1,720,984 research outputs found
The bearable lightness of new physics beyond the Standard Model
Full text linkThe absence of new physics signals at the TeV scale has recently triggered a shift of interest towards light and weakly coupled extensions of the Standard Model (SM). We consider a light new physics scenario coupled to the SM fields in a effective theory. Different types of light new physics, searched by present and future experiments at the intensity frontier, are studied and investigated, from sub-GeV abelian gauge vector bosons to right-handed neutrinos at GeV scale. In the former case, we study the dependence on the UV completion of the effective Wess-Zumino terms that appears in the IR theory when gauge bosons are coupled to a SM current whose conservation is broken at loop level. We show how to avoid the would be strong constraints of energy enhanced process due to flavor changing neutral current generated by the Wess-Zumino terms. In the latter case, we work in a minimal see-saw scenario with two right-handed neutrinos with mass at the GeV scale and highlight the prospects for testing the decay induced by an effective dipole operator at future facilities targeting long-lived particles such as the SHiP experiment. In the last part of the thesis, we critically re-examine the new particle interpretation of recent experimental anomalies observed in nuclear transition from the ATOMKI collaboration. Indeed, the hypothetical particle, denoted as and proposed by the collaboration itself, would be a light and weakly-interacting boson and we employ a multipole expansion to estimate the nucleon coupling to the light state, identifying the axial vector state as the most promising candidate. Intensity-frontier experiments like MEG II and PADME will probe the ATOMKI anomaly in the near future
An updated view on the ATOMKI nuclear anomalies
Full text linkIn view of the latest experimental results recently released by the ATOMKI
collaboration, we critically re-examine the possible theoretical interpretation
of the observed anomalies in terms of a new BSM boson with mass
MeV. To this end we employ a multipole expansion method and give an
estimate for the range of values of the nucleon couplings to the new light
state in order to match the experimental observations. Our conclusions identify
the axial vector state as the most promising candidate, while other spin/parity
assignments seems disfavored for a combined explanation. This results is
however based on an order of magnitude estimate for the, currently unknown,
axial nuclear matrix element of the C transition, that needs then to be
evaluated before being able to draw a definite conclusion. Intriguingly, an
axial vector state can also simultaneously accommodate other experimental
anomalies, {\emph{i.e.}} the KTeV anomaly in decay while
being compatible with the conflicting measurements of the anomalous magnetic
moment of the electron and other constraints on the electron
couplings of the boson. The PADME experiment will completely cover the
relevant region of the parameter space, thus allowing for a strong test of the
existence of the particle.Comment: 42 pages, 9 figures, matches published version and erratum (results
unchanged
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
Perturbative unitarity constraints on generic vector interactions
Full text linkAbstract We study perturbative unitarity constraints on generic interactions between fermion and vector fields, which are allowed to have generic quantum numbers under a Π i SU(N i ) ⨂ U(1) group. We derive compact expressions for the bounds on the couplings for the cases where the fields transform under the trivial, fundamental or adjoint representation of the various, considering both the case of a complex vector arbitrary interactions with fermionic current and also the case of vectors arising as gauge fields. We apply our results to some specific NP models showing the constraints that can be derived using the tool of perturbative unitarity
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Probing right-handed neutrinos dipole operators
Full text linkWe consider the minimal see-saw extension of the Standard Model with two
right-handed singlet fermions with mass at the GeV scale, augmented
by an effective dipole operator between the sterile states. We firstly review
current bounds on this effective interaction from fixed-target and collider
experiments as well as from astrophysical and cosmological observations. We
then highlight the prospects for testing the decay induced
by the dipole at future facilities targeting long lived particles such as
ANUBIS, CODEX-b, FACET, FASER 2, MAPP and SHiP.Comment: 24 pages, 3 figures, matches published versio
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