240 research outputs found
Localization on the Landscape and Eternal Inflation
We investigate the validity of the assertion that eternal inflation populates
the landscape of string theory. We verify that bubble solutions do not satisfy
the Klein Gordon equation for the landscape potential. Solutions to the
landscape potential within the formalism of quantum cosmology are Anderson
localized wavefunctions. Those are inconsistent with inflating bubble
solutions. The physical reasons behind the failure of a relation between
eternal inflation and the landscape are rooted in quantum phenomena such as
interference between wavefunction concentrated around the various vacua in the
landscape.Comment: 21 page
Cosmic bubble and domain wall instabilities III: The role of oscillons in three-dimensional bubble collisions
We study collisions between pairs of bubbles nucleated in an ambient false
vacuum. For the first time, we include the effects of small initial (quantum)
fluctuations around the instanton profiles describing the most likely initial
bubble profile. Past studies of this problem neglect these fluctuations and
work under the assumption that the collisions posess an exact SO(2,1) symmetry.
We use three-dimensional lattice simulations to demonstrate that for
double-well potentials, small initial perturbations to this symmetry can be
amplified as the system evolves. Initially the amplification is well-described
by linear perturbation theory around the SO(2,1) background, but the onset of
strong nonlinearities amongst the fluctuations quickly leads to a drastic
breaking of the original SO(2,1) symmetry and the production of oscillons in
the collision region. We explore several single-field models, and we find it is
hard to both realize inflation inside of a bubble and produce oscillons in a
collision. Finally, we extend our results to a simple two-field model. The
additional freedom allowed by the second field allows us to construct viable
inflationary models that allow oscillon production in collisions. The breaking
of the SO(2,1) symmetry allows for a new class of observational signatures from
bubble collisions that do not posess azimuthal symmetry, including the
production of gravitational waves which cannot be supported by an SO(2,1)
spacetime.Comment: 35 pages + references, 26 figures. Submitted to JCAP. v2:
Acknowledgments updates, no other change
Cosmic bubble and domain wall instabilities II: Fracturing of colliding walls
We study collisions between nearly planar domain walls including the effects
of small initial nonplanar fluctuations. These perturbations represent the
small fluctuations that must exist in a quantum treatment of the problem. In a
previous paper, we demonstrated that at the linear level a subset of these
fluctuations experience parametric amplification as a result of their coupling
to the planar symmetric background. Here we study the full three-dimensional
nonlinear dynamics using lattice simulations, including both the early time
regime when the fluctuations are well described by linear perturbation theory
as well as the subsequent stage of fully nonlinear evolution. We find that the
nonplanar fluctuations have a dramatic effect on the overall evolution of the
system. Specifically, once these fluctuations begin to interact nonlinearly the
split into a planar symmetric part of the field and the nonplanar fluctuations
loses its utility. At this point the colliding domain walls dissolve, with the
endpoint of this being the creation of a population of oscillons in the
collision region. The original (nearly) planar symmetry has been completely
destroyed at this point and an accurate study of the system requires the full
three-dimensional simulation.Comment: 23 pages + references, 13 figures. Submitted to JCAP. v2:
Acknowledgements updated, no other change
Cosmic bubble and domain wall instabilities I: parametric amplification of linear fluctuations
This is the first paper in a series where we study collisions of nucleated
bubbles taking into account the effects of small initial (quantum) fluctuations
in a fully 3+1-dimensional setting. In this paper, we consider the evolution of
linear fluctuations around highly symmetric though inhomogeneous backgrounds.
We demonstrate that a large degree of asymmetry develops over time from tiny
fluctuations superposed upon planar and SO(2,1) symmetric backgrounds. These
fluctuations arise from zero-point vacuum oscillations, so excluding them by
enforcing a spatial symmetry is inconsistent in a quantum treatment. We
consider the limit of two colliding planar walls, with fluctuation mode
functions characterized by the wavenumber transverse to the collision direction
and a longitudinal shape along the collision direction , which we solve for.
Initially, the fluctuations obey a linear wave equation with a time- and
space-dependent mass . When the walls collide multiple times,
oscillates in time. We use Floquet theory to study the fluctuations
and generalize techniques familiar from preheating to the case with many
coupled degrees of freedom. This inhomogeneous case has bands of unstable
transverse wavenumbers with exponentially growing mode functions.
From the detailed spatial structure of the mode functions in , we identify
both broad and narrow parametric resonance generalizations of the homogeneous
case of preheating. The unstable modes are
longitudinally localized, yet can be described as quasiparticles in the
Bogoliubov sense. We define an effective occupation number to show they are
created in bursts for the case of well-defined collisions in the background.
The transverse-longitudinal coupling accompanying nonlinearity radically breaks
this localized particle description, with nonseparable 3D modes arising.Comment: 37 pages + references, 20 figures, submitted to JCA
The KMOS Cluster Survey (KCS). I. The Fundamental Plane and the Formation Ages of Cluster Galaxies at Redshift 1.4 < Z < 1.6
We present the analysis of the fundamental plane (FP) for a sample of 19 massive red-sequence galaxies ( ) in three known overdensities at from the K-band Multi-object Spectrograph (KMOS) Cluster Survey, a guaranteed-time program with spectroscopy from the KMOS at the VLT and imaging from the Hubble Space Telescope. As expected, we find that the FP zero-point in B band evolves with redshift, from the value 0.443 of Coma to −0.10 ± 0.09, −0.19 ± 0.05, and −0.29 ± 0.12 for our clusters at z = 1.39, z = 1.46, and z = 1.61, respectively. For the most massive galaxies () in our sample, we translate the FP zero-point evolution into a mass-to-light-ratio M/L evolution, finding , , to , respectively. We assess the potential contribution of the galaxy structural and stellar velocity dispersion evolution to the evolution of the FP zero-point and find it to be ~6%–35% of the FP zero-point evolution. The rate of M/L evolution is consistent with galaxies evolving passively. Using single stellar population models, we find an average age of Gyr for the galaxies in our massive and virialized cluster at z = 1.39, Gyr in a massive but not virialized cluster at z = 1.46, and Gyr in a protocluster at z = 1.61. After accounting for the difference in the age of the universe between redshifts, the ages of the galaxies in the three overdensities are consistent within the errors, with possibly a weak suggestion that galaxies in the most evolved structure are older
What Can WMAP Tell Us About The Very Early Universe? New Physics as an Explanation of Suppressed Large Scale Power and Running Spectral Index
The Wilkinson Microwave Anisotropy Probe microwave background data may be
giving us clues about new physics at the transition from a ``stringy'' epoch of
the universe to the standard Friedmann Robertson Walker description. Deviations
on large angular scales of the data, as compared to theoretical expectations,
as well as running of the spectral index of density perturbations, can be
explained by new physics whose scale is set by the height of an inflationary
potential. As examples of possible signatures for this new physics, we study
the cosmic microwave background spectrum for two string inspired models: 1)
modifications to the Friedmann equations and 2) velocity dependent potentials.
The suppression of low ``l'' modes in the microwave background data arises due
to the new physics. In addition, the spectral index is red (n<1) on small
scales and blue (n>1) on large scales, in agreement with data.Comment: 18 pages, 2 figures, submitted for publication in Physical Review D,
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Genomic Profiling of Childhood Tumor Patient-Derived Xenograft Models to Enable Rational Clinical Trial Design.
Accelerating cures for children with cancer remains an immediate challenge as a result of extensive oncogenic heterogeneity between and within histologies, distinct molecular mechanisms evolving between diagnosis and relapsed disease, and limited therapeutic options. To systematically prioritize and rationally test novel agents in preclinical murine models, researchers within the Pediatric Preclinical Testing Consortium are continuously developing patient-derived xenografts (PDXs)-many of which are refractory to current standard-of-care treatments-from high-risk childhood cancers. Here, we genomically characterize 261 PDX models from 37 unique pediatric cancers; demonstrate faithful recapitulation of histologies and subtypes; and refine our understanding of relapsed disease. In addition, we use expression signatures to classify tumors for TP53 and NF1 pathway inactivation. We anticipate that these data will serve as a resource for pediatric oncology drug development and will guide rational clinical trial design for children with cancer
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