1,721,046 research outputs found
The recent gravitational wave observation by pulsar timing arrays and primordial black holes: the importance of non-gaussianities
Full text linkWe study whether the signal seen by pulsar timing arrays (PTAs) may originate
from gravitational waves (GWs) induced by large primordial perturbations. Such
perturbations may be accompanied by a sizeable primordial black hole (PBH)
abundance. We improve existing analyses and show that PBH overproduction
disfavors Gaussian scenarios for scalar-induced GWs at 2{\sigma} and
single-field inflationary scenarios, accounting for non-Gaussianity, at
3{\sigma} as the explanation of the most constraining NANOGrav 15-year data.
This tension can be relaxed in models where non-Gaussianites suppress the PBH
abundance. On the flip side, the PTA data does not constrain the abundance of
PBHs.Comment: V3: Version published on PRL. 15 pages and 8 figures. Full article +
supplementary materials. V1 appeared on Thu, 29 Jun 202
A la recerca d'ones gravitacionals a partir de la formació de forats negres primordials
No full textEls components de la matèria fosca continuen sent desconeguts, però els forats negres primordials i els productes d'evaporació són candidats interessants. Investigadors de l'IFAE i del King's College London han buscat traces d'aquests forats negres a les dades del detector d'ones gravitacionals. Aquestes traces no es van trobar, però s'espera que els detectors d'ones gravitacionals de propera generació puguin provar aquest escenari.Los componentes de la materia oscura siguen siendo desconocidos, pero los agujeros negros primordiales y sus productos de evaporación son candidatos interesantes. Investigadores del IFAE y del King's College London han buscado trazas de estos agujeros negros en los datos del detector de ondas gravitacionales. No se encontraron tales trazas, pero se espera que los detectores de ondas gravitacionales de próxima generación puedan probar este escenario.The constituents of dark matter remain unknown, but primordial black holes and their evaporation products are interesting candidates. IFAE and King's College London researchers have searched signatures of these black holes in gravitational wave detector data. No such signatures were found but it is hoped that the next generation gravitational wave detectors will be able to test this scenario
Dark matter and baryogenesis in Higgs portal models
No full textThis work focuses on two of the main issues in current understanding of
particle physics described by the Standard Model. The Standard Model,
despite of its success, is not complete. Existence of dark matter has been
clearly verified, but its nature is unknown. Also, the baryon asymmetry in
the Universe hints that the Standard Model has to be extended. In this thesis
we study Higgs portal models which both contain dark matter candidates,
and can provide for a successful production of the baryon asymmetry.unknown accessibilityei tietoa saavutettavuudest
Venture capital firm reputation, portfolio company long-run performance, hot IPO markets, and different countries - evidence from continental Europe’s market for initial public offerings
No full textUsing a sample of 442 initial public offerings, I study the relation of venture capital firm reputation and portfolio company long-run post- initial public offering performance in continental Europe between 2004 and 2016. Inconsistent with Krishnan et al. (2011), I find venture capital reputation, based on past IPO activity of venture capitalists, to have a significant negative relation on issuer long-run performance in Europe. My findings also indicate that venture capital reputation only affects portfolio companies long-run returns negatively in normal markets and is insignificant during hot IPO markets. Also, reputable venture capitalists’ portfolio firm long-run performance is not consistent between my sample countries, but rather reputable venture capitalists’ portfolio companies outperform their constituents in countries with small venture capital markets
Extensions of the standard model scalar sector and constraints from ccolliders and cosmology
No full textIn this thesis we study the Higgs sector of the Standard Model and compare it to the latest data from the LHC and Tevatron experiments. Then we consider two extensions of the Higgs sector. First we extend the Standard Model Higgs sector with one real SU(2) singlet and then we consider two-Higgs- doublet model and extend also it with one real singlet. In both extensions the singlet scalar is considered as a potential dark matter candidate. We find that the parameter space of the so called two-Higgs-doublet-inert-singlet model includes regions which could provide a dark matter candidate which constitutes significant amount of the total dark matter mass density.unknown accessibilityei tietoa saavutettavuudest
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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