V. A. Rubakov

Lomonosov Moscow State University, Moskva, Moscow, Russia

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Publications (198)609.71 Total impact

  • Source
    M. Libanov · V. Rubakov · G. Rubtsov
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    ABSTRACT: Approximate de Sitter symmetry of inflating Universe is responsible for the approximate flatness of the power spectrum of scalar perturbations. However, this is not the only option. Another symmetry which can explain nearly scale-invariant power spectrum is conformal invariance. We give a short review of models based on conformal symmetry which lead to the scale-invariant spectrum of the scalar perturbations. We discuss also potentially observable features of these models.
    Full-text · Article · Aug 2015 · JETP Letters
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    ABSTRACT: This paper describes the physics case for a new fixed target facility at CERN SPS. The SHiP (Search for Hidden Particles) experiment is intended to hunt for new physics in the largely unexplored domain of very weakly interacting particles with masses below the Fermi scale, inaccessible to the LHC experiments, and to study tau neutrino physics. The same proton beam setup can be used later to look for decays of tau-leptons with lepton flavour number non-conservation, $\tau\to 3\mu$ and to search for weakly-interacting sub-GeV dark matter candidates. We discuss the evidence for physics beyond the Standard Model and describe interactions between new particles and four different portals - scalars, vectors, fermions or axion-like particles. We discuss motivations for different models, manifesting themselves via these interactions, and how they can be probed with the SHiP experiment and present several case studies. The prospects to search for relatively light SUSY and composite particles at SHiP are also discussed. We demonstrate that the SHiP experiment has a unique potential to discover new physics and can directly probe a number of solutions of beyond the Standard Model puzzles, such as neutrino masses, baryon asymmetry of the Universe, dark matter, and inflation
    Full-text · Article · Apr 2015
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    M. Libanov · V. Rubakov
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    ABSTRACT: We point out that the (pseudo-)conformal Universe scenario may be realized as decay of conformally invariant, metastable vacuum, which proceeds via spontaneous nucleation and subsequent growth of a bubble of a putative new phase. We study perturbations about the bubble and show that their leading late-time properties coincide with those inherent in the original models with homogeneously rolling backgrounds. In particular, the perturbations of a spectator dimension-zero field have flat power spectrum.
    Full-text · Article · Feb 2015 · Physical Review D

  • No preview · Article · Dec 2014 · Russian Mathematical Surveys
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    M. Libanov · V. Rubakov · S. Sibiryakov
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    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.
    Full-text · Article · Sep 2014 · Physics Letters B
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    V. A. Rubakov
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    ABSTRACT: We give a mini-review of scalar field theories with second-derivative Lagrangians, whose field equations are second order. Some of these theories admit solutions violating the Null Energy Condition and having no obvious pathologies. We give a few examples of using these theories in cosmological setting and also in the context of the creation of a universe in the laboratory.
    Preview · Article · Jan 2014 · Physics-Uspekhi
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    S. A. Mironov · S. R. Ramazanov · V. A. Rubakov
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    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.
    Preview · Article · Dec 2013 · Journal of Cosmology and Astroparticle Physics
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    Andrei Khmelnitsky · Valery Rubakov
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    ABSTRACT: An ultralight free scalar field with mass around 10^{-23} - 10^{-22} eV is a viable dark mater candidate, which can help to resolve some of the issues of the cold dark matter on sub-galactic scales. We consider the gravitational field of the galactic halo composed out of such dark matter. The scalar field has oscillating in time pressure, which induces oscillations of gravitational potential with amplitude of the order of 10^{-15} and frequency in the nanohertz range. This frequency is in the range of pulsar timing array observations. We estimate the magnitude of the pulse arrival time residuals induced by the oscillating gravitational potential. We find that for a range of dark matter masses, the scalar field dark matter signal is comparable to the stochastic gravitational wave signal and can be detected by the planned SKA pulsar timing array experiment.
    Preview · Article · Sep 2013 · Journal of Cosmology and Astroparticle Physics
  • V. A. Rubakov
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    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.
    No preview · Article · Aug 2013 · Physical Review D
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    V. A. Rubakov
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    ABSTRACT: 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 man-made processes. We find that even though the simplest models of this sort can have both healthy Minkowski vacuum and 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.
    Preview · Article · May 2013
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    M. Osipov · V. Rubakov
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    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.
    Preview · Article · Mar 2013 · Journal of Cosmology and Astroparticle Physics
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    E. Krylov · A. Levin · V. Rubakov
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    ABSTRACT: We consider a mechanism of dark matter production in the course of first order phase transition. We assume that there is an asymmetry between X- and anti-X-particles of dark sector. In particular, it may be related to the baryon asymmetry. We also assume that the phase transition is so strongly first order, that X-particles do not permeate into the new phase. In this case, as the bubbles of old phase collapse, X-particles are packed into Q-balls with huge mass defect. These Q-balls compose the present dark matter. We find that the required present dark matter density is obtained for the energy scale of the theory in the ballpark of 1-10 TeV. As an example we consider a theory with effective potential of one-loop motivated form.
    Preview · Article · Jan 2013 · Physical review D: Particles and fields
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    M. V. Libanov · V. A. Rubakov
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    ABSTRACT: We consider two versions of the scenario for generating scalar cosmological perturbations based on the conformal symmetry: a spectator version with a scalar field conformally coupled to gravity and with a negligible energy density; a dynamical version with a scalar field minimally coupled to gravity and dominating the cosmological evolution. Using the Newtonian gauge, we show, first, that no UV strong-coupling scale is generated below MPl , because of mixing with metric perturbations in the dynamical scenario, and, second, that both the dynamical and the spectator models yield identical results in the leading nonlinear order. These results, which include potentially observable effects like statistical anisotropy and non-Gaussianity, hold for the entire class of conformal models. As an example, in the dynamical scenario with the comoving gauge, we reproduce our result on the statistical anisotropy, previously obtained in the framework of the spectator approach.
    Full-text · Article · Oct 2012 · Theoretical and Mathematical Physics
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    V. A. Rubakov · M. Yu. Kuznetsov
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    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.
    Preview · Article · May 2012 · Theoretical and Mathematical Physics
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    M. V. Libanov · V. A. Rubakov
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    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.
    Full-text · Article · Feb 2012 · Theoretical and Mathematical Physics
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    D.G. Levkov · V. A. Rubakov · S.V. Troitsky · Y. A. Zenkevich
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    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.
    Full-text · Article · Jan 2012 · Physics Letters B
  • D.v.deryagin · D. Yu.grigoriev · V.a.rubakov
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    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.
    No preview · Article · Jan 2012 · International Journal of Modern Physics A
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    S. L.dubovsky · V. A.rubakov
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    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.
    Preview · Article · Jan 2012 · International Journal of Modern Physics A
  • V. A.rubakov
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    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.
    No preview · Article · Jan 2012 · International Journal of Modern Physics A
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    A.levin · V.rubakov
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    ABSTRACT: We consider Friedberg–Lee–Sirlin Q-balls in a (3+1)-dimensional model with vanishing scalar potential of one of the fields. We show that, unlike in (2+1) and (1+1) dimensions, the Q-ball is stabilized by the gradient energy of this field and carries scalar charge, over and beyond the global charge. The latter property is also inherent in a model with the scalar potential that does not vanish in a finite field region near the origin.
    Preview · Article · Nov 2011 · Modern Physics Letters A

Publication Stats

9k Citations
609.71 Total Impact Points

Institutions

  • 1978-2015
    • Lomonosov Moscow State University
      • • Department of Biophysics at the Faculty of Physics
      • • Department of Particle Physics and Cosmology
      • • Division of Physics
      Moskva, Moscow, Russia
  • 1978-2014
    • Russian Academy of Sciences
      • Institute for Nuclear Research
      Moskva, Moscow, Russia
  • 2013
    • Université Libre de Bruxelles
      Bruxelles, Brussels Capital Region, Belgium
  • 2011
    • Moscow State Forest University
      Mytishi, Moskovskaya, Russia
  • 2000
    • Max Planck Institute for Physics
      München, Bavaria, Germany
  • 1999
    • University of Cambridge
      Cambridge, England, United Kingdom
  • 1998
    • Boston University
      • Department of Physics
      Boston, Massachusetts, United States
  • 1983-1998
    • Abdus Salam International Centre for Theoretical Physics
      Trst, Friuli Venezia Giulia, Italy
  • 1993
    • University of Minnesota Duluth
      Duluth, Minnesota, United States
  • 1988
    • Deutsches Elektronen-Synchrotron
      Hamburg, Hamburg, Germany
  • 1987
    • IT University of Copenhagen
      København, Capital Region, Denmark
  • 1986
    • CERN
      Genève, Geneva, Switzerland
    • Kyoto University
      Kioto, Kyōto, Japan
  • 1985
    • Nordic Institute for Theoretical Physics
      Tukholma, Stockholm, Sweden