1,085 research outputs found
Hybrid quantization of an inflationary universe
We quantize to completion an inflationary universe with small inhomogeneities
in the framework of loop quantum cosmology. The homogeneous setting consists of
a massive scalar field propagating in a closed, homogeneous scenario. We
provide a complete quantum description of the system employing loop
quantization techniques. After introducing small inhomogeneities as scalar
perturbations, we identify the true physical degrees of freedom by means of a
partial gauge fixing, removing all the local degrees of freedom except the
matter perturbations. We finally combine a Fock description for the
inhomogeneities with the polymeric quantization of the homogeneous background,
providing the quantum Hamiltonian constraint of the composed system. Its
solutions are then completely characterized, owing to the suitable choice of
quantum constraint, and the physical Hilbert space is constructed. Finally, we
consider the analog description for an alternate gauge and, moreover, in terms
of gauge-invariant quantities. In the deparametrized model, all these
descriptions are unitarily equivalent at the quantum level.Comment: 16 pages, no figure
Racetrack Potentials and the de Sitter Swampland Conjectures
We show that one can find de Sitter critical points (saddle points) in models
of flux compactification of Type IIB String Theory without any uplifting terms
and in the presence of several moduli. We demonstrate this by giving explicit
examples following some of the ideas recently presented by Conlon in [1], as
well as more generic situations where one can violate the strong form of the de
Sitter Swampland Conjecture. We stabilize the complex structure and the dilaton
with fluxes, and we introduce a racetrack potential that fixes the K\"ahler
moduli. The resultant potentials generically exhibit de Sitter critical points
and satisfy several consistency requirements such as flux quantization, large
internal volume, and weak coupling, as well as a form of the so-called Weak
Gravity Conjecture. Furthermore, we compute the form of the potential around
these de Sitter saddle points and comment on these results in connection to the
refined and more recent version of the de Sitter Swampland Conjecture.Comment: 23 pages, 4 figures; updated to reflect version accepted to JHE
Reduction of Murine Cutaneous UVB-Induced Tumor-Infiltrating T Lymphocytes by Dietary Canthaxanthin
The effect of dietary canthaxanthin, retinyl palmitate, or their combination on the tumor-infiltrating T-lymphocyte response (T-TIL) in de novo murine ultraviolet type B irradiation-induced tumors was investigated to elucidate potential mechanisms of action of these compounds. We found that dietary canthaxanthin greatly reduced the number of tumor-infiltrating helper/inducer, suppressor/cytotoxic, and interleukin-2 receptor-positive T lymphocytes and also observed a concomitant statistically significant increase in tumour incidence in canthaxanthin-fed animals. The addition of retinyl palmitate to the canthaxanthin diet ameliorated this negative effect on TIL and the development of skin tumors. We conclude that dietary retinyl palmitate and canthaxanthin can modulate the host T-cell immune response within a growing tumor and may affect tumorigenicity
Methotrexate in Pediatric Osteosarcoma: Response and Toxicity in Relation to Genetic Polymorphisms and Dihydrofolate Reductase and Reduced Folate Carrier 1 Expression
To determine the influence of the genotype and the level of expression of different enzymes involved in folate metabolism on the response to and toxicity of high-dose methotrexate treatment in pediatric osteosarcomas.
STUDY DESIGN: DHFR and Reduced folate carrier 1 (RFC1) semiquantitative expression was analyzed in 34 primary and metastatic osteosarcoma tissues by real-time polymerase chain reaction. The following polymorphisms were also analyzed in peripheral blood from 96 children with osteosarcoma and 110 control subjects: C677T, A1298C (MTHFR), G80A (RFC1), A2756G (MTR), C1420T (SHMT), the 28bp-repeat polymorphism, and 1494del6 of the TYMS gene. Treatment toxicity was scored after each cycle according to criteria from the World Health Organization.
RESULTS: DHFR and RFC1 expression was lower in initial osteosarcoma biopsy specimens than in metastases (P = .024 and P = .041, respectively). RFC1 expression was moderately decreased in samples with poor histologic response to preoperative treatment (P = .053). Patients with osteosarcoma with G3/G4 hematologic toxicity were more frequently TT than CT/CC for C677T/MTHFR (P = .023) and GG for A2756G/MTR (P = .048 and P = .057 for gastrointestinal and hematologic toxicity, respectively).
CONCLUSIONS: The role of C677T/MTHFR and A2756G/MTR on chemotherapy-induced toxicity should be further investigated in pediatric osteosarcomas receiving high-dose methotrexate. Altered expression of DHFR and RFC1 is a feasible mechanism by which osteosarcoma cells become resistant to methotrexate
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