Estonian National Institute of Chemical Physics and Biophysics

Tallinn, Estonia

Estonian National Institute of Chemical Physics and Biophysics

Tallinn, Estonia
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Vaskonen V.,Estonian National Institute of Chemical Physics and Biophysics
Physical Review D | Year: 2017

We consider a real scalar singlet field which provides a strong first-order electroweak phase transition via its coupling to the Higgs boson, and gives a CP violating contribution on the top quark mass via a dimension-6 operator. We study the correlation between the baryon-to-entropy ratio produced by electroweak baryogenesis, and the gravitational wave signal from the electroweak phase transition. We show that future gravitational wave experiments can test, in particular, the region of the model parameter space where the observed baryon-to-entropy ratio can be obtained even if the new physics scale, which is explicit in the dimension-6 operator, is high. © 2017 American Physical Society.

Giudice G.F.,CERN | Strumia A.,Estonian National Institute of Chemical Physics and Biophysics
Nuclear Physics B | Year: 2012

We study the range of Higgs masses predicted by High-Scale Supersymmetry and by Split Supersymmetry, using the matching condition for the Higgs quartic coupling determined by the minimal field content. In the case of Split Supersymmetry, we compute for the first time the complete next-to-leading order corrections, including two-loop renormalization group equations and one loop threshold effects. These corrections reduce the predicted Higgs mass by a few GeV. We investigate the impact of the recent LHC Higgs searches on the scale of supersymmetry breaking. In particular, we show that an upper bound of 127 GeV on the Higgs mass implies an upper bound on the scale of Split Supersymmetry of about 10 8 GeV, while no firm conclusion can yet be drawn for High-Scale Supersymmetry. © 2012 Elsevier B.V.

Kahru A.,Estonian National Institute of Chemical Physics and Biophysics | Ivask A.,Estonian National Institute of Chemical Physics and Biophysics | Ivask A.,University of California at Los Angeles
Accounts of Chemical Research | Year: 2013

Some researchers consider nanotechnology the next industrial revolution, and consumer products and a variety of industries increasingly use synthetic nanoparticles. In this Account, we review the initial accomplishments of nanoecotoxicology, a discipline that is just a decade old. This new subdiscipline of ecotoxicology faces two important and challenging problems: the analysis of the safety of nanotechnologies in the natural environment and the promotion of sustainable development while mitigating the potential pitfalls of innovative nanotechnologies. In this Account, we provide a snapshot of the publicly available scientific information regarding the ecotoxicity of engineered nanoparticles. We pay special attention to information relevant to aquatic freshwater species commonly used for risk assessment and regulation.Just as the development of ecotoxicology has lagged behind that of toxicology, nanoecotoxicological research has developed much more slowly than nanotoxicology. Although the first nanotoxicolology papers were published in 1990s, the first nanoecotoxicology papers came out in 2006. A meta-analysis of scientific publications covering different environmental impacts of nanomaterials showed that the importance of research into the environmental impact of nanotechnology has gradually increased since 2005. Now the most frequently cited papers in the environmental disciplines are often those that focus on synthetic nanoparticles.The first nanoecotoxicology studies focused on adverse effects of nanoparticles on fish, algae and daphnids, which are ecotoxicological model organisms for classification and labeling of chemicals (these model organisms are also used in the EU chemical safety policy adopted in 2007: Registration, Evaluation, Authorization, and Restriction of Chemicals (REACH)). Based on our experience, we propose a multitrophic battery of nanoecotoxicological testing that includes particle-feeding and a priori particle-"proof" prokaryotic and eukaryotic organisms at different food-chain levels. Using this battery of selected test organisms, we demonstrated that TiO2 nanoparticles were toxic to algae and that ZnO and CuO nanoparticles were toxic to several aquatic invertebrate test species. Thus, one single biotest cannot predict the ecotoxicological effects of chemicals/nanoparticles, and researchers should use several tests instead. Moreover, produced nanoparticles usually vary in features such as size, shape, and coating; therefore, a single nanoparticle species may actually include many entities with different physicochemical properties. An ecotoxicity analysis of all these variants would require a huge number of laboratory tests. To address these issues, high throughput bioassays and computational (QSAR) models that serve as powerful alternatives to conventional (eco)toxicity testing must be implemented to handle both the diversity of nanomaterials and the complexity of ecosystems. © 2012 American Chemical Society.

Fowlie A.,Estonian National Institute of Chemical Physics and Biophysics | Marzola L.,University of Tartu
Nuclear Physics B | Year: 2014

Motivated by a hint in a CMS search for right-handed W-bosons in eejj final states, we propose an experimental test of quark-mixing matrices in a general left-right symmetric model, based on counting the numbers of b-tags from right-handed W-boson hadronic decays. We find that, with our test, differences between left- and right-handed quark-mixing matrices could be detected at the LHC with s=14 TeV. With an integrated luminosity of about 20/fb, our test is sensitive to right-handed quark-mixing angles as small as about 30° and with 3000/fb, our test's sensitivity improves to right-handed mixing angles as small as about 7.5°. Our test's sensitivity might be further enhanced by tuning b-tagging efficiency against purity. © 2014 The Authors.

Hektor A.,Estonian National Institute of Chemical Physics and Biophysics | Marzola L.,University of Tartu
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

Coy dark matter removes the tension between the traditional WIMP paradigm of dark matter and the latest exclusion bounds from direct detection experiments. In this paper we present a leptophilic coy dark matter model that, on top of explaining the spatially extended 1-5 GeV γ-ray excess detected at the galactic center, reconciles the measured anomalous magnetic moment of muon with the corresponding standard model prediction. The annihilation channel of dark matter is χχ→ττ¯ with the dark matter mass mχ=9.43(-0.52+.063stat)(±1.2sys)GeV given by best-fit of the γ-ray excess. Fitting the measured anomalous magnetic moment of the muon requires instead a pseudoscalar mediator with a minimal mass ma=12-3+7GeV. © 2014 American Physical Society.

Kahru A.,Estonian National Institute of Chemical Physics and Biophysics | Dubourguier H.-C.,Estonian National Institute of Chemical Physics and Biophysics
Toxicology | Year: 2010

For hazard assessment of NPs quantitative nanoecotoxicological data are required. The objective of this review was to evaluate the currently existing literature data on toxicity (L(E)C50 values) of synthetic NPs in environmentally relevant species in order to: (i) identify tentatively most harmful NPs and most sensitive organism groups, and (ii) to provide relevant ecotoxicological information for further risk assessment. The focus was set on selected synthetic NPs (nano TiO2, nano ZnO, nano CuO, nano Ag, SWCNTs, MWCNs and C60-fullerenes) and organism groups representing main food-chain levels (bacteria, algae, crustaceans, ciliates, fish, yeasts and nematodes).Altogether 77 effect values were found, mostly for nano TiO2 (31%), C60 (18%), nano ZnO (17%), nano Ag (13%), SWCNTs and nano CuO (both 9%). Only 3% of the available quantitative ecotoxicological information concerned MWCNTs. Organism-wise, 33% of the data concerned crustaceans, 27% bacteria, 14% algae and 13% fish. For all organism groups studied, solubility of CuO- and ZnO-NPs was a key factor in their aquatic toxicity.On the basis of the 34 median L(E)C50 values derived from 77 individual values, NPs were ranked according to their lowest median L(E)C50 value for the above described organism groups: the most harmful were nano Ag and nano ZnO that were classified " extremely toxic" , (L(E)C50<0.1mg/l), followed by C60 fullerenes and nano CuO that were classified " very toxic" , (L(E)C50 0.1-1mg/l). SWCNTs and MWCNTs were classified " toxic" (L(E)C50 1-10mg/l). Nano TiO2 was classified as " harmful" , (L(E)C50 10-100mg/l). Throughout, algae and crustaceans (daphnids) were most sensitive and thus probably most vulnerable organism groups in aquatic exposure to NPs. Very low L(E)C50 values should deserve thorough attention of environmental risk assessors for evaluation of the potential adverse effects of synthetic NPs on ecosystems. As the quantitative nanoecotoxicological data are still rare, further studies are needed. © 2009 Elsevier Ireland Ltd.

Kannike K.,Normal School of Pisa | Kannike K.,Estonian National Institute of Chemical Physics and Biophysics
European Physical Journal C | Year: 2012

A scalar potential of the form λ ab φ a 2φ a 2 is bounded from below if its matrix of quartic couplings λ ab is copositive-positive on non-negative vectors. Scalar potentials of this form occur naturally for scalar dark matter stabilised by a ℤ 2 symmetry. Copositivity criteria allow us to derive analytic necessary and sufficient vacuum stability conditions for the matrix λ ab. We review the basic properties of copositive matrices and analytic criteria for copositivity. To illustrate these, we re-derive the vacuum stability conditions for the inert doublet model in a simple way, and derive the vacuum stability conditions for the ℤ 2 complex singlet dark matter, and for the model with both a complex singlet and an inert doublet invariant under a global U(1) symmetry. © 2012 Springer-Verlag / Società Italiana di Fisica.

Tsirlin A.A.,Estonian National Institute of Chemical Physics and Biophysics
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

We report on the microscopic magnetic model of a spin-12 magnet BaV3O8. In contrast to earlier phenomenological analysis, our density-functional band-structure calculations combined with quantum Monte Carlo simulations establish a relatively simple and nonfrustrated model of weakly coupled spin chains with intrachain coupling J38 K and Néel temperature TN6 K, both in excellent agreement with experiment. The intrachain coupling between spin-12 V+4 ions takes place via two contiguous V+5O4 tetrahedra forming an extended superexchange pathway with the V+4-V+4 distance of 7.44 Å. Surprisingly, this pathway is preferred over shorter V+4-V+4 connections, owing to peculiarities in the interacting orbitals of the magnetic V+4 ions and V+5 ions that are nonmagnetic, but feature low-lying 3d states contributing to the superexchange process. We also note that the crystal structure of BaV3O8 supports the long-sought uniform arrangement of Dzyaloshinsky-Moriya (DM) couplings on a spin-12 chain. While our calculations yield only a weak DM anisotropy in BaV3O8, the crystal structure of this compound provides a suitable framework for the search of spin chains with the uniform DM anisotropy in other compounds of the vanadate family. © 2014 American Physical Society.

Fowlie A.,Estonian National Institute of Chemical Physics and Biophysics
European Physical Journal C | Year: 2014

With Bayesian statistics, we investigate the full parameter space of the constrained “next-to-minimal” supersymmetric standard model (CNMSSM) with naturalness priors, which were derived in a previous work. In the past, most Bayesian analyses of the CNMSSM ignored naturalness of the electroweak (EW) scale by making prejudicial assumptions for parameters defined at the EW scale. We test the CNMSSM against the CMSSM with Bayesian evidence, which, with naturalness priors, incorporates a penalty for fine-tuning of the EW scale. With the evidence, we measure credibility with respect to all measurements, including the EW scale and LHC direct searches. We find that the evidence in favor of the CNMSSM versus the CMSSM is “positive” to “strong” but that if one ignores the (Formula presented.)-problem, the evidence is “barely worth mentioning” to “positive”. The (Formula presented.)-problem significantly influences our findings. Unless one considers the (Formula presented.)-problem, the evidence in favor of the CNMSSM versus the CMSSM is at best “positive”, which is two grades below “very strong”. We, furthermore, identify the most probable regions of the CMSSM and CNMSSM parameter spaces and examine prospects for future discovery at hadron colliders. © 2014, The Author(s).

Fowlie A.,Estonian National Institute of Chemical Physics and Biophysics
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014

The absence of supersymmetry or other new physics at the Large Hadron Collider (LHC) has lead many to question naturalness arguments. With Bayesian statistics, we argue that natural models are most probable and that naturalness is not merely an aesthetic principle. We calculate a probabilistic measure of naturalness, the Bayesian evidence, for the Standard Model (SM) with and without quadratic divergences, confirming that the SM with quadratic divergences is improbable. We calculate the Bayesian evidence for the constrained minimal supersymmetric Standard Model (CMSSM) with naturalness priors in three cases: with only the MZ measurement; with the MZ measurement and LHC measurements; and with the MZ measurement, mh measurement and a hypothetical null result from a s=100TeV Very Large Hadron Collider (VLHC) with 3000/fb. The "fine-tuning price" of the VLHC given LHC results would be ∼400, which is slightly less than that of the LHC results given the electroweak scale (∼500). © 2014 American Physical Society.

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