144 research outputs found
Consequences of Symmetries and Consistency Relations in the Large-Scale Structure of the Universe for Non-local bias and Modified Gravity
Consistency relations involving the soft limit of the (n + 1)-correlator
functions of dark matter and galaxy overdensities can be obtained, both in real
and redshift space, thanks to the symmetries enjoyed by the Newtonian equations
of motion describing the dark matter and galaxy fluids coupled through gravity.
We study the implications of such symmetries for the theory of galaxy bias and
for the theories of modified gravity. We find that the invariance of the fluid
equations under a coordinate transformation that induces a long-wavelength
velocity constrain the bias to depend only on a set of invariants, while the
symmetry of such equations under Lifshitz scalings in the case of matter
domination allows one to compute the time-dependence of the coefficients in the
bias expansion. We also find that in theories of modified gravity which violate
the equivalence principle induce a violation of the consistency relation which
may be a signature for their observation. Thus, given adiabatic Gaussian
initial conditions, the observation of a deviation from the consistency
relation for galaxies would signal a break-down of the so-called non-local
Eulerian bias model or the violation of the equivalence principle in the
underlying theory of gravity.Comment: 29 pages, 1 figur
Resilience of the standard predictions for primordial tensor modes
We show that the prediction for the primordial tensor power spectrum cannot
be modified at leading order in derivatives. Indeed, one can always set to
unity the speed of propagation of gravitational waves during inflation by a
suitable disformal transformation of the metric, while a conformal one can make
the Planck mass time-independent. Therefore, the tensor amplitude unambiguously
fixes the energy scale of inflation. Using the Effective Field Theory of
Inflation, we check that predictions are independent of the choice of frame, as
expected. The first corrections to the standard prediction come from two parity
violating operators with three derivatives. Also the correlator
is standard and only receives higher derivative
corrections. These results hold also in multifield models of inflation and in
alternatives to inflation and make the connection between a (quasi)
scale-invariant tensor spectrum and inflation completely robust.Comment: 5 pages, reference added, version accepted in PR
Spherical collapse in quintessence models with zero speed of sound
We study the spherical collapse model in the presence of quintessence with
negligible speed of sound. This case is particularly motivated for w<-1 as it
is required by stability. As pressure gradients are negligible, quintessence
follows dark matter during the collapse. The spherical overdensity behaves as a
separate closed FLRW universe, so that its evolution can be studied exactly. We
derive the critical overdensity for collapse and we use the extended
Press-Schechter theory to study how the clustering of quintessence affects the
dark matter mass function. The effect is dominated by the modification of the
linear dark matter growth function. A larger effect occurs on the total mass
function, which includes the quintessence overdensities. Indeed, here
quintessence constitutes a third component of virialized objects, together with
baryons and dark matter, and contributes to the total halo mass by a fraction ~
(1+w) Omega_Q / Omega_m. This gives a distinctive modification of the total
mass function at low redshift.Comment: 38 pages; small changes, including modification of the window
function. JCAP published versio
Dark matter and halo bispectrum in redshift space: theory and applications
We present a phenomenological modification of the standard perturbation
theory prediction for the bispectrum in redshift space that allows us to extend
the model to mildly non-linear scales over a wide range of redshifts,
. We find that we can describe the bispectrum of dark matter
particles with accuracy for at ,
for at , for at and for at . We also
test that the fitting formula is able to describe with similar accuracy the
bispectrum of cosmologies with different , in the range , and consequently with different values of the
logarithmic grow rate at , . We apply
this new formula to recover the bias parameters, and , by
combining the redshift space power spectrum monopole and quadrupole with the
bispectrum monopole for both dark matter particles and haloes. We find that the
combination of these three statistics can break the degeneracy between ,
and . For dark matter particles the new model can be used to
recover and with accuracy. For dark matter haloes we
find that and present larger systematic shifts, . The
systematic offsets arise because of limitations in the modelling of the
interplay between bias and redshift space distortions, and represent a
limitation as the statistical errors of forthcoming surveys reach this level.
Conveniently, we find that these residual systematics are mitigated for
combinations of parameters. The improvement on the modelling of the bispectrum
presented in this paper will be useful for extracting information from current
and future galaxy surveys. [abridged]Comment: 37 pages, 17 figures, 8 tables. Published in JCA
Fermion mass hierarchy and non-hierarchical mass ratios in SU(5) x U(1)_F
We consider a SU(5) x U(1)_F GUT-flavor model in which the number of effects
that determine the charged fermions Yukawa matrices is much larger than the
number of observables, resulting in a hierarchical fermion spectrum with no
particular regularities. The GUT-flavor symmetry is broken by flavons in the
adjoint of SU(5), realizing a variant of the Froggatt-Nielsen mechanism that
gives rise to a large number of effective operators. By assuming a common mass
for the heavy fields and universality of the fundamental Yukawa couplings, we
reduce the number of free parameters to one. The observed fermion mass spectrum
is reproduced thanks to selection rules that discriminate among various
contributions. Bottom-tau Yukawa unification is preserved at leading order, but
there is no unification for the first two families. Interestingly, U(1)_F
charges alone do not determine the hierarchy, and can only give upper bounds on
the parametric suppression of the Yukawa operators.Comment: 14 pages, one figure. Few typos correcte
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