Eternal inflation. 14.2. Generation of scalar perturbations by curvaton mechanism. 14.3. Light scalar field in inflating universe. 14.4. Axion as dark matter candidate: CDM isocurvature Mode -- 15. Preheating after inflation. 15.1. Inflaton decay in weakly coupled models. 15.2. Inflaton decay in a model with quadratic potential. 15.3. Peculiarities of [symbol]. 15.4. Creation of heavy fermions. 15.5. Physics applications -- 16. Bouncing universe. 17. Color pages.
  • Source
    M. Libanov, S. Mironov, V. Rubakov
    [Show abstract] [Hide abstract]
    ABSTRACT: Primordial scalar perturbations may be generated when complex conformal scalar field rolls down its negative quartic potential. We begin with the discussion of peculiar infrared properties of this scenario. We then consider the statistical anisotropy inherent in the model. Finally, we discuss the non-Gaussianity of scalar perturbations. Because of symmetries, the bispectrum vanishes identically. We present a general expression for the trispectrum and give its explicit form in the folded limit.
    Progress of Theoretical Physics Supplement 12/2010; 190. · 1.25 Impact Factor
  • Source
    Valery Rubakov, Andrey Vlasov
    [Show abstract] [Hide abstract]
    ABSTRACT: We give an account, at non-expert and quantitative level, of physics behind the CMB temperature anisotropy and polarization and their peculiar features. We discuss, in particular, how cosmological parameters are determined from the CMB measurements and their combinations with other observations. We emphasize that CMB is the major source of information on the primordial density perturbations and, possibly, gravitational waves, and discuss the implication for our understanding of the extremely early Universe.
    Physics of Atomic Nuclei 08/2010; · 0.54 Impact Factor

Publication Stats

7k Citations
492.51 Total Impact Points


  • 1978–2014
    • Russian Academy of Sciences
      • • Institute for Nuclear Research
      • • Institute of Nuclear Research
      Moskva, Moscow, Russia
  • 2013
    • Université Libre de Bruxelles
      Bruxelles, Brussels Capital Region, Belgium
  • 1978–2013
    • Lomonosov Moscow State University
      Moskva, Moscow, Russia
  • 2011
    • Moscow State Textile University
      Moskva, Moscow, Russia
  • 2004
    • Moscow Institute of Physics and Technology
      Moskva, Moscow, Russia
  • 2000
    • Durham University
      • Centre for Particle Theory
      Durham, ENG, United Kingdom
  • 1999
    • University of Cambridge
      Cambridge, England, United Kingdom
  • 1983–1998
    • Abdus Salam International Centre for Theoretical Physics
      Trst, Friuli Venezia Giulia, Italy
  • 1986–1993
    • CERN
      Genève, Geneva, Switzerland
    • Kyoto University
      Kioto, Kyōto, Japan
  • 1988
    • Deutsches Elektronen-Synchrotron
      Hamburg, Hamburg, Germany