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Sep 19, 2013
09/13

by
A. Riotto

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In these lectures the present status of the so-called standard cosmological model, based on the hot Big Bang theory and the inflationary paradigm is reviewed. Special emphasis is given to the origin of the cosmological perturbations we see today under the form of the cosmic microwave background anisotropies and the large scale structure and to the dark matter and dark energy puzzles.

Source: http://arxiv.org/abs/1010.2642v1

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Sep 20, 2013
09/13

by
A. Riotto

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We discuss some recent developments made in the computation of the baryon asymmetry generated at the electroweak scale. We emphasize that the local number density asymmetries of the particles involved in supersymmetric electroweak baryogenesis must be described by a set of Quantum Boltzmann Equations. These diffusion equations automatically and self-consistently incorporate the CP-violating sources which fuel baryogenesis and manifest ``memory'' effects which are typical of the quantum...

Source: http://arxiv.org/abs/hep-ph/9802240v1

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Sep 18, 2013
09/13

by
G. Dvali; A. Riotto

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Usually one expectes the inflaton field to be coupled to some gauge-charged particles allowing for its decay during reheating. Such particles then play a role of the messengers for the gauge-mediated supersymmetry breaking during and (shortly) after the inflation and radiatively induce soft masses to all other $D$-flat directions. We show that during the preheating stage this gauge-mediated soft masses are typically much greater than the Hubble parameter during inflation. The dramatic role is...

Source: http://arxiv.org/abs/hep-ph/9606431v1

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Jul 22, 2013
07/13

by
G. Ballesteros; A. Riotto

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We present an analytical fit to the growth function of the dark matter perturbations when dark energy perturbations are present. The growth index depends upon the dark energy equation of state w, the speed of sound of the dark energy fluctuations, the dark matter abundance and the observed comoving scale. The growth index changes by ~5% for small speed of sound and large deviations of w from -1 with respect to its value in the limit of no dark energy perturbations.

Source: http://arxiv.org/abs/0807.3343v3

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Sep 20, 2013
09/13

by
A. Kehagias; A. Riotto

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We study the multifield inflationary models where the cosmological perturbation is sourced by light scalar fields other than the inflaton. The corresponding perturbations are both scale invariant and special conformally invariant. We exploit the operator product expansion technique of conformal field theories to study the inflationary correlators enjoying the symmetries present during the de Sitter epoch. The operator product expansion is particularly powerful in characterizing inflationary...

Source: http://arxiv.org/abs/1205.1523v1

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52

Sep 22, 2013
09/13

by
A. Kehagias; A. Riotto

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We study the multifield inflationary models where the cosmological perturbation is sourced by light scalar fields other than the inflaton. We exploit the operator product expansion and partly the symmetries present during the de Sitter epoch to characterize the non-Gaussian four-point correlator in the squeezed limit. We point out that the contribution to it from the intrinsic non-Gaussianity of the light fields at horizon crossing can be larger than the usually studied contribution arising on...

Source: http://arxiv.org/abs/1210.1918v1

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54

Sep 19, 2013
09/13

by
F. Illuminati; A. Riotto

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We investigate the role played by subcritical bubbles at the onset of the electroweak phase transition. Treating the configuration modelling the thermal fluctuations around the homogeneous zero configuration of the Higgs field as a stochastic variable, we describe its dynamics by a phenomenological Langevin equation. This approach allows to properly take into account both the effects of the thermal bath on the system: a systematic dyssipative force, which tends to erase out any initial...

Source: http://arxiv.org/abs/hep-ph/9506419v1

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88

Sep 17, 2013
09/13

by
N. Bartolo; A. Riotto

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We point out that the theoretical predictions for the inflationary observables may be generically altered by the presence of fields which are heavier than the Hubble rate during inflation and whose dynamics is usually neglected. They introduce corrections which may be easily larger than both the second-order contributions in the slow-roll parameters and the accuracy expected in the forthcoming experiments.

Source: http://arxiv.org/abs/0711.4003v1

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37

Sep 22, 2013
09/13

by
A. Kehagias; A. Riotto

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We study the symmetries enjoyed by the Newtonian equations of motion of the non-relativistic dark matter fluid coupled to gravity which give rise to the phenomenon of gravitational instability. We also discuss some consistency relations involving the soft limit of the (n + 1)-correlator functions of matter and galaxy overdensities.

Source: http://arxiv.org/abs/1302.0130v1

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Sep 23, 2013
09/13

by
A. Riotto; E. Roulet

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It has been recently realized that within the Minimal Supersymmetric Standard Model, for certain patterns of superpartner masses, consistent with all the present experimental constraints, the scalar potential may develop at some scale $Q_0$ unbounded color/charge breaking directions involving the sfermion fields, and that these patterns are then excluded unless some new physics is invoked at or below the scale $Q_0$. We reanalyze this observation and point out that such patterns of superpartner...

Source: http://arxiv.org/abs/hep-ph/9512401v1

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37

Sep 19, 2013
09/13

by
R. Brandenberger; A. Riotto

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A generic prediction of models where supersymmetry is broken at scales within a few orders of magnitude of the weak scale and is fed down to the observable sector by gauge interactions is the existence of superconducting cosmic strings which carry baryon number. In this paper we propose a novel mechanism for the generation of the baryon asymmetry which takes place at temperatures much lower than the weak scale. Superconducting strings act like ``bags'' containing the baryon charge and protect...

Source: http://arxiv.org/abs/hep-ph/9801448v2

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62

Sep 21, 2013
09/13

by
H. Lew; A. Riotto

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It has been recently speculated that global symmetries are broken by gravity. We propose a scenario for the generation of the baryon asymmetry in the early Universe in which the domain walls predicted by theories with discrete symmetries become unstable due to these Planck scale effects. The relative motion of the decaying walls can provide a mechanism for the departure from thermal equilibrium necessary to have a nonvanishing baryon asymmetry. In particular, we implement this idea within the...

Source: http://arxiv.org/abs/hep-ph/9304203v1

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Sep 22, 2013
09/13

by
H. Lew; A. Riotto

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A scenario for the generation of the baryon asymmetry in the early Universe is proposed in which cosmic string loops, predicted by theories where the baryon and/or lepton numbers are gauged symmetries, collapse during the friction dominated period of string evolution. This provides a mechanism for the departure from thermal equilibrium necessary to have a nonvanishing baryon asymmetry. Examples of models are given where this idea can be implemented. In particular, the model with the gauge...

Source: http://arxiv.org/abs/hep-ph/9306336v1

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60

Sep 22, 2013
09/13

by
A. Notari; A. Riotto

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The Ekpyrotic scenario assumes that our visible Universe is a boundary brane in a five-dimensional bulk and that the hot Big Bang occurs when a nearly supersymmetric five-brane travelling along the fifth dimension collides with our visible brane. We show that the generation of isocurvature perturbations is a generic prediction of the Ekpyrotic Universe. This is due to the interactions in the kinetic terms between the brane modulus parametrizing the position of the five-brane in the bulk and the...

Source: http://arxiv.org/abs/hep-th/0205019v2

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64

Sep 21, 2013
09/13

by
M. Liguori; A. Riotto

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We study the impact of cosmological parameters' uncertainties on estimates of the primordial NG parameter f_NL in local and equilateral models of non-Gaussianity. We show that propagating these errors increases the f_NL relative uncertainty by 16% for WMAP and 5 % for Planck in the local case, whereas for equilateral configurations the correction term are 14% and 4%, respectively. If we assume for local f_NL a central value of order 60, according to recent WMAP 5-years estimates, we obtain for...

Source: http://arxiv.org/abs/0808.3255v1

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80

Sep 18, 2013
09/13

by
A. Riotto; I. Vilja

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Nonequilibrium phenomena of the phase transitions are studied. It is shown that due to finite relaxation time of the particle distributions, the use of scalar background dependent distribution functions is inconsistent.This observation may change the picture of rapid processes during the electroweak phase transition, like subcritical bubble formation and propagation of bubble walls.

Source: http://arxiv.org/abs/hep-ph/9509252v1

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91

Sep 18, 2013
09/13

by
A. Riotto; L. Scarabello

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We consider a five-dimensional brane world scenario where the fifth dimension is compactified on $S^1/Z_2$. We show that the familiar four-dimensional cosmology on our brane is easily recovered during a primordial stage of inflation if supersymmetry is exploited. Even if some vacuum energy density appears localized on our three brane, heavy supersymmetric bulk fields adjust themselves and acquire a nontrivial configuration along the extra-dimension. This phenomenon redistributes uniformly the...

Source: http://arxiv.org/abs/hep-ph/0110234v1

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Sep 22, 2013
09/13

by
D. H. Lyth; A. Riotto

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An inflationary stage dominated by a D-term avoids the slow-roll problem of inflation in supergravity and can naturally emerge in theories with a non-anomalous or anomalous U(1) gauge symmetry. In the latter case, however, the scale of inflation as imposed by the COBE normalization is in contrast with the value fixed by the Green-Schwarz mechanism of anomaly cancellation. In this paper we discuss possible solutions to this problem and comment about the fact that the string-loop generated...

Source: http://arxiv.org/abs/hep-ph/9707273v1

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53

Sep 21, 2013
09/13

by
R. N. Mohapatra; A. Riotto

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We show that a recently proposed extension of the MSSM can provide a scenario where both the cold and hot dark matter of the universe owe their origin to a single scale connected with the breakdown of the global B-L symmetry. The susy partner of the majoron and the light Majorana neutrinos are the cold and hot dark matter candidates respectively in this model and their desired relative abundances emerge when the scale of B-L symmetry breaking is in the TeV range.

Source: http://arxiv.org/abs/hep-ph/9403275v1

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43

Sep 20, 2013
09/13

by
D. H. Lyth; A. Riotto

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In brane inflationary scenarios, the cosmological perturbations are supposed to originate from the vacuum fluctuations of the inflaton field corresponding to the position of the brane. We show that a significant, and possibly dominant, contribution to the curvature perturbation is generated at the end of inflation through the vacuum fluctuations of fields, other than the inflaton, which are light during the inflationary trajectory and become heavy at the brane-anti brane annihilation. These...

Source: http://arxiv.org/abs/astro-ph/0607326v1

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48

Sep 20, 2013
09/13

by
R. N. Mohapatra; A. Riotto

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We construct realistic supergravity models where supersymmetry breaking arises from the D-terms of an anomalous U(1) gauge symmetry broken at the Planck scale. Effective action for these theories at sub-Planck energies (including higher dimensional terms in the superpotential) are severely restricted by the U(1) symmetry and by the assumption that they arise from an underlying renormalizable theory at a higher scale. Phenomenological consequences of these models are studied. They are found to...

Source: http://arxiv.org/abs/hep-ph/9611273v1

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50

Sep 18, 2013
09/13

by
A. Riotto; I. I. Tkachev

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We calculate the strength of symmetry restoration effects in highly non-equilibrium states which can arise, for example, during preheating after inflation. We show that in certain parameter range the one-loop results are unstable, requiring summation of multiloop diagrams. We solve this problem for the $O(N)$ model in the large $N$-limit and show that the symmetry restoration may be less effective than what predicted by the one-loop estimate.

Source: http://arxiv.org/abs/hep-ph/9604444v1

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50

Sep 23, 2013
09/13

by
S. F. King; A. Riotto

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Dilaton stabilisation is usually considered to pose a serious obstacle to successful $D$-term inflation in superstring theories. We argue that the physics of gaugino condensation is likely to be modified during the inflationary phase in such a way as to enhance the gaugino condensation scale. This enables dilaton stabilisation during inflation with the $D$-term still dominating the vacuum energy at the stable minimum.

Source: http://arxiv.org/abs/hep-ph/9806281v1

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53

Sep 18, 2013
09/13

by
D. Comelli; M. Pietroni; A. Riotto

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We compute the particle currents induced on a bubble wall background at finite temperature in a model with CP violation in the Higgs sector. Using a field theory approach we show that fermionic currents arise at one loop, so that a suppression factor ${\cal O}(h_t \phi/\pi T)^2$ with respect to previous computations is found. The contributions to the Higgs currents are also derived and their relevancy for the spontaneous baryogenesis mechanism is discussed.

Source: http://arxiv.org/abs/hep-ph/9504265v1

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47

Sep 22, 2013
09/13

by
N. Bartolo; S. Matarrese; A. Riotto

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We discuss how primordial (e.g. inflationary) non-Gaussianity in the cosmological perturbations is left imprinted in the Large-Scale Structure of the universe. Our findings show that the information on the primordial non-Gaussianity set on super-Hubble scales flows into Post-Newtonian terms, leaving an observable imprint in the Large-Scale Structure. Future high-precision measurements of the statistics of the dark matter density and peculiar velocity fields will allow to pin down the primordial...

Source: http://arxiv.org/abs/astro-ph/0501614v2

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133

Sep 19, 2013
09/13

by
D. Comelli; M. Pietroni; A. Riotto

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It is a puzzle why the densities of dark matter and dark energy are nearly equal today when they scale so differently during the expansion of the universe. This conundrum may be solved if there is a coupling between the two dark sectors. In this paper we assume that dark matter is made of cold relics with masses depending exponentially on the scalar field associated to dark energy. Since the dynamics of the system is dominated by an attractor solution, the dark matter particle mass is forced to...

Source: http://arxiv.org/abs/hep-ph/0302080v1

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57

Sep 22, 2013
09/13

by
K. Enqvist; A. Riotto; I. Vilja

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We consider the role played by subcritical bubbles during the electroweak phase transition, estimate their average size, amplitude and formation rate taking into account the crucial role played by thermalization. We also study the influence of subcritical bubbles on the formation of critical bubbles in the thin wall regime and show that, contrary to some recent claims, subcritical bubbles do not affect the nucleation of critical bubbles in an appreciable way. From this fact we conclude that the...

Source: http://arxiv.org/abs/hep-ph/9505341v1

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45

Sep 19, 2013
09/13

by
N. Fornengo; A. Riotto; S. Scopel

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Since the thermal history of the Universe is unknown before the epoch of primordial nucleosynthesis, the largest temperature of the radiation dominated phase (the reheating temperature) might have been as low as 1 MeV. We perform a quantitative study of supersymmetric dark matter relic abundance in cosmological scenarios with low reheating temperature. We show that, for values of the reheating temperature smaller than about 30 GeV, the domains of the supergravity parameter space which are...

Source: http://arxiv.org/abs/hep-ph/0208072v1

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48

Sep 19, 2013
09/13

by
D. Comelli; M. Pietroni; A. Riotto

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Motivated by cosmological applications like electroweak baryogenesis, we develop a field theoretic approach to the computation of particle currents on a space-time dependent and CP-violating Higgs background. We consider the Standard Model model with two Higgs doublets and CP violation in the scalar sector, and compute both fermionic and Higgs currents by means of an expansion in the background fields. We discuss the gauge dependence of the results and the renormalization of the current...

Source: http://arxiv.org/abs/hep-ph/9506278v2

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49

Sep 22, 2013
09/13

by
N. Bartolo; S. Matarrese; A. Riotto

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We present a second-order gauge-invariant formalism to study the evolution of curvature perturbations in a Friedmann-Robertson-Walker universe filled by multiple interacting fluids. We apply such a general formalism to describe the evolution of the second-order curvature perturbations in the standard one-single field inflation, in the curvaton and in the inhomogeneous reheating scenarios for the generation of the cosmological perturbations. Moreover, we provide the exact expression for the...

Source: http://arxiv.org/abs/astro-ph/0309692v3

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68

Sep 23, 2013
09/13

by
D. Comelli; M. Pietroni; A. Riotto

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The spontaneous baryogenesis mechanism by Cohen, Kaplan and Nelson is reconsidered taking into account the transport of particles inside the electroweak bubble walls. Using linear response theory, we calculate the modifications on the thermal averages of the charges of the system due to the presence of a space time dependent `charge potential' for a quantum number not orthogonal to baryon number. The local equilibrium configuration is discussed, showing that, as a consequence of non zero...

Source: http://arxiv.org/abs/hep-ph/9406369v1

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47

Sep 22, 2013
09/13

by
N. Bartolo; S. Matarrese; A. Riotto

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We study the evolution of cosmological perturbations on large scales, up to second order, for a perfect fluid with generic equation of state. Taking advantage of super-horizon conservation laws, it is possible to follow the evolution of the non-Gaussianity of perturbations through the different stages after inflation. We find that a large non-linearity is generated by the gravitational dynamics from the original inflationary quantum fluctuations. This leads to a significant enhancement of the...

Source: http://arxiv.org/abs/astro-ph/0308088v4

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65

Jul 20, 2013
07/13

by
N. Bartolo; S. Matarrese; A. Riotto

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We study adiabatic and isocurvature perturbations produced during a period of cosmological inflation. We compute the power spectra and cross spectra of the curvature and isocurvature modes, as well as the tensor perturbation spectrum in terms of the slow-roll parameters. We provide two consistency relations for the amplitudes and spectral indices of the corresponding power spectra. These relations represent a definite prediction and a test of inflationary models which should be adopted when...

Source: http://arxiv.org/abs/astro-ph/0107502v1

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145

Jul 20, 2013
07/13

by
N. Bartolo; S. Matarrese; A. Riotto

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We present the computation of the full system of Boltzmann equations at second-order describing the evolution of the photon, baryon and cold dark matter fluids. These equations allow to follow the time evolution of the Cosmic Microwave Background (CMB) anisotropies at second-order at all angular scales from the early epoch, when the cosmological perturbations were generated, to the present through the recombination era. This paper sets the stage for the computation of the full second-order...

Source: http://arxiv.org/abs/astro-ph/0604416v4

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65

Sep 18, 2013
09/13

by
L. Pilo; A. Riotto; A. Zaffaroni

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We propose a stringy version of the old inflation scenario which does not require any slow-roll inflaton potential and is based on a specific example of string compatification with warped metric. Our set-up admits the presence of anti-D3-branes in the deep infrared region of the metric and a false vacuum state with positive vacuum energy density. The latter is responsible for the accelerated period of inflation. The false vacuum exists only if the number of anti-D3-branes is smaller than a...

Source: http://arxiv.org/abs/hep-th/0401004v2

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54

Sep 23, 2013
09/13

by
A. Riotto; E. Roulet; I. Vilja

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The constraints imposed by the requirement that the scalar potential of supersymmetric theories does not have unbounded directions and charge or color breaking minima deeper than the usual electroweak breaking minimum (EWM) are significantly relaxed if one just allows for a metastable EWM but with a sufficiently long lifetime. For this to be acceptable one needs however to explain how the vacuum state reaches this metastable configuration in the first place. We discuss the implications for this...

Source: http://arxiv.org/abs/hep-ph/9607403v1

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50

Sep 22, 2013
09/13

by
D. Comelli; M. Pietroni; A. Riotto

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We study the implications of a light stop for the spontaneous CP breaking at finite temperature in the Higgs sector of the Minimal Supersymmetric Standard Model with a gauge singlet. Assuming CP conservation at zero temperature, we show that the presence of a large mixing between the left- and the right-handed stops can trigger easily the spontaneous breaking of CP inside the bubbles nucleated during the electroweak phase transition. This allows to avoid the fine-tuning among the vacuum...

Source: http://arxiv.org/abs/hep-ph/9410225v1

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66

Sep 23, 2013
09/13

by
N. Bartolo; S. Matarrese; A. Riotto

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We estimate analytically the second-order cosmic microwave background temperature anisotropies at the recombination epoch in the squeezed limit and we deduce the contamination to the primordial local non-Gaussianity. We find that the level of contamination corresponds to f_NL^{con}=O(1) which is below the sensitivity of present experiments and smaller than the value O(5) recently claimed in the literature.

Source: http://arxiv.org/abs/1109.2043v2

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Jun 30, 2018
06/18

by
P. Berger; A. Kehagias; A. Riotto

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We study the symmetries of the post-recombination cosmological magnetohydrodynamical equations which describe the evolution of dark matter, baryons and magnetic fields in a self-consistent way. This is done both at the level of fluid equations and of Vlasov-Poisson-Maxwell equations in phase space. We discuss some consistency relations for the soft limit of the (n + 1)-correlator functions involving magnetic fields and matter overdensities. In particular, we stress that any violation of such...

Topics: High Energy Physics - Theory, High Energy Physics - Phenomenology, Astrophysics, General Relativity...

Source: http://arxiv.org/abs/1402.1044

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81

Sep 22, 2013
09/13

by
N. Bartolo; S. Matarrese; A. Riotto

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Adiabatic (curvature) perturbations are produced during a period of cosmological inflation that is driven by a single scalar field, the inflaton. On particle physics grounds -- though -- it is natural to expect that this scalar field is coupled to other scalar degrees of freedom. This gives rise to oscillations between the perturbation of the inflaton field and the perturbations of the other scalar degrees of freedom, similar to the phenomenon of neutrino oscillations. Since the degree of the...

Source: http://arxiv.org/abs/astro-ph/0106022v2

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53

Sep 22, 2013
09/13

by
N. Bartolo; S. Matarrese; A. Riotto

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Since a positive future detection of non-linearity in the cosmic microwave background anisotropy pattern might allow to descriminate among different mechanisms giving rise to cosmological adiabatic perturbations, we study the evolution of the second-order cosmological curvature perturbation on super-horizon scales in the curvaton scenario. We provide the exact expression for the non-Gaussianity in the primordial perturbations including gravitational second-order corrections which are...

Source: http://arxiv.org/abs/hep-ph/0309033v3

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42

Sep 23, 2013
09/13

by
D. Comelli; M. Pietroni; A. Riotto

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We study the spontaneous CP breaking at finite temperature in the Higgs sector in the Minimal Supersymmetric Standard Model with a gauge singlet. We consider the contribution of the standard model particles and that of stops, charginos, neutralinos, charged and neutral Higgs boson to the one-loop effective potential. Plasma effects for all bosons are also included. Assuming CP conservation at zero temperature, so that experimental constraints coming from, {\it e.g.}, the electric dipole moment...

Source: http://arxiv.org/abs/hep-ph/9406368v1

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Sep 18, 2013
09/13

by
L. Pilo; A. Riotto; A. Zaffaroni

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The curvaton and the inhomogeneous reheating scenarios for the generation of the cosmological curvature perturbation on large scales represent an alternative to the standard slow-roll scenario where the observed density perturbations are due to fluctuations of the inflaton field itself. The basic assumption of the curvaton and inhomogeneous reheating mechanisms is that the initial curvature perturbation due to the inflaton field is negligible. This is usually attained by lowering the energy...

Source: http://arxiv.org/abs/astro-ph/0401302v1

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50

Sep 20, 2013
09/13

by
N. Bartolo; S. Matarrese; A. Riotto

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We compute the fully non-linear Cosmic Microwave Background (CMB) anisotropies on scales larger than the horizon at last-scattering in terms of only the curvature perturbation, providing a generalization of the linear Sachs-Wolfe effect at any order in perturbation theory. We show how to compute the n-point connected correlation functions of the large-scale CMB anisotropies for generic primordial seeds provided by standard slow-roll inflation as well as the curvaton and other scenarios for the...

Source: http://arxiv.org/abs/astro-ph/0506410v2

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51

Sep 21, 2013
09/13

by
N. Bartolo; S. Matarrese; A. Riotto

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When dealing with observables, one needs to generalize the bias relation between the observed galaxy fluctuation field to the underlying matter distribution in a gauge-invariant way. We provide such relation at second-order in perturbation theory adopting the local Eulerian bias model and starting from the observationally motivated uniform-redshift gauge. Our computation includes the presence of primordial non-Gaussianity. We show that large scale-dependent relativistic effects in the Eulerian...

Source: http://arxiv.org/abs/1011.4374v2

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68

Sep 22, 2013
09/13

by
N. Bartolo; S. Matarrese; A. Riotto

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We review in a pedagogical way the present status of the impact of non-Gaussianity (NG) on the Cosmic Microwave Background (CMB) anisotropies. We first show how to set the initial conditions at second-order for the (gauge invariant) CMB anisotropies when some primordial NG is present. However, there are many sources of NG in CMB anisotropies, beyond the primordial one, which can contaminate the primordial signal. We mainly focus on the NG generated from the post-inflationary evolution of the...

Source: http://arxiv.org/abs/1001.3957v1

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Sep 21, 2013
09/13

by
N. Bartolo; S. Matarrese; A. Riotto

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We provide the gauge-invariant expression for large-scale cosmic microwave background temperature fluctuations at second-order in perturbation theory. It enables to unambiguously define the nonlinearity parameter f_NL which is used by experimental collaborations to pin down the level of Non-Gaussianity in the temperature fluctuations. Furthermore, it contains a primordial term encoding all the information about the Non-Gaussianity generated at primordial epochs and about the mechanism which...

Source: http://arxiv.org/abs/astro-ph/0407505v2

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Sep 22, 2013
09/13

by
G. v. Gersdorff; M. Quiros; A. Riotto

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We study the issue of radion stabilization within five-dimensional supersymmetric theories compactified on the orbifold S^1/Z_2. We break supersymmetry by the Scherk-Schwarz mechanism and explain its implementation in the off-shell formulation of five dimensional supergravity in terms of the tensor and linear compensator multiplets. We show that radion stabilization may be achieved by radiative corrections in the presence of five-dimensional fields which are quasi-localized on the boundaries...

Source: http://arxiv.org/abs/hep-th/0310190v1

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Sep 20, 2013
09/13

by
E. W. Kolb; S. Matarrese; A. Riotto

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We elaborate on the proposal that the observed acceleration of the Universe is the result of the backreaction of cosmological perturbations, rather than the effect of a negative-pressure dark-energy fluid or a modification of general relativity. Through the effective Friedmann equations describing an inhomogeneous Universe after smoothing, we demonstrate that acceleration in our local Hubble patch is possible even if fluid elements do not individually undergo accelerated expansion. This...

Source: http://arxiv.org/abs/astro-ph/0506534v2

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Sep 19, 2013
09/13

by
N. Bartolo; Edward W. Kolb; A. Riotto

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We investigate the possibility that the amplitude of scalar density perturbations may be damped after inflation. This would imply that CMB anisotropies do not uniquely fix the amplitude of the perturbations generated during inflation and that the present tensor-to-scalar ratio might be larger than produced in inflation, increasing the prospects of detection of primordial gravitational radiation. It turns out, however, that the damping of density perturbations is hard to achieve.

Source: http://arxiv.org/abs/astro-ph/0507573v3