821 research outputs found
Ultraviolet Complete Quantum Gravity
An ultraviolet complete quantum gravity theory is formulated in which vertex
functions in Feynman graphs are entire functions and the propagating graviton
is described by a local, causal propagator. The cosmological constant problem
is investigated in the context of the ultraviolet complete quantum gravity.Comment: 11 pages, no figures. Changes to text. Results remain the same.
References added. To be published in European Physics Journal Plu
Gravitational anomalies in a dispersive approach
The gravitational anomalies in two dimensions, specifically the Einstein
anomaly and the Weyl anomaly, are fully determined by means of dispersion
relations. In this approach the anomalies originate from the peculiar infrared
feature of the imaginary part of the relevant formfactor which approaches a
-function singularity at zero momentum squared when .Comment: 10 page
Conformal Supergravity in Twistor-String Theory
Conformal supergravity arises in presently known formulations of
twistor-string theory either via closed strings or via gauge-singlet open
strings. We explore this sector of twistor-string theory, relating the relevant
string modes to the particles and fields of conformal supergravity. We also use
the twistor-string theory to compute some tree level scattering amplitudes with
supergravitons, and compare to expectations from conformal supergravity. Since
the supergravitons interact with the same coupling constant as the Yang-Mills
fields, conformal supergravity states will contribute to loop amplitudes of
Yang-Mills gluons in these theories. Those loop amplitudes will therefore not
coincide with the loop amplitudes of pure super Yang-Mills theory.Comment: 43 pages harvmac tex, added footnote to introductio
Effects of foal presence at milking and dietary extra virgin olive oil on jennet milk fatty acids profile
TwelveRagusanajennetswerestudiedtoinvestigatetheeffectsof dietaryextra Twelve Ragusana jennets were studiedtoinvestigatetheeffectsof dietaryextra studied to investigatetheeffectsof dietaryextra the effects of dietaryextra dietary extra virgin olive oil and thepresenceofthefoal duringmilkingonmilkfattyacids(FA)profile.At20, 50 thepresenceofthefoal duringmilkingonmilkfattyacids(FA)profile.At20, 50 he presence of the foal during milking on milk fatty acids (FA) profile. At 20, 50 and 90 days post-foaling, each jennet was milked 4 times per day. The feeding system and the milking procedures are given by Alabiso et al. (2009). FA profiles of the composites from milkings without foals (1MNF+3MNF) and with foals (2MYF+4MYF) were analyzed by gas chromatography. Dietary oil had no significant effect on milk yield or fat content but increased the proportion of C18:1 (n-9) in milk. Jen- net milk had a beneficial FA profile compared to bovine milk and thus would be suitable for consump- tion by infants suffering from cows milk protein allergy, however, augmentation of the long-chain n-3 polyunsaturated FA content warrants further study
The 3-graviton vertex function in thermal quantum gravity
The high temperature limit of the 3-graviton vertex function is studied in
thermal quantum gravity, to one loop order. The leading () contributions
arising from internal gravitons are calculated and shown to be twice the ones
associated with internal scalar particles, in correspondence with the two
helicity states of the graviton. The gauge invariance of this result follows in
consequence of the Ward and Weyl identities obeyed by the thermal loops, which
are verified explicitly.Comment: 19 pages, plain TeX, IFUSP/P-100
General structure of the graviton self-energy
The graviton self-energy at finite temperature depends on fourteen structure
functions. We show that, in the absence of tadpoles, the gauge invariance of
the effective action imposes three non-linear relations among these functions.
The consequences of such constraints, which must be satisfied by the thermal
graviton self-energy to all orders, are explicitly verified in general linear
gauges to one loop order.Comment: 4 pages, minor corrections of typo
Thermal one- and two-graviton Green's functions in the temporal gauge
The thermal one- and two-graviton Green's function are computed using a
temporal gauge. In order to handle the extra poles which are present in the
propagator, we employ an ambiguity-free technique in the imaginary-time
formalism. For temperatures T high compared with the external momentum, we
obtain the leading T^4 as well as the subleading T^2 and log(T) contributions
to the graviton self-energy. The gauge fixing independence of the leading T^4
terms as well as the Ward identity relating the self-energy with the one-point
function are explicitly verified. We also verify the 't Hooft identities for
the subleading T^2 terms and show that the logarithmic part has the same
structure as the residue of the ultraviolet pole of the zero temperature
graviton self-energy. We explicitly compute the extra terms generated by the
prescription poles and verify that they do not change the behavior of the
leading and sub-leading contributions from the hard thermal loop region. We
discuss the modification of the solutions of the dispersion relations in the
graviton plasma induced by the subleading T^2 contributions.Comment: 17 pages, 5 figures. Revised version to be published in Phys. Rev.
Trace Anomaly and Backreaction of the Dynamical Casimir Effect
The Casimir energy for massless scalar field which satisfies priodic boundary
conditions in two-dimensional domain wall background is calculated by making
use of general properties of renormalized stress-tensor. The line element of
domain wall is time dependent, the trace anomaly which is the nonvanishing
for a conformally invariant field after renormalization,
represent the back reaction of the dynamical Casimir effect.Comment: 8 pages, no figures, typos corrected, discussion added, has been
accepted for the publication in GR
A pan-tissue DNA methylation atlas enables in silico decomposition of human tissue methylomes at cell-type resolution
Bulk-tissue DNA methylomes represent an average over many different cell types, hampering our understanding of cell-type-specific contributions to disease development. As single-cell methylomics is not scalable to large cohorts of individuals, cost-effective computational solutions are needed, yet current methods are limited to tissues such as blood. Here we leverage the high-resolution nature of tissue-specific single-cell RNA-sequencing datasets to construct a DNA methylation atlas defined for 13 solid tissue types and 40 cell types. We comprehensively validate this atlas in independent bulk and single-nucleus DNA methylation datasets. We demonstrate that it correctly predicts the cell of origin of diverse cancer types and discovers new prognostic associations in olfactory neuroblastoma and stage 2 melanoma. In brain, the atlas predicts a neuronal origin for schizophrenia, with neuron-specific differential DNA methylation enriched for corresponding genome-wide association study risk loci. In summary, the DNA methylation atlas enables the decomposition of 13 different human tissue types at a high cellular resolution, paving the way for an improved interpretation of epigenetic data
Photons and Gravitons as Goldstone Bosons, and the Cosmological Constant
We reexamine a scenario in which photons and gravitons arise as Goldstone
bosons associated with the spontaneous breaking of Lorentz invariance. We study
the emergence of Lorentz invariant low energy physics in an effective field
theory framework, with non-Lorentz invariant effects arising from radiative
corrections and higher order interactions. Spontaneous breaking of the Lorentz
group also leads to additional exotic but weakly coupled Goldstone bosons,
whose dispersion relations we compute. The usual cosmological constant problem
is absent in this context: being a Goldstone boson, the graviton can never
develop a potential, and the existence of a flat spacetime solution to the
field equations is guaranteed.Comment: 21 pages, harvma
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