A symmetry for vanishing cosmological constant

Two different realizations of a symmetry principle that impose a zero cosmological constant in an extra-dimensional set-up are studied. The symmetry is identified by multiplication of the metric by minus one. In the first realization of the symmetry this is provided by a symmetry transformation that multiplies the coordinates by the imaginary number i. In the second realization this is accomplished by a symmetry transformation that multiplies the metric tensor by minus one. In both realizations of the symmetry the requirement of the invariance of the gravitational action under the symmetry selects out the dimensions given by D = 2(2n+1), n=0,1,2,... and forbids a bulk cosmological constant. Another attractive aspect of the symmetry is that it seems to be more promising for quantization when compared to the usual scale symmetry. The second realization of the symmetry is more attractive in that it is posible to make a possible brane cosmological constant zero in a simple way by using the same symmetry, and the symmetry may be identified by reflection symmetry in extra dimensions.Comment: Talk in the conference IRGAC 2006, 2nd International Conference on Quantum Theories and Renormalization Group in Gravity and Cosmology, Barcelon

Vacuum properties of nonsymmetric gravity in de Sitter space

We consider quantum effects of a massive antisymmetric tensor field on the dynamics of de Sitter space-time. Our starting point is the most general, stable, linearized Lagrangian arising in nonsymmetric gravitational theories (NGTs), where part of the antisymmetric field mass is generated by the cosmological term. We construct a renormalization group (RG) improved effective action by integrating out one loop vacuum fluctuations of the antisymmetric tensor field and show that, in the limit when the RG scale goes to zero, the Hubble parameter -- and thus the effective cosmological constant -- relaxes rapidly to zero. We thus conclude that quantum loop effects in de Sitter space can dramatically change the infrared sector of the on-shell gravity, making the expansion rate insensitive to the original (bare) cosmological constant.Comment: 32 pages, 2 eps figure

Late transient acceleration of the universe in string theory on S1/Z2S^{1}/Z_{2}

Recently, in Gong {\em et al} \cite{GWW07} and Wang and Santos \cite{WS07} it was shown that the effective cosmological constant on each of the two orbifold branes can be easily lowered to its current observational value, by using the large extra dimensions in the framework of both M-Theory and string theory on $S^{1}/Z_{2}$. In this paper, we study the current acceleration of the universe, using the formulas developed in \cite{WS07}. We first construct explicitly time-dependent solution to the 10-dimensional bulk of the Neveu-Schwarz/Neveu-Schwarz sector, compactified on a 5-dimensional torus. Then, we write down the generalized Friedmann equations on each of the two dynamical branes, and fit the models to the 182 gold supernova Ia data and the BAO parameter from SDSS, using both of our MINUIT and Monte-Carlo Markov Chain (MCMC) codes. With the best fitting values of the parameters involved as initial conditions, we integrate the generalized Friedmann equations numerically and find the future evolution of the universe. We find that it depends on the choice of the radion potentials $V_{4}^{(I)} (I = 1, 2)$ of the branes. In particular, when choosing them to be the Goldberger-Wise potentials, $V_{4}^{(I)} = \lambda_{4}^{(I)} (\psi^{2} - {v_{I}}^{2})^{2}$, we find that the current acceleration of the universe driven by the effective cosmological constant is only temporary. Due to the effects of the potentials, the universe will be finally in its decelerating expansion phase again. We also study the proper distance between the two branes, and find that it remains almost constant during the whole future evolution of the universe in all the models considered.Comment: revtex4, 18 figures. Typos corrected and new References added. Version to be published in JCA

From Big Bang to Asymptotic de Sitter: Complete Cosmologies in a Quantum Gravity Framework

Using the Einstein-Hilbert approximation of asymptotically safe quantum gravity we present a consistent renormalization group based framework for the inclusion of quantum gravitational effects into the cosmological field equations. Relating the renormalization group scale to cosmological time via a dynamical cutoff identification this framework applies to all stages of the cosmological evolution. The very early universe is found to contain a period of ``oscillatory inflation'' with an infinite sequence of time intervals during which the expansion alternates between acceleration and deceleration. For asymptotically late times we identify a mechanism which prevents the universe from leaving the domain of validity of the Einstein-Hilbert approximation and obtain a classical de Sitter era.Comment: 47 pages, 17 figure

High-risk human papillomavirus clearance in pregnant women: trends for lower clearance during pregnancy with a catch-up postpartum

We followed 353 women referred with abnormal cervical cytology in a non-intervention cohort study. In 91 pregnant women we compared high-risk human papilloma virus rates in the subsequent trimesters and postpartum in comparison to 262 non-pregnant women. High-risk human papilloma virus clearance was compared with 179 high-risk human papilloma virus positive non-pregnant women. Our main questions were: (1) do high-risk human papilloma virus rates change during pregnancy?; and (2) is there any difference between high-risk human papilloma virus clearance in pregnant and non-pregnant women? Women were monitored 3–4 monthly by cytology, colposcopy, and high-risk human papilloma virus testing. The median follow-up time was 33 months (range 3–74). Non-pregnant women showed prevalence rates of high-risk human papilloma virus of 64, 57, 53, and 50%, respectively, in four subsequent 3-months periods since the start of the study. These high-risk human papilloma virus rates were higher than in the three trimesters of pregnancy, and during the first 3 months postpartum, i.e. 50, 44, 45, and 31%, respectively. Postpartum only, this difference was statistically significant (P=0.004). Paired comparisons of high-risk human papilloma virus prevalence rates of the different trimesters with the postpartum rate showed (McNemar test) decreased rates: first trimester: 18% (P=0.02), second trimester: 13% (P=0.02) and third trimester: 23% (P<0.005). Such a phenomenon was not found in non-pregnant women. Pregnant women showed a trend for increased high-risk human papilloma virus clearance during the third trimester and postpartum compared to non-pregnant women (hazard ratios 3.3 (0.8–13.7) and 4.6 (1.6–12.8), respectively). These results suggest a lowered immune-response against human papilloma virus during the first two trimesters of pregnancy with a catch-up postpartum

Beyond Teenage and Young Adult Cancer Care: Care Experiences of Patients Aged 25-39 Years Old in the UK National Health Service.

AimsAdolescents and young adults aged 15-39 years with cancer face unique medical, practical and psychosocial issues. In the UK, principal treatment centres and programmes have been designed to care for teenage and young adult patients aged 13-24 years in an age-appropriate manner. However, for young adults (YAs) aged 25-39 years with cancer, little access to age-specific support is available. The aim of this study was to examine this possible gap by qualitatively exploring YA care experiences, involving patients as research partners in the analysis to ensure robust results.Materials and methodsWe conducted a phenomenological qualitative study with YAs diagnosed with any cancer type between ages 25 and 39 years old in the last 5 years. Participants took part in interviews or focus groups and data were analysed using inductive thematic analysis. Results were shaped in an iterative process with the initial coders and four YA patients who did not participate in the study to improve the rigor of the results.ResultsSixty-five YAs with a range of tumour types participated. We identified seven themes and 13 subthemes. YAs found navigating the healthcare system difficult and commonly experienced prolonged diagnostic pathways. Participants felt under-informed about clinical details and the long-term implications of side-effects on daily life. YAs found online resources overwhelming but also a source of information and treatment support. Some patients regretted not discussing fertility before cancer treatment or felt uninformed or rushed when making fertility preservation decisions. A lack of age-tailored content or age-specific groups deterred YAs from accessing psychological support and rehabilitation services.ConclusionsYAs with cancer may miss some benefits provided to teenagers and young adults in age-tailored cancer services. Improving services for YAs in adult settings should focus on provision of age-specific information and access to existing relevant support

MRI measurement of residual cervical length after radical trachelectomy for cervical cancer and the risk of adverse pregnancy outcomes: a blinded imaging analysis.

Objective To determine the association between the residual cervix measured on postoperative MRI after radical vaginal trachelectomy (RVT) and adverse obstetrical outcomes.Design Observational study.Setting Referral Cancer centre.Population Women who conceived after RVT for cervical cancer at the Royal Marsden Hospital, London, between 1995 and 2015.Methods Postoperative MRI scans were analysed by three researchers. The agreement between researchers was assessed by Pearson's correlation coefficient and Bland-Altman plot. Patients were divided into two groups (<10 and ≥10 mm residual cervix) for the analysis of adverse obstetrical outcomes.Main outcome measures Late miscarriage, premature delivery, premature rupture of membranes (PROM) and chorioamnionitis.Results Thirty-one MRI scans were available; 29 of these women had a pregnancy that progressed beyond the first trimester. There was a strong reproducibility of the measurement of residual cervix (P < 0.001). Nineteen women (65.5%) had <10 mm residual cervix and 10 (34.5%) had ≥10 mm. Among women with <10 mm residual cervix, seven (36.8%) experienced PROM and ten (66.7%) had a preterm birth; No women with ≥10 mm residual cervix had PROM and two (22.2%) had a preterm birth (P = 0.028 and P = 0.035, respectively). Overall, there were nine (16.7%) first-trimester miscarriages, six (11.1%) late fetal losses, 12 (31.6%) preterm births and 36 (66.7%) live births. After a mean follow up of 78.1 months, 36 women were disease-free and one woman had died.Conclusions MRI measurements of the residual cervix are reproducible between observers. The incidence of PROM and premature delivery is higher when the residual cervix after RVT is <10 mm.Tweetable abstract The risk of prematurity after RVT can be predicted from measurements of residual cervical length on postoperative MRI scan

Is the evidence for dark energy secure?

Several kinds of astronomical observations, interpreted in the framework of the standard Friedmann-Robertson-Walker cosmology, have indicated that our universe is dominated by a Cosmological Constant. The dimming of distant Type Ia supernovae suggests that the expansion rate is accelerating, as if driven by vacuum energy, and this has been indirectly substantiated through studies of angular anisotropies in the cosmic microwave background (CMB) and of spatial correlations in the large-scale structure (LSS) of galaxies. However there is no compelling direct evidence yet for (the dynamical effects of) dark energy. The precision CMB data can be equally well fitted without dark energy if the spectrum of primordial density fluctuations is not quite scale-free and if the Hubble constant is lower globally than its locally measured value. The LSS data can also be satisfactorily fitted if there is a small component of hot dark matter, as would be provided by neutrinos of mass 0.5 eV. Although such an Einstein-de Sitter model cannot explain the SNe Ia Hubble diagram or the position of the `baryon acoustic oscillation' peak in the autocorrelation function of galaxies, it may be possible to do so e.g. in an inhomogeneous Lemaitre-Tolman-Bondi cosmology where we are located in a void which is expanding faster than the average. Such alternatives may seem contrived but this must be weighed against our lack of any fundamental understanding of the inferred tiny energy scale of the dark energy. It may well be an artifact of an oversimplified cosmological model, rather than having physical reality.Comment: 12 pages, 5 figures; to appear in a special issue of General Relativity and Gravitation, eds. G.F.R. Ellis et al; Changes: references reformatted in journal style - text unchange

Filtering out the cosmological constant in the Palatini formalism of modified gravity

According to theoretical physics the cosmological constant (CC) is expected to be much larger in magnitude than other energy densities in the universe, which is in stark contrast to the observed Big Bang evolution. We address this old CC problem not by introducing an extremely fine-tuned counterterm, but in the context of modified gravity in the Palatini formalism. In our model the large CC term is filtered out, and it does not prevent a standard cosmological evolution. We discuss the filter effect in the epochs of radiation and matter domination as well as in the asymptotic de Sitter future. The final expansion rate can be much lower than inferred from the large CC without using a fine-tuned counterterm. Finally, we show that the CC filter works also in the Kottler (Schwarzschild-de Sitter) metric describing a black hole environment with a CC compatible to the future de Sitter cosmos.Comment: 22 pages, 1 figure, discussion extended, references added, accepted by Gen.Rel.Gra

MSLED, Neutrino Oscillations and the Cosmological Constant

We explore the implications for neutrino masses and mixings within the minimal version of the supersymmetric large-extra-dimensions scenario (MSLED). This model was proposed in {\tt hep-ph/0404135} to extract the phenomenological implications of the promising recent attempt (in {\tt hep-th/0304256}) to address the cosmological constant problem. Remarkably, we find that the simplest couplings between brane and bulk fermions within this approach can lead to a phenomenologically-viable pattern of neutrino masses and mixings that is also consistent with the supernova bounds which are usually the bane of extra-dimensional neutrino models. Under certain circumstances the MSLED scenario can lead to a lepton mixing (PMNS) matrix close to the so-called bi-maximal or the tri-bimaximal forms (which are known to provide a good description of the neutrino oscillation data). We discuss the implications of MSLED models for neutrino phenomenology.Comment: 38 pages, 1 figure; Reposted with a few additional reference