Solving the simplest theory of quantum gravity Dubovsky, Sergei; Flauger, Raphael; Gorbenko, Victor
The journal of high energy physics,
09/2012, Letnik:
2012, Številka:
9
Journal Article
Recenzirano
Odprti dostop
A
bstract
We solve what is quite likely the simplest model of quantum gravity, the worldsheet theory of an infinitely long, free bosonic string in Minkowski space. Contrary to naive expectations, ...this theory is non-trivial. We illustrate this by constructing its exact factorizable S-matrix. Despite its simplicity, the theory exhibits many of the salient features expected from more mature quantum gravity models, including the absence of local off-shell observables, a minimal length, as well as (integrable relatives of) black holes. All these properties follow from the exact
S
-matrix. We show that the complete finite volume spectrum can be reconstructed analytically from this
S
-matrix with the help of the thermodynamic Bethe Ansatz. We argue that considered as a UV complete relativistic 2-dimensional quantum field theory the model exhibits a new type of renormalization group flow behavior, “asymptotic fragility”. Asymptotically fragile flows do not originate from a UV fixed point.
A
bstract
We discuss how scattering amplitudes in 4d Minkowski spacetime which involve multiple soft gravitons realize the algebra of BMS charges on the null boundary. In particular, we show how the ...commutator of two such charges is realized by the antisymmetrized consecutive soft limit of the double soft amplitude. The commutator is expected to be robust even in the presence of quantum corrections, and the associated Lie algebra has an extension, which breaks the BMS symmetry if the BMS algebra is taken to include the Virasoro algebra of local superrotations. We discuss the implications of this structure for the existence of a 2d CFT dual description for 4d scattering amplitudes.
Effective string theory revisited Dubovsky, Sergei; Flauger, Raphael; Gorbenko, Victor
The journal of high energy physics,
09/2012, Letnik:
2012, Številka:
9
Journal Article
Recenzirano
Odprti dostop
A
bstract
We revisit the effective field theory of long relativistic strings such as confining flux tubes in QCD. We derive the Polchinski-Strominger interaction by a calculation in static gauge. ...This interaction implies that a non-critical string which initially oscillates in one direction gets excited in orthogonal directions as well. In static gauge no additional term in the effective action is needed to obtain this effect. It results from a one-loop calculation using the Nambu-Goto action. Non-linearly realized Lorentz symmetry is manifest at all stages in dimensional regularization. We also explain that independent of the number of dimensions non-covariant counterterms have to be added to the action in the commonly used zeta-function regularization.
We propose a new approach for the calculation of the spectrum of excitations of QCD flux tubes. It relies on the fact that the worldsheet theory is integrable at low energies. With this approach, ...energy levels can be calculated for much shorter flux tubes than was previously possible, allowing for a quantitative comparison with existing lattice data. The improved theoretical control makes it manifest that existing lattice data provides strong evidence for a new pseudoscalar particle localized on the QCD flux tube--the worldsheet axion.
We show that simulations of magnetohydrodynamic turbulence in the multiphase interstellar medium yield an E/B ratio for polarized emission from Galactic dust in broad agreement with recent Planck ...measurements. In addition, the B-mode spectra display a scale dependence that is consistent with observations over the range of scales resolved in the simulations. The simulations present an opportunity to understand the physical origin of the E/B ratio and a starting point for more refined models of Galactic emission of use for both current and future cosmic microwave background experiments.
The existence of the cosmic neutrino background is a robust prediction of the hot big bang model. These neutrinos were a dominant component of the energy density in the early Universe and therefore ...played an important role in the evolution of cosmological perturbations. The energy density of the cosmic neutrino background has been measured using the abundances of light elements and the anisotropies of the cosmic microwave background. A complementary and more robust probe is provided by a distinct shift in the temporal phase of sound waves in the primordial plasma that is produced by fluctuations in the neutrino density. Here, we report on the first constraint on this neutrino-induced phase shift in the spectrum of baryon acoustic oscillations of the BOSS DR12 data. Constraining the acoustic scale using Planck data while marginalizing over the effects of neutrinos in the cosmic microwave background, we find a non-zero phase shift at greater than 95% confidence. Besides providing a new test of the cosmic neutrino background, our work is the first application of the baryon acoustic oscillation signal to early Universe physics.In the early Universe, fluctuations in the neutrino density produced a distinct shift in the temporal phase of sound waves in the primordial plasma. The size of this phase shift has now been constrained through baryon acoustic oscillation data.
We present the first large set of all-sky synthetic dust polarization maps derived directly from a self-consistent magnetohydrodynamics simulation using the TIGRESS framework. Turbulence in this ...simulation is predominantly driven by supernova explosions, with rates that are self-consistently regulated by feedback loops. The simulation covers both the outer scale and inertial range of turbulence with uniformly high resolution. The shearing-box utilized in the simulation, in concert with resolved supernova-driven turbulence, enables the capturing of generation, growth, and saturation of both turbulent and mean magnetic fields. We construct polarization maps at 353 GHz, as seen by observers inside a model of the multiphase, turbulent, magnetized interstellar medium (ISM). To fully sample the simulated ISM state, we use 350 snapshots spanning over (more than six feedback loops) and nine representative observers. The synthetic skies show a prevalent E/B power asymmetry ( ) and positive TE correlation in broad agreement with observations by the Planck satellite. However, the ranges of and are generally lower than those measured by Planck. We find large fluctuations of E/B asymmetry and TE correlation depending on the observer's position and temporal fluctuations of ISM properties due to bursts of star formation. The synthetic maps are made publicly available to provide novel models of the microwave sky.
We study the effects of cold dark matter on the propagation of gravitational waves of astrophysical and primordial origin. We show that the dominant effect of cold dark matter on gravitational waves ...from astrophysical sources is a small frequency dependent modification of the propagation speed of gravitational waves. However, the magnitude of the effect is too small to be detected in the near future. We furthermore show that the spectrum of primordial gravitational waves in principle contains detailed information about the properties of dark matter. However, depending on the wavelength, the effects are either suppressed because the dark matter is highly nonrelativistic or because it contributes a small fraction of the energy density of the universe. As a consequence, the effects of cold dark matter on primordial gravitational waves in practice also appear too small to be detectable.
The rate of gravitational wave absorption by inverse bremsstrahlung is calculated. It increases with decreasing frequency ν as ν−3. Nevertheless, because of the near cancellation of absorption by ...stimulated emission, the ionized gas in galaxy clusters does not block gravitational waves at the nanohertz frequencies that may be detected by the use of pulsar timing observations.
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