Self-interacting Dark Matter and Invisibly Decaying Higgs

Self-interacting dark matter has been suggested in order to overcome the difficulties of the Cold Dark Matter model on galactic scales. We argue that a scalar gauge singlet coupled to the Higgs boson, which could lead to an invisibly decaying Higgs, is an interesting candidate for this self-interacting dark matter particle. We also present estimates on the abundance of these particles today as well as consequences to non-Newtonian forces.Comment: 4 pages, Revte

The symbiotic binary system RX Puppis: a possible recurrent nova with a Mira companion

We present an analysis of photometric and spectroscopic observations of the symbiotic binary system RX Pup with the aims of developing a reliable binary for the system and identifying mechanisms responsible for its spectacular activity. The binary is composed of a long-perod Mira variable surrounded by a thick dust shell and a hot white dwarf companion. The hot component produces practically all activity observed in the UV, optical and radio range, while variable obscuration of the Mira by circumstellar dust is responsible for long-term changes in the near-IR magnitudes. The observations show RX Pup underwent a nova-like eruption during the last three decades. The hot component contracted in radius at roughly constant luminosity from 1975 to 1986, and was the source of a strong stellar wind which prevented it from accreting material lost in the Mira wind. Around 1988/9 the hot component turned over in the HR diagram and by 1991 its luminosity had faded by a factor of about 30 with respect to the maximum plateau value and the hot wind had practically ceased. By 1995 the nova remnant started to accrete material from the Mira wind, as indicated by a general increase in intensity of the optical continuum and HI emission. The quiescent spectrum resembles the quiescent spectra of symbiotic recurrent novae, and its intensity indicates the hot component must accrete as much as about 1 per cent of the Mira wind, which is more or less the amount predicted by Bondi-Hoyle theory. The earliest observational records from the 1890s suggest that another nova-like eruption of RX Pup occurred around 1894.Comment: 23 pages, 12 figues, MNRAS - accepte

An Unusual Case of Colon Perforation Complicating Acute Pancreatitis

Colonic complications of severe acute pancreatitis occur rarely. Although there have been several theories on how pancreatic pseudocysts rupture into the colon, the exact pathogenesis remains unknown. We report an unusual case of pseudocysts complicating severe acute pancreatitis presenting with colonic perforation in a 71-year-old man with a history of chronic mesenteric ischemia. Pressure effects from a giant pseudocyst and intravascular volume depletion with acute insult on chronic mesenteric ischemia are highlighted as possible etiologic factors

No one is safe! But who’s more susceptible? Locus of control moderates pandemic perceptions’ effects on job insecurity and psychosocial factors amongst MENA hospitality frontliners: a PLS-SEM approach

Background The research aimed to formulate and test a model concerning COVID-19 perceptions effects on job insecurity and a set of psychosocial factors comprising anxiety, depression, job burnout and job alienation in the Middle East and North African (hereafter, MENA) regional context. Also, the study attempted to examine whether locus of control can moderate these hypothesised linkages amongst customer service employees working in MENA hospitality organisations. Methods The study is based on a sample of 885 responses to an online survey and Partial Least Square Structural Equation Modelling (PLS-SEM). Results The main findings show the existence of a significant correlation between COVID perceptions and job insecurity and all psychosocial factors, i.e., more intense COVID-19 perceptions accompany higher levels of job insecurity, anxiety, depression, job burnout and job alienation. Furthermore, our results revealed that, in pandemic time, hospitality customer service employees with external locus of control are more likely to suffer higher alienation, anxiety and depression than those with internal locus of control. Conclusions The research originality centres on the establishment that COVID-19 has a severe negative impact within the hospitality customer service labour force (in the MENA region). These effects were more profound for participants who claimed external locus of control than those with internal locus of control

On a geometrical notion of dimension for partially ordered sets

The well-known notion of dimension for partial orders by Dushnik and Miller allows to quantify the degree of incomparability and, thus, is regarded as a measure of complexity for partial orders. However, despite its usefulness, its definition is somewhat disconnected from the geometrical idea of dimension, where, essentially, the number of dimensions indicates how many real lines are required to represent the underlying partially ordered set. Here, we introduce a variation of the Dushnik-Miller notion of dimension that is closer to geometry, the Debreu dimension, and show the following main results: (i) how to construct its building blocks under some countability restrictions, (ii) its relation to other notions of dimension in the literature, and (iii), as an application of the above, we improve on the classification of preordered spaces through real-valued monotones

Majorization requires infinitely many second laws

In statistical mechanics, the possibility of spontaneous transitions between the different states of an isolated system are usually characterized by the increase of entropy via the second law of thermodynamics. However, a stronger criterion that holds for systems obeying a master equation, the so-called principle of increasing mixing character, has also been proposed to describe these transitions. This principle relies on a more fundamental notion of disorder, which is described through the majorization preorder. Here, we show that, when replacing entropy by disorder, one requires a countably infinite family of entropy-like functions in order to obtain the corresponding second law of thermodynamics. Hence, regarding complexity, disorder goes well beyond the second law of thermodynamics. Furthermore, we prove an analogous result holds for the transitions of a system that is coupled to a heat bath

Classification of preordered spaces in terms of monotones -- Filling in the gaps

Following the recent introduction of new classes of monotones, like injective monotones or strict monotone multi-utilities, we present the classification of preordered spaces in terms of both the existence and cardinality of real-valued monotones and the cardinality of the quotient space. In particular, we take advantage of a characterization of real-valued monotones in terms of separating families of increasing sets in order to obtain a more complete classification consisting of classes that are strictly different from each other

Emission of gamma rays shifted from resonant absorption by electron-nuclear double transitions in ^{151}Eu^{2+}:CaF_2

We show that the emission of a gamma-ray photon by a nucleus can be influenced by a microwave magnetic field acting on the atomic electrons. We study theoretically these electron-nuclear double transitions (ENDTs) for ^{151}Eu nuclei in a CaF_2 lattice at low temperature, in the presence of a static magnetic field and of a microwave magnetic field. The ENDTs acquire a significant intensity for certain resonance frequencies. The ENDTs are of interest for the identification of the position of the lines in complex M\"{o}ssbauer spectra.Comment: 8 pages; 3 Postscript figures: Fig. 1, Fig. 2(a), Fig. 2(b