2,590 research outputs found
Extracting New Physics from the CMB
We review how initial state effects generically yield an oscillatory
component in the primordial power spectrum of inflationary density
perturbations. These oscillatory corrections parametrize unknown new physics at
a scale and are potentially observable if the ratio is
sufficiently large. We clarify to what extent present and future CMB data
analysis can distinguish between the different proposals for initial state
corrections.Comment: Invited talk by B. Greene at the XXII Texas Symposium on Relativistic
Astrophysics, Stanford University, 13-17 December 2004, (TSRA04-0001), 8
pages, LaTeX, some references added, added paragraph at the end of section 2
and an extra note added after the conclusions regarding modifications to the
large k power spectra deduced from galaxy survey
Studies of new media radiation induced laser
Various lasants were investigated especially, 2-iodohepafluoropropane (i-C3F7I) for the direct solar pumped lasers. Optical pumping of iodine laser was achieved using a small flashlamp. Using i-C3F7I as a laser gain medium, threshold inversion density, small signal gain, and laser performance at the elevated temperature were measured. The experimental results and analysis are presented. The iodine laser kinetics of the C3F7I and IBr system were numerically simulated. The concept of a direct solar-pumped laser amplifier using (i-C3F7I) as the laser material was evaluated and several kinetic coefficients for i-C3F7I laser system were reexamined. The results are discussed
No CPT Violation from Tilted Brane in Neutral Meson--Antimeson Systems
Tilted brane in theories with large compact extra dimensions leads to
spontaneous symmetry breaking of the Lorentz and rotational invariance in four
dimensions, as shown by Dvali and Shifman. In this brief report, we point out
that the mentioned Lorentz symmetry breaking, although leading to the
CPT--violating interaction terms, cannot lead to the CPT violation in the
experimentally interesting -- and analogous systems.Comment: 5 pages, RevTe
Boundary Effective Field Theory and Trans-Planckian Perturbations: Astrophysical Implications
We contrast two approaches to calculating trans-Planckian corrections to the
inflationary perturbation spectrum: the New Physics Hypersurface [NPH] model,
in which modes are normalized when their physical wavelength first exceeds a
critical value, and the Boundary Effective Field Theory [BEFT] approach, where
the initial conditions for all modes are set at the same time, and modified by
higher dimensional operators enumerated via an effective field theory
calculation. We show that these two approaches -- as currently implemented --
lead to radically different expectations for the trans-Planckian corrections to
the CMB and emphasize that in the BEFT formalism we expect the perturbation
spectrum to be dominated by quantum gravity corrections for all scales shorter
than some critical value. Conversely, in the NPH case the quantum effects only
dominate the longest modes that are typically much larger than the present
horizon size. Furthermore, the onset of the breakdown in the standard
inflationary perturbation calculation predicted by the BEFT formalism is likely
to be associated with a feature in the perturbation spectrum, and we discuss
the observational signatures of this feature in both CMB and large scale
structure observations. Finally, we discuss possible modifications to both
calculational frameworks that would resolve the contradictions identified here.Comment: Reworded commentary, reference added (v2) References added (v3
Multimodal Treatment in Metastatic Colorectal Cancer (mCRC) Improves Outcomes—The University College London Hospital (UCLH) Experience
Background: Despite notable advances in the management of metastatic colorectal cancer (mCRC) over the last two decades, treatment intent in the vast majority of patients remains palliative due to technically unresectable disease, extensive disease, or co-morbidities precluding major surgery. Up to 30% of individuals with mCRC are considered potentially suitable for primary or metastasis-directed multimodal therapy, including surgical resection, ablative techniques, or stereotactic radiotherapy (RT), with the aim of improving survival outcomes. We reviewed the potential benefits of multimodal therapy on the survival of patients with mCRC treated at the UCLH. Methods: Clinical data on baseline characteristics, multimodal treatments, and survival outcomes were retrospectively collected from all patients with mCRC receiving systemic chemotherapy between January 2013 and April 2017. Primary outcome was the impact of multimodal therapy on overall survival, compared to systemic therapy alone, and the effect of different types of multimodal therapy on survival outcome, and was assessed using the Kaplan–Meier approach. All analyses were adjusted for age, gender, and side of primary tumour. Results: One-hundred and twenty-five patients with mCRC were treated during the study period (median age: 62 years (range 19–89). The liver was the most frequent metastatic site (78%; 97/125). A total of 52% (65/125) had ≥2 lines of systemic chemotherapy. Of the 125 patients having systemic chemotherapy, 74 (59%) underwent multimodal treatment to the primary tumour or metastasis. Median overall survival (OS) was 25.7 months [95% Confidence Interval (CI) 21.5–29.0], and 3-year survival, 26%. Univariate analysis demonstrated that patients who had additional procedures (surgery/ablation/RT) were significantly less likely to die (Hazard Ratio (HR) 0.18, 95% CI 0.12–0.29, p < 0.0001) compared to those receiving systemic chemotherapy alone. Increasing number of multimodal procedures was associated with an incremental increase in survival—with median OS 28.4 m, 35.7 m, and 64.8 m, respectively, for 1, 2, or ≥3 procedures (log-rank p < 0.0001). After exclusion of those who received systemic chemotherapy only (n = 51), metastatic resections were associated with improved survival (adjusted HR 0.36, 95% CI 0.20–0.63, p < 0.0001), confirmed in multivariate analysis. Multiple single-organ procedures did not improve survival. Conclusion: Multimodal therapy for metastatic bowel cancer is associated with significant survival benefit. Resection/radical RT of the primary and resection of metastatic disease should be considered to improve survival outcomes following multidisciplinary team (MDT) discussion and individual assessment of fitness
Direct Signals for Large Extra Dimensions in the Production of Fermion Pairs at Linear Colliders
We analyze the potentiality of the new generation of linear
colliders to search for large extra dimensions via the production of fermion
pairs in association with Kaluza-Klein gravitons (G), i.e. . This process leads to a final state exhibiting a significant amount
of missing energy in addition to acoplanar lepton or jet pairs. We study in
detail this reaction using full tree level contibutions due to the graviton
emission and the standard model backgrounds. After choosing the cuts to enhance
the signal, we show that a linear collider with a center-of-mass energy of 500
GeV will be able to probe quantum gravity scales from 0.96(0.86) up to 4.1(3.3)
TeV at 2(5) level, depending on the number of extra dimensions.Comment: 19 pages, 5 figures. Using RevTex, axodraw.sty. Discussion was
extended. No changes in the results. Accepted for publication by Phys. Rev.
Finite Temperature Systems of Brane-Antibrane on a Torus
In order to study the thermodynamic properties of brane-antibrane systems in
the toroidal background, we compute the finite temperature effective potential
of tachyon T in this system on the basis of boundary string field theory. We
first consider the case that all the radii of the target space torus are about
the string scale. If the Dp-antiDp pair is extended in all the non-compact
directions, the sign of the coefficient of |T|^2 term of the potential changes
slightly below the Hagedorn temperature. This means that a phase transition
occurs near the Hagedorn temperature. On the other hand, if the Dp-antiDp pair
is not extended in all the non-compact directions, the coefficient is kept
negative, and thus a phase transition does not occur. Secondly, we consider the
case that some of the radii of the target space torus are much larger than the
string scale and investigate the behavior of the potential for each value of
the radii and the total energy. If the Dp-antiDp pair is extended in all the
non-compact directions, a phase transition occurs for large enough total
energy.Comment: 23 pages, 3 figures, minor errors corrected, version to appear in
JHE
Warped Reheating in Multi-Throat Brane Inflation
We investigate in some quantitative details the viability of reheating in
multi-throat brane inflationary scenarios by estimating and comparing the time
scales for the various processes involved. We also calculate within
perturbative string theory the decay rate of excited closed strings into KK
modes and compare with that of their decay into gravitons; we find that in the
inflationary throat the former is preferred. We also find that over a small but
reasonable range of parameters of the background geometry, these KK modes will
preferably tunnel to another throat (possibly containing the Standard Model)
instead of decaying to gravitons due largely to their suppressed coupling to
the bulk gravitons. Once tunneled, the same suppressed coupling to the
gravitons again allows them to reheat the Standard Model efficiently. We also
consider the effects of adding more throats to the system and find that for
extra throats with small warping, reheating still seems viable.Comment: 29 pages, 4 figures, discussions on closed string decay expanded,
references adde
Fractional branes, warped compactifications and backreacted orientifold planes
The standard extremal p-brane solutions in supergravity are known to allow
for a generalisation which consists of adding a linear dependence on the
world-volume coordinates to the usual harmonic function. In this note we
demonstrate that remarkably this generalisation goes through in exactly the
same way for p-branes with fluxes added to it that correspond to fractional
p-branes. We relate this to warped orientifold compactifications by trading the
Dp-branes for Op-planes that solve the RR tadpole condition. This allows us to
interpret the worldvolume dependence as due to lower-dimensional scalars that
flow along the massless directions in the no-scale potential. Depending on the
details of the fluxes these flows can be supersymmetric domain wall flows. Our
solutions provide explicit examples of backreacted orientifold planes in
compactifications with non-constant moduli.Comment: 20 pages, incl. references. v2: small changes required for JHEP
publication. v3: few equation typos correcte
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