1,721,219 research outputs found
Dark matter from an even lighter QCD axion: trapped misalignment
Full text linkWe show that dark matter can be accounted for by an axion that solves the strong CP problem, but is much lighter than usual due to a symmetry. The whole mass range from the canonical QCD axion down to the ultra-light regime is allowed, with . This includes the first proposal of a 'fuzzy dark matter' QCD axion with eV. A novel misalignment mechanism occurs - trapped misalignment - due to the peculiar temperature dependence of the axion potential. The dark matter relic density is enhanced because the axion field undergoes two stages of oscillations: it is first trapped in the wrong minimum, which effectively delays the onset of true oscillations. Trapped misalignment is more general than the setup discussed here, and may hold whenever an extra source of Peccei-Quinn breaking appears at high temperatures. Furthermore, it will be shown that trapped misalignment can dynamically source the recently proposed kinetic misalignment mechanism. All the parameter space is within tantalizing reach of the experimental projects for the next decades. For instance, even Phase I of CASPEr-Electric could discover this axion
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
Quantum corrected black holes from string T-duality
No full textIn this letter we present some stringy corrections to black hole spacetimes emerging from string T-duality. As a first step, we derive the static Newtonian potential by exploiting the relation between the T-duality and the path integral duality. We show that the intrinsic non-perturbative nature of stringy corrections introduces an ultraviolet cutoff known as zero-point length in the path integral duality literature. As a result, the static potential is found to be regular. We use this result to derive a consistent black hole metric for the spherically symmetric, electrically neutral case. It turns out that the new spacetime is regular and is formally equivalent to the Bardeen metric, apart from a different ultraviolet regulator. On the thermodynamics side, the Hawking temperature admits a maximum before a cooling down phase towards a thermodynamically stable end of the black hole evaporation process. The findings support the idea of universality of quantum black holes
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
Probing axions with the neutrino signal from the next Galactic supernova
No full textWe study the impact of axion emission in simulations of massive star explosions, as an additional source of energy loss complementary to the standard neutrino emission. The inclusion of this channel shortens the cooling time of the nascent protoneutron star and hence the duration of the neutrino signal. We treat the axion-matter coupling strength as a free parameter to study its impact on the protoneutron star evolution as well as on the neutrino signal. We furthermore analyze the observability of the enhanced cooling in current and next-generation underground neutrino detectors, showing that values of the axion mass eV can be probed. Therefore a galactic supernova neutrino observation would provide a valuable possibility to probe axion masses in a range within reach of the planned helioscope experiment the International Axion Observatory (IAXO)
Axions in the Presence of Gauge Theories Beyond the Standard Model
No full textNon-supersymmetric Grand Unified models have all the ingredients to solve several fundamental problems of particle physics and cosmology -- neutrino masses and mixing, baryogenesis, the non-observation of strong CP violation, dark matter, inflation -- in one stroke. The axion -- the pseudo Nambu-Goldstone boson arising from the spontaneous breaking of the Peccei-Quinn symmetry -- is the prime dark matter candidate in this setup. We work out the constraints imposed on the axion mass by gauge coupling unification. We also discuss the cosmological and phenomenological implications.\\We consider the described models in the larger context set by combining the Peccei-Quinn symmetry with new gauge symmetries in different ways. We classify the relevant models and give a general procedure by which the physical axion must be identified. Additionally, we apply this procedure to multiple examples. Finally, we discuss the possibility of obtaining the Peccei-Quinn symmetry as an accidental symmetry
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
Revisiting the SN1987A gamma-ray limit on ultralight axion-like particles
Full text linkpeer reviewedWe revise the bound from the supernova SN1987A on the coupling of ultralight axion-like particles (ALPs) to photons. In a core-collapse supernova, ALPs would be emitted via the Primakoff process, and eventually convert into gamma rays in the magnetic field of the Milky Way. The lack of a gamma-ray signal in the GRS instrument of the SMM satellite in coincidence with the observation of the neutrinos emitted from SN1987A therefore provides a strong bound on their coupling to photons. Due to the large uncertainty associated with the current bound, we revise this argument, based on state-of-the-art physical inputs both for the supernova models and for the Milky-Way magnetic field. Furthermore, we provide major amendments, such as the consistent treatment of nucleon-degeneracy effects and of the reduction of the nuclear masses in the hot and dense nuclear medium of the supernova. With these improvements, we obtain a new upper limit on the photon-ALP coupling: g_{a\gamma} < 5.3 x 10^{-12} GeV^{-1}, for m_a < 4.4 x 10^{-10} eV, and we also give its dependence at larger ALP masses. Moreover, we discuss how much the Fermi-LAT satellite experiment could improve this bound, should a close-enough supernova explode in the near future
Electric-magnetic duality invariance implications for axion physics
No full textAxions and axion-like particles are very well-motivated candidates for physics beyond the Standard model, which can be probed by multiple existing and projected experiments and astrophysical observations. Theoretical determination of the relevant low energy axion interactions is essential for guiding the corresponding experimental and observational efforts. In this thesis, we revisit the previous theoretical investigations in this direction. In particular, we show that, contrary to assertions in the literature, the main contribution to the axion-photon coupling need not be quantized in units proportional to . We discuss a loophole in the argument for this quantization and then provide explicit counterexamples. Based on this, we construct a generic axion-photon effective Lagrangian and find that the axion-photon coupling may be dominated by previously unknown Wilson coefficients. We show that this result implies a significant modification of conventional axion electrodynamics and sets new targets for axion experiments. We find that the electromagnetic interactions of axions can violate the CP symmetry and that future experiments could be sensitive to the corresponding coupling. At the core of our theoretical analysis lies a critical reexamination of the interactions between axions and magnetic monopoles. We develop the effective field theory approach to the Zwanziger theory of quantum electromagnetodynamics and show that, contrary to claims in the literature, magnetic monopoles need not give mass to axions. Moreover, we find that a future detection of an axion or axion-like particle with certain parameters can serve as evidence for the existence of magnetically charged matter.Besides studying the structure of the low energy axion interactions in the effective field theory approach, we explicitly construct new theoretical models for the axion which realize the newly found interactions. In these models, the PQ mechanism is realized through a coupling of the Peccei-Quinn complex scalar field to magnetically charged fermions at high energies. We consider both the cases of Abelian and non-Abelian magnetic charges. We show that these models indeed solve the strong CP problem and then integrate out heavy magnetic monopoles using the Schwinger proper time method. We find that the models discussed yield axion couplings to the Standard Model which are drastically different from the ones calculated within the KSVZ/DFSZ-type models. As a consequence, large part of the corresponding parameter space can be probed by various projected experiments. Moreover, the axion we introduce is consistent with the astrophysical hints for axions suggested both by the anomalous TeV-transparency of the Universe and by the excessive cooling of horizontal branch stars in globular clusters. We argue that the leading term for the cosmic axion abundance is not changed compared to the conventional pre-inflationary scenario for an axion decay constant
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