Variación espacial de las constantes fundamentales: comparación entre los modelos fenomenológicos y distancias luminosas de supernovas tipo Ia

El Modelo Estándar y la Relatividad General son las teorías que explican, con gran éxito, los fenómenos físicos a bajas energías. Las ecuaciones de dichas teorías involucran ciertos parámetros que tienen la particularidad de permanecer invariantes en el espacio-tiempo. Son las llamadas constantes fundamentales. Desde la hipótesis de Dirac en 1937, según la cual, las constantes fundamentales son simples funciones de la edad del Universo; la variación temporal y espacial de dichas constantes ha sido objeto de numerosos trabajos de investigación. El interés teórico en este tema proviene del hecho de que varias de las teorías que intentan unificar las cuatro interacciones fundamentales de la Física tienen diferentes predicciones para la variación de estos parámetros. Los datos observacionales y experimentales cumplen un rol muy importante ya que nos permiten testear la validez de estas teorías al establecer límites sobre la variación de las constantes fundamentales. La investigación experimental comprende desde mediciones en laboratorio hasta datos de origen cosmológico. La mayoría de los resultados obtenidos son consistentes con una variación nula de las constantes fundamentales. En los últimos años, Webb y colaboradores propusieron el denominado método de los muchos multipletes para analizar observaciones de quásares de alto corrimiento al rojo, obteniendo como resultado una variación no nula de la constante de estructura fina α. Para poder explicar los datos obtenidos propusieron una variación espacial de α de tipo dipolar. De ser cierta esta variación, debería tener consecuencias en las luminosidades medidas de las Supernovas Tipo Ia (SNIa). Esto se debe a que la luminosidad máxima alcanzada en la explosión depende de α a través de la opacidad de la atmósfera en expansión y de la energía liberada. La importancia de las SNIa radica en que pueden ser utilizadas como candelas estándar debido a su notable homogeneidad. En este trabajo se utilizan las distancias luminosas de Supernovas tipo Ia (SNIa) con el fin de testear el modelo fenomenológico dipolar propuesto por Webb y colaboradores. Para ello, se realiza un análisis estadístico con el objetivo de contrastar los valores observacionales de las distancias luminosas con las predicciones teóricas del modelo dipolar. Éstas se calculan introduciendo una modificación debida a la posible variación de α. Por otro lado, se utilizan estos mismos datos para realizar un análisis estadístico obteniendo nuevos parámetros para el modelo dipolar, verificando luego su consistencia con aquellos obtenidos a partir de las observaciones de quásares. Los resultados indican que los datos de SNIa actuales no permiten distinguir entre un modelo con variación de espacial de α de tipo dipolar y el Modelo Estándar donde α no varía. También se concluye la inconsistencia entre los parámetros de dipolo obtenidos a partir de las observaciones de SNIa con los que se obtuvieron a partir de las observaciones de quásares. Por último, se realiza una primera estimación para una posible variación espacial de tipo dipolar, tanto de la velocidad de la luz c como de β = h*c, con h la constante de Planck reducida; añadiendo además en estos casos la dependencia de la masa de Chandrasekhar con dichas constantes.The large-number hypothesis conjectures that fundamental constants may vary. Accordingly, the space-time variation of fundamental constants has been an active subject of research for decades. Recently, using data obtained with large telescopes a phenomenological model in which the fine structure constant might vary spatially has been proposed. In this work, we test whether this hypothetical spatial variation of , which follows a dipole law, is compatible with the data of distant thermonuclear type Ia supernovae. Unlike previous works, in our calculations we consider not only the variation of the luminosity distance when a varying is adopted, but we also take into account the variation of the peak luminosity of Type Ia supernovae resulting from a variation of . We find that there is no significant difference between the several phenomenological models studied here and the standard one, in which does not vary spatially. We conclude that the present set of data of Type Ia supernovae is not able to distinguish the standard model from the dipole models, and thus cannot be used to discard nor to confirm the proposed spatial variation of . Also, we carry out a first estimation of the possible spatial variation of speed of light c and = ¯hc, where ¯h is the reduced Planck constant.Facultad de Ciencias Astronómicas y Geofísica

Variación espacial de las constantes fundamentales: comparación entre los modelos fenomenológicos y distancias luminosas de supernovas tipo Ia

El Modelo Estándar y la Relatividad General son las teorías que explican, con gran éxito, los fenómenos físicos a bajas energías. Las ecuaciones de dichas teorías involucran ciertos parámetros que tienen la particularidad de permanecer invariantes en el espacio-tiempo. Son las llamadas constantes fundamentales. Desde la hipótesis de Dirac en 1937, según la cual, las constantes fundamentales son simples funciones de la edad del Universo; la variación temporal y espacial de dichas constantes ha sido objeto de numerosos trabajos de investigación. El interés teórico en este tema proviene del hecho de que varias de las teorías que intentan unificar las cuatro interacciones fundamentales de la Física tienen diferentes predicciones para la variación de estos parámetros. Los datos observacionales y experimentales cumplen un rol muy importante ya que nos permiten testear la validez de estas teorías al establecer límites sobre la variación de las constantes fundamentales. La investigación experimental comprende desde mediciones en laboratorio hasta datos de origen cosmológico. La mayoría de los resultados obtenidos son consistentes con una variación nula de las constantes fundamentales. En los últimos años, Webb y colaboradores propusieron el denominado método de los muchos multipletes para analizar observaciones de quásares de alto corrimiento al rojo, obteniendo como resultado una variación no nula de la constante de estructura fina α. Para poder explicar los datos obtenidos propusieron una variación espacial de α de tipo dipolar. De ser cierta esta variación, debería tener consecuencias en las luminosidades medidas de las Supernovas Tipo Ia (SNIa). Esto se debe a que la luminosidad máxima alcanzada en la explosión depende de α a través de la opacidad de la atmósfera en expansión y de la energía liberada. La importancia de las SNIa radica en que pueden ser utilizadas como candelas estándar debido a su notable homogeneidad. En este trabajo se utilizan las distancias luminosas de Supernovas tipo Ia (SNIa) con el fin de testear el modelo fenomenológico dipolar propuesto por Webb y colaboradores. Para ello, se realiza un análisis estadístico con el objetivo de contrastar los valores observacionales de las distancias luminosas con las predicciones teóricas del modelo dipolar. Éstas se calculan introduciendo una modificación debida a la posible variación de α. Por otro lado, se utilizan estos mismos datos para realizar un análisis estadístico obteniendo nuevos parámetros para el modelo dipolar, verificando luego su consistencia con aquellos obtenidos a partir de las observaciones de quásares. Los resultados indican que los datos de SNIa actuales no permiten distinguir entre un modelo con variación de espacial de α de tipo dipolar y el Modelo Estándar donde α no varía. También se concluye la inconsistencia entre los parámetros de dipolo obtenidos a partir de las observaciones de SNIa con los que se obtuvieron a partir de las observaciones de quásares. Por último, se realiza una primera estimación para una posible variación espacial de tipo dipolar, tanto de la velocidad de la luz c como de β = h*c, con h la constante de Planck reducida; añadiendo además en estos casos la dependencia de la masa de Chandrasekhar con dichas constantes.The large-number hypothesis conjectures that fundamental constants may vary. Accordingly, the space-time variation of fundamental constants has been an active subject of research for decades. Recently, using data obtained with large telescopes a phenomenological model in which the fine structure constant might vary spatially has been proposed. In this work, we test whether this hypothetical spatial variation of , which follows a dipole law, is compatible with the data of distant thermonuclear type Ia supernovae. Unlike previous works, in our calculations we consider not only the variation of the luminosity distance when a varying is adopted, but we also take into account the variation of the peak luminosity of Type Ia supernovae resulting from a variation of . We find that there is no significant difference between the several phenomenological models studied here and the standard one, in which does not vary spatially. We conclude that the present set of data of Type Ia supernovae is not able to distinguish the standard model from the dipole models, and thus cannot be used to discard nor to confirm the proposed spatial variation of . Also, we carry out a first estimation of the possible spatial variation of speed of light c and = ¯hc, where ¯h is the reduced Planck constant.Facultad de Ciencias Astronómicas y Geofísica

Spatial variation of fundamental constants: testing models with thermonuclear supernovae

Since Dirac stated his Large Number Hypothesis the space-time variation of fundamental constants has been an active subject of research. Here we analyze the possible spatial variation of two fundamental constants: the fine structure constant {\alpha} and the speed of light c. We study the effects of such variations on the luminosity distance and on the peak luminosity of Type Ia supernovae (SNe Ia). For this, we consider the change of each fundamental constant separately and discuss a dipole model for its variation. Elaborating upon our previous work, we take into account the variation of the peak luminosity of Type Ia supernovae resulting from the variation of each of these fundamental constants. Furthermore, we also include the change of the energy release during the explosion, which was not studied before in the literature. We perform a statistical analysis to compare the predictions of the dipole model for {\alpha} and c variation with the Union2.1 and JLA compilations of SNe Ia. For this, we also allow the nuisance parameters of the distance estimator $\mu_0$ and the cosmological density matter $\Omega_m$ to vary. As a result of our analysis we obtain a first estimate of the possible spatial variation of the speed of light c. On the other hand, we find that there is no significant difference between the several phenomenological models studied here and the standard cosmological model, in which fundamental constants do not vary at all. Thus, we conclude that the actual set of data of Type Ia supernovae does not allow to verify the hypothetical spatial variation of fundamental constants.Comment: 20 pages, 3 figures. Accepted for publication in IJMP

Testing modified gravity theory (MOG) with type Ia supernovae, cosmic chronometers and baryon acoustic oscillations

We analyse the MOdified Gravity (MOG) theory, proposed by Moffat, in a cosmological context. We use data from Type Ia Supernovae (SNe Ia), Baryon Acoustic Oscillations (BAO) and Cosmic Chronometers (CC) to test MOG predictions. For this, we perform χ2 tests considering fixed values of H0 and VG, the self-interaction potential of one of the scalar fields in the theory. Our results show that the MOG theory is in agreement with all data sets for some particular values of H0 and VG, being the BAO data set the most powerful tool to test MOG predictions, due to its constraining power.Fil: Negrelli, Carolina Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Kraiselburd, Lucila. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Landau, Susana Judith. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; ArgentinaFil: Scoccola, Claudia Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentin

Associação entre acantose nigricans e insulinorresistência em adolescentes com excesso de peso

Tese de mestrado, Saúde do Adolescente, Universidade de Lisboa, Faculdade de Medicina, 2017Introdução: A obesidade infanto-juvenil representa um grave problema de saúde pública da atualidade. De entre as comorbilidades mais prevalentes estão a insulinorresistência (IR) e a síndrome metabólica (SM), intimamente ligadas entre si. A Acantose nigricans (AN) é uma dermatose hiperpigmentada facilmente identificável que está associada a obesidade e diabetes. No entanto, são escassos os estudos em idade pediátrica que fazem a associação entre AN, IR e SM. Objetivos: O principal objetivo do estudo é determinar se existe relação entre o grau de AN, de acordo com a escala de Burke et al., e a presença de IR e de SM numa população de adolescentes com idade entre os 12 e os 18 anos com excesso de peso seguidos na Consulta de Obesidade Pediátrica do Departamento de Pediatria do Hospital de Santa Maria. Metodologia: Estudo descritivo, transversal e correlacional. O tipo de amostragem foi não probabilística e a técnica de amostragem foi de conveniência. Foram colhidos dados clínicos e laboratoriais relativos aos critérios incluídos na definição de SM de acordo com o International Diabetes Federation (IDF) de 2007 e o índice de IR foi calculado com base no Homeostasis Model Assessment – Insulin resistance (HOMA-IR). O índice de AN foi calculado com base na soma das pontuações atribuídas na aplicação da escala de AN de Burke et al completa. Resultados: Obtiveram-se dados de 79 adolescentes, 49,4% do sexo feminino. Todos tinham obesidade ou excesso de peso. Sessenta e nove adolescentes (87,3%) tinham algum grau de AN. Nove doentes (11,4%) cumpriam critérios para SM. Constatou-se uma associação entre AN axila/AN pescoço textura/índice de AN (p < 0,05) e o z-score de índice de massa corporal (IMC). Verificou-se existir uma associação com forte significado estatístico entre AN pescoço gravidade (p < 0,001) e textura (p = 0,002) e HOMAIR/ insulinemia e também entre AN axila (p = 0,018) e insulinemia. Verificou-se igualmente uma correlação estatisticamente significativa entre o índice de AN e a insulinemia (p < 0,01) e o índice de AN e o HOMA-IR (p < 0,05), mesmo após controlo para o IMC. No entanto, a força da associação entre AN pescoço gravidade/AN axila e IR foi superior à do índice AN e IR. Não se verificou relação estatisticamente significativa entre AN e SM. Conclusão: A aplicação da escala de AN proposta por Burke et al. na consulta de obesidade pediátrica revelou-se útil, pela associação fortemente significativa que se verificou entre a AN, o IMC e a IR. No entanto, parece apenas justificar-se a aplicação dos três primeiros itens da escala (AN pescoço gravidade,axila e textura pescoço) por rotina. A avaliação da AN permitiu assim uma fácil identificação de adolescentes obesos com IR, logo em risco de desenvolver SM e mesmo diabetes mellitus tipo II no futuro. Desta forma, estes adolescentes não necessitam de fazer controlos analíticos tão frequentes, poupando-se recursos. Não se encontrou uma relação entre AN e SM, talvez pela idade jovem da amostra e o diminuto número de casos identificados de SM. São necessários estudos aleatorizados que venham comprovar estes resultados, no sentido de tirar o máximo partido da utilização da escala de Burke et al.Introduction: Infantile and juvenile obesity is a very important public health issue. Among the most prevalent comorbidities associated with obesity are insulin resistance (IR) and metabolic syndrome (MS), intimatelly related. Acanthosis nigricans (AN) is a hyerpigmented dermatosis easily identified which is currently associated with obesity and diabetes. However, studies that relate AN with IR and MS in the pediatric population are sparse. Aims: The main aim of the study is to find a relation between the degree of AN according to Burke´s proposed scale and the presence of IR as well as MS in a group of overweight adolescents between 12 and 18 years old attending the pediatric obesity consultation, Pediatric`s Department, Santa Maria`s Hospital. Methods: This is a cross-sectional descriptive and correlational study. Non probabilistic and convenience sampling was used. Clinical and laboratorial data was collected according to the International Diabetes Federation (IDF) 2007 criteria for MS in children and adolescents. The índex of IR was calculated based on the Homeostasis Model Assessment – Insulin resistance (HOMA-IR). The AN score was calculated based on the sum of given punctuation after applying Burke`s AN complete scale. Results: seventy-nine adolescents were recruited, 49,4% of which were female. All of them were obese or overweight. Sixty-nine adolescents (87,3%) had some degree of AN. Nine adolescents (11,4%) met criteria for MS. There was a statistically significant correlation between AN axilla/AN neck texture/AN score and body mass index (BMI) zscore (p < 0,05). A strong association between AN neck severity (p < 0,001) and texture (p = 0,002) and HOMA-IR/insulin was seen, as well as between AN axilla (p = 0,018) and insulin. There was also a statistically significant correlation between the AN score and insulin level (p < 0,01) as well as HOMA-IR (p < 0,05), after adjusting for BMI. However the strength of the association between AN neck severity and axilla with IR was higher than between degree of AN and IR. There was no statistically significant relation between AN and MS. Conclusions: Using the scale proposed by Burke et al, this study revealed its utility as tthere was a strong association between AN, BMI and IR. However, it seems that only the three first itens of the scale (AN neck severity, axilla and neck texture) should be applied routinely. In this way, it seems easier to identify adolescents with IR, who are, therefore, at risk for developing diabetes type II and MS in the future. On the other hand, these adolescents don´t have to do as frequent analytic controls, with consequent resource savings. However, there was not a statistically significant relation between AN and MS, maybe because the population was too young and there were few identified adolescents with MS. Further randomized investigations are needed in order to ascertain whether AN and MS are related, so that the best use of Burke`s AN scale can be made

Aproximación a las representaciones sociales sobre la enseñanza de una lengua extranjera

La presente comunicación describe las acciones efectuadas en el marco de una investigación en desarrollo, impulsada por la DGES de la provincia de Córdoba, que tiene por objetivo caracterizar el perfil de docente que se construye en el imaginario colectivo de quienes se preparan, en institutos de formación superior, para ser profesores de inglés en el nivel medio.Desde la perspectiva de Moscovici (1979) y Jodelet (1985), se analizan las representaciones sociales sobre la enseñanza de la lengua inglesa (es decir, las creencias, actitudes y opiniones sobre la educación lingüística en inglés), a fin de recabar información significativa para la toma de decisiones áulicas, curriculares e institucionales en lo relativo a la formación profesional.Específicamente, las representaciones se estudian en alumnos que cursan la carrera de profesorado de inglés en el "IFD Nuestra Señora del Sagrado Corazón‟ (Córdoba capital).En un nivel descriptivo de investigación y desde un enfoque cualitativo, se instrumentan técnicas, tales como la historia de vida, la observación no participante y la carta asociativa (Abric, 2001), para la recolección del contenido y la estructura representacional del objeto considerado.En este trabajo, además de un abordaje en detalle del modo como se han elaborado estos instrumentos, se propone una discusión preliminar de los datos obtenidos, a partir de las historias de vida, cuyo análisis da cuenta de que, para el futuro docente, la enseñanza del inglés parece delinearse en la oposición público/privado, en las determinaciones de un contexto desfavorable y en los obstáculos para conducir la enseñanza en lengua extranjera, entre otros aspectos

Solar System tests and chameleon effect in f (R) gravity

Using a novel and self-consistent approach that avoids the scalar-tensor identification in the Einstein frame, we reanalyze the viability of f(R) gravity within the context of solar-system tests. In order to do so, we depart from a simple but fully relativistic system of differential equations that describe a compact object in a static and spherically symmetric spacetime, and then we make suitable linearizations that apply to nonrelativistic objects such as the Sun. We then show clearly under which conditions the emerging chameleonlike mechanism can lead to a post-Newtonian parameter {\gamma} compatible with the observational bounds. To illustrate this method, we use several specific f(R) models proposed to explain the current acceleration of the Universe, and we show which of them are able to satisfy those bounds.Comment: accepted in Phys. Rev.

Spatial variation of fundamental constants: testing models with thermonuclear supernovae

Since Dirac stated his Large Number Hypothesis the space-time variation of fundamental constants has been an active subject of research. Here we analyze the possible spatial variation of two fundamental constants: the fine structure constant α and the speed of light c. We study the effects of such variations on the luminosity distance and on the peak luminosity of Type Ia supernovae (SNe Ia). For this, we consider the change of each fundamental constant separately and discuss a dipole model for its variation. Elaborating upon our previous work, we take into account the variation of the peak luminosity of Type Ia supernovae resulting from the variation of each of these fundamental constants. Furthermore, we also include the change of the energy release during the explosion, which was not studied before in the literature. We perform a statistical analysis to compare the predictions of the dipole model for α and c variation with the Union 2.1 and JLA compilations of SNe Ia. Allowing the nuisance parameters of the distance estimator μ0 and the cosmological density matter Ωm to vary. As a result of our analysis, we obtain a first estimate of the possible spatial variation of the speed of light c. On the other hand, we find that there is no significant difference between the several phenomenological models studied here and the standard cosmological model, in which fundamental constants do not vary at all. Thus, we conclude that the actual set of data of Type Ia supernovae does not allow to verify the hypothetical spatial variation of fundamental constants.Facultad de Ciencias Astronómicas y Geofísica

The variation of the fine structure constant: testing the dipole model with thermonuclear supernovae

The large-number hypothesis conjectures that fundamental constants may vary. Accordingly, the space-time variation of fundamental constants has been an active subject of research for decades. Recently, using data obtained with large telescopes a phenomenological model in which the fine structure constant might vary spatially has been proposed. We test whether this hypothetical spatial variation of α, which follows a dipole law, is compatible with the data of distant thermonuclear supernovae. Unlike previous works, in our calculations we consider not only the variation of the luminosity distance when a varying α is adopted, but we also take into account the variation of the peak luminosity of Type Ia supernovae resulting from a variation of α. This is done using an empirical relation for the peak bolometric magnitude of thermonuclear supernovae that correctly reproduces the results of detailed numerical simulations. We find that there is no significant difference between the several phenomenological models studied here and the standard one, in which α does not vary spatially. We conclude that the present set of data of Type Ia supernovae is not able to distinguish the standard model from the dipole models, and thus cannot be used to discard nor to confirm the proposed spatial variation of α.Facultad de Ciencias Astronómicas y Geofísica

First results of the glitching pulsars monitoring program at the Argentine Institute of Radioastronomy

We report here on the first results of a systematic monitoring of southern glitching pulsars at the Argentine Institute of Radio astronomy started on the year 2019. We detected a major glitch in the Vela pulsar (PSR J0835$-$4510) and two mini-glitches in PSR J1048$-$5832. For each glitch, we present the measurement of glitch parameters by fitting timing residuals. We then make an individual pulses study of Vela in observations previous and after the glitch. We selected 6 days of observations around the major glitch on July 22nd 2021 and study their statistical properties with machine learning techniques. We use Variational AutoEncoder (VAE) reconstruction of the pulses to separate them clearly from the noise. We perform a study with Self-Organizing Maps (SOM) clustering techniques and find an unusual behavior of the clusters two days prior to the glitch. This behavior is only visible in the the higher amplitude pulse clusters and if intrinsic to the pulsar could be interpreted as a precursor of the glitch.Comment: 13 pages, 13 figures, 13 table