Number of entries: **38**

### Inflationary universe in 𝐹(𝑅) gravity with antisymmetric tensor fields and their suppression during its evolution

**Start:** 11:00h

**Speaker:** Tanmoy Paul

**Place:** Alberto Lobo Room

**Start:** 11:00h

**Speaker:** Tanmoy Paul

**Place:** Alberto Lobo Room

The intriguing question, why the present scale of the universe is free from any perceptible footprints of rank-2 antisymmetric tensor fields (generally known as Kalb-Ramond fields), is addressed. A quite natural explanation of this issue is given from the angle of higher-curvature gravity, both in four- and in five-dimensional spacetime. The results here obtained reveal that the amplitude of the Kalb-Ramond field may be actually large and playa significant role during the early universe, while the presence of higher-order gravity suppresses this field during the cosmological evolution, so that it eventually becomes negligible in the current universe. Besides the suppression of the Kalb-Ramond field, the extra degree of freedom in F(R) gravity, usually known as scalaron, also turns out to be responsible for inflation. Such F(R) gravity with Kalb-Ramond fields may govern the early universe to undergo an inflationary stage at early times (with the subsequent graceful exit) for a wider range of F(R) gravity than without antisymmetric fields. Furthermore, the models—in four-and five-dimensional spacetimes—are linked to observational constraints, with the conclusion that the corresponding values of the spectral index and tensor-to-scalar ratio closely match the values provided by the Planck survey 2018 data.
### Dark Matter and Dark Energy from a New Nonlocal Modified Gravity

**Start:** 12:00h

**Speaker:** Branko Dragovich (Institute of Physics, University of Belgrade, Belgrade, Serbia)

**Place:** Alberto Lobo Room

**Start:** 12:00h

**Speaker:** Branko Dragovich (Institute of Physics, University of Belgrade, Belgrade, Serbia)

**Place:** Alberto Lobo Room

I will present some exact cosmological solutions for modified gravity based on a nonlocal operator acting between two factors of the square root of R â€“ 2 Lambda. One of these solutions imitates properties similar to an interplay of the dark matter and the dark energy. For this solution, we computed some cosmological parameters which are in a good agreement with observations. This talk is based on a recent paper published in Phys. Lett. B.
### Studying the Expansion of the Universe with quasar spectra

**Start:** 12:00h

**Speaker:** Andreu Font Ribera (University College London)

**Place:** Sala Alberto Lobo

**Start:** 12:00h

**Speaker:** Andreu Font Ribera (University College London)

**Place:** Sala Alberto Lobo

From 2009 to 2014, the Baryon Oscillation Spectroscopic Survey (BOSS) used the SDSS telescope to obtain spectra of 1.5 million galaxies to get very accurate measurements of the Baryon Acoustic Oscillations (BAO) scale at redshift z ~0.5. At the same time, BOSS observed over 184 000 high redshift quasars (z>2.15) with the goal of detecting the BAO feature in the clustering of the intergalactic medium, using a technique known as the Lyman alpha forest (LyaF).

In this talk I will overview the final results from the LyaF working group in BOSS, and I will present updated results obtained with the extended BOSS survey (eBOSS, 2014-2019). This include the measurement of BAO at z=2.4 both from the auto-correlation of the LyaF (Sainte Agathe et al. 2019), and from its cross-correlation with quasars (Blomqvist et al. 2019). From the combination of these studies we are able to measure the expansion rate of the Universe 11 billion years ago with a 2% uncertainty.

Starting in 2020, the Dark Energy Spectroscopic Instrument (DESI) will increase this data set by an order of magnitude. DESI will provide an exquisite measurement of the expansion over cosmic time, while at the same time addressing other interesting questions: the sum of the mass of the neutrino species, properties of dark matter particles, tests of general relativity and the shape of the primordial power spectrum of density fluctuations.
### After the Habitable Zone

**Start:** 12:30h

**Speaker:** Prof. Rory Barnes (University of Washington Department of Astronomy, Virtual Planetary Lab )

**Place:** Alberto Lobo Seminar Room (ICE, UAB Campus)

**Start:** 12:30h

**Speaker:** Prof. Rory Barnes (University of Washington Department of Astronomy, Virtual Planetary Lab )

**Place:** Alberto Lobo Seminar Room (ICE, UAB Campus)

The habitable zone (HZ), that region around a star in which the Earth could retain surface water, has served scientists well as they began to idnetify exoplanets that could support liquid water. However, as we move into the era of targeting exoplanets for biosignature detection, the simplifications inherent to the HZ are being exposed. Stellar evolution, internal properties, flares, ocean behavior, tidal effects, galactic perturbations, and orbital oscillations all affect the habitability of exoplanets. As astrobiologists and astronomers begin the first remote sensing campaigns of potential habitable worlds in the next decade, a new paradigm must emerge in which models of planetary system formation and evolution are compared to observational data, both spectral and photometric. This new approach will require a massive and collaborative effort between scientists across a range of disciplines, including leveraging new insights from data scientists to analyze the large and high-dimensional data sets that must be generated and compared. Ultimately the discovery of active biology requires that all possible histories of a planet are simulated and compared to observations to find that only those case that include a biosphere are consistent with data. Developing a framweork to build these formation and evolutionary models is a grand scientific challenge of the 21st century, but the successful discovery of life beyond the Solar System depends on its creation and implementation.
### PBHs-as-CDM scenario and Gravitational Waves

**Start:** 12:00h

**Speaker:** Dr. Misao Sasaki (IPMU, Tokyo, Japan)

**Place:** Alberto Lobo room

**Start:** 12:00h

**Speaker:** Dr. Misao Sasaki (IPMU, Tokyo, Japan)

**Place:** Alberto Lobo room

We argue that primordial black holes (PBHs) with mass of an asteroid can be CDM of the Universe. In this scenario, the associated curvature perturbations will produce secondary gravitational waves with a unique spectral feature, and the amount produced will be large enough to be detected by the future space gravitational wave antenna, LISA.
### Bouncing solutions in modified gravity

**Start:** 12:00h

**Speaker:** Dr. Gauranga Samanta

**Place:** L3-03 workshop room.

**Start:** 12:00h

**Speaker:** Dr. Gauranga Samanta

**Place:** L3-03 workshop room.

In this talk I would like to discuss about the modification of general relativity and why we need the modification. Subsequently, I will discuss about the bouncing solutions in modified gravity. Bouncing problem is one of the fascinating parts of the study of cosmological dynamics in modified gravity, because the big bang singularity could be avoided by a big bounce.The indication of the bouncing universe is: the size of the scale factor contracted to a finite volume.
### Free energy for Dirac comb

**Start:** 12:00h

**Speaker:** M. Bordag (University of Leipzig · Institute of Theoretical Physics)

**Place:** Alberto Lobo Room

**Start:** 12:00h

**Speaker:** M. Bordag (University of Leipzig · Institute of Theoretical Physics)

**Place:** Alberto Lobo Room

The thermodynamic quantities for a non-interacting scalar field in a potential composed of a one-dimensional chain of delta functions are calculated. We start from a system confined to a finite box, whose size is subsequently sent to infinity. First, we consider the representation in terms of real frequencies (or one-particle energies). Then we turn to imaginary frequencies and derive the corresponding Matsubara representation. In the limiting case T~0 we confirm earlier results on the vacuum energy. Additionally we separate the ground state contribution and show that for attractive potentials Bose-Einstein condensation appears.
### What do we want from Baryon Acoustic Oscillations?

**Start:** 12:00h

**Speaker:** Stefano Anselmi (LUTH Observatoire de Paris & Institut d’Astrophysique de Paris)

**Place:** Sala Alberto Lobo (ICE)

**Start:** 12:00h

**Speaker:** Stefano Anselmi (LUTH Observatoire de Paris & Institut d’Astrophysique de Paris)

**Place:** Sala Alberto Lobo (ICE)

Baryon Acoustic Oscillations (BAO) are one of the most useful and used cosmological probes to measure cosmological distances independently of the underlying background cosmology. However, in the current measurements, the inference is done using a theoretical clustering correlation function template where the cosmological and the non-linear damping parameters are kept fixed to fiducial LCDM values. How can we then claim that the measured distances are model-independent and so useful to select cosmological models?

Motivated by this compelling question we introduce a rigorous tool to measure cosmological distances without assuming a specific background cosmology: the “Purely-Geometric-BAO”. I will explain how to practically implement this tool with clustering data. This allows us to quantify the effects of the standard measurements’ assumptions. I will then focus on a new approach to the problem that leverages a novel BAO cosmological standard ruler: the “Linear Point”. Its standard ruler properties allow us to estimate cosmological distances without the need of modeling the poorly-known late-time nonlinear corrections to the linear correlation function. Last but not least, it also provides smaller statistical uncertainties with respect to the correlation function template fit.
### Sitter and Power-law Solutions in Non-local Gauss-Bonnet Gravity

**Start:** 12:00h

**Speaker:** S.Yu. Vernov

**Place:** Alberto Lobo Conference Room S1-01

**Start:** 12:00h

**Speaker:** S.Yu. Vernov

**Place:** Alberto Lobo Conference Room S1-01

The cosmological dynamics of a non-locally corrected gravity theory, involving a power of the inverse d'Alembertian, is investigated. Casting the dynamical equations into local form, the xed points of the models are derived, as well as corresponding de Sitter and power-law solutions. Necessary and sufficient conditions on the model parameters for the existence of de Sitter solutions are obtained. The possible existence of power-law solutions is investigated, and it is proven that models with de Sitter solutions have no power-law solutions. A model is found, which allows describing the matter-dominated phase of the Universe evolution.

07

October 2019

October 2019

The intriguing question, why the present scale of the universe is free from any perceptible footprints of rank-2 antisymmetric tensor fields (generally known as Kalb-Ramond fields), is addressed. A quite natural explanation of this issue is given from the angle of higher-curvature gravity, both in four-…

The intriguing question, why the present scale of the universe is free from any perceptible footprints of rank-2 antisymmetric tensor fields (generally known as Kalb-Ramond fields), is addressed. A quite natural explanation of this issue is given from the angle of higher-curvature gravity, both in four- and in five-dimensional spacetime. The results here obtained reveal that the amplitude of the Kalb-Ramond field may be actually large and playa significant role during the early universe, while the presence of higher-order gravity suppresses this field during the cosmological evolution, so that it eventually becomes negligible in the current universe. Besides the suppression of the Kalb-Ramond field, the extra degree of freedom in F(R) gravity, usually known as scalaron, also turns out to be responsible for inflation. Such F(R) gravity with Kalb-Ramond fields may govern the early universe to undergo an inflationary stage at early times (with the subsequent graceful exit) for a wider range of F(R) gravity than without antisymmetric fields. Furthermore, the models—in four-and five-dimensional spacetimes—are linked to observational constraints, with the conclusion that the corresponding values of the spectral index and tensor-to-scalar ratio closely match the values provided by the Planck survey 2018 data.

07

October 2019

October 2019

I will present some exact cosmological solutions for modified gravity based on a nonlocal operator acting between two factors of the square root of R â€“ 2 Lambda. One of these solutions imitates properties similar to an interplay of the dark matter and the dark energy. For this solution, we computed…

I will present some exact cosmological solutions for modified gravity based on a nonlocal operator acting between two factors of the square root of R â€“ 2 Lambda. One of these solutions imitates properties similar to an interplay of the dark matter and the dark energy. For this solution, we computed some cosmological parameters which are in a good agreement with observations. This talk is based on a recent paper published in Phys. Lett. B.

13

September 2019

September 2019

From 2009 to 2014, the Baryon Oscillation Spectroscopic Survey (BOSS) used the SDSS telescope to obtain spectra of 1.5 million galaxies to get very accurate measurements of the Baryon Acoustic Oscillations (BAO) scale at redshift z ~0.5. At the same time, BOSS observed over 184 000 high redshift…

From 2009 to 2014, the Baryon Oscillation Spectroscopic Survey (BOSS) used the SDSS telescope to obtain spectra of 1.5 million galaxies to get very accurate measurements of the Baryon Acoustic Oscillations (BAO) scale at redshift z ~0.5. At the same time, BOSS observed over 184 000 high redshift quasars (z>2.15) with the goal of detecting the BAO feature in the clustering of the intergalactic medium, using a technique known as the Lyman alpha forest (LyaF).

In this talk I will overview the final results from the LyaF working group in BOSS, and I will present updated results obtained with the extended BOSS survey (eBOSS, 2014-2019). This include the measurement of BAO at z=2.4 both from the auto-correlation of the LyaF (Sainte Agathe et al. 2019), and from its cross-correlation with quasars (Blomqvist et al. 2019). From the combination of these studies we are able to measure the expansion rate of the Universe 11 billion years ago with a 2% uncertainty.

Starting in 2020, the Dark Energy Spectroscopic Instrument (DESI) will increase this data set by an order of magnitude. DESI will provide an exquisite measurement of the expansion over cosmic time, while at the same time addressing other interesting questions: the sum of the mass of the neutrino species, properties of dark matter particles, tests of general relativity and the shape of the primordial power spectrum of density fluctuations.

30

July 2019

July 2019

The habitable zone (HZ), that region around a star in which the Earth could retain surface water, has served scientists well as they began to idnetify exoplanets that could support liquid water. However, as we move into the era of targeting exoplanets for biosignature detection, the simplifications…

The habitable zone (HZ), that region around a star in which the Earth could retain surface water, has served scientists well as they began to idnetify exoplanets that could support liquid water. However, as we move into the era of targeting exoplanets for biosignature detection, the simplifications inherent to the HZ are being exposed. Stellar evolution, internal properties, flares, ocean behavior, tidal effects, galactic perturbations, and orbital oscillations all affect the habitability of exoplanets. As astrobiologists and astronomers begin the first remote sensing campaigns of potential habitable worlds in the next decade, a new paradigm must emerge in which models of planetary system formation and evolution are compared to observational data, both spectral and photometric. This new approach will require a massive and collaborative effort between scientists across a range of disciplines, including leveraging new insights from data scientists to analyze the large and high-dimensional data sets that must be generated and compared. Ultimately the discovery of active biology requires that all possible histories of a planet are simulated and compared to observations to find that only those case that include a biosphere are consistent with data. Developing a framweork to build these formation and evolutionary models is a grand scientific challenge of the 21st century, but the successful discovery of life beyond the Solar System depends on its creation and implementation.

08

July 2019

July 2019

We argue that primordial black holes (PBHs) with mass of an asteroid can be CDM of the Universe. In this scenario, the associated curvature perturbations will produce secondary gravitational waves with a unique spectral feature, and the amount produced will be large enough to be detected by the future…

We argue that primordial black holes (PBHs) with mass of an asteroid can be CDM of the Universe. In this scenario, the associated curvature perturbations will produce secondary gravitational waves with a unique spectral feature, and the amount produced will be large enough to be detected by the future space gravitational wave antenna, LISA.

01

July 2019

July 2019

In this talk I would like to discuss about the modification of general relativity and why we need the modification. Subsequently, I will discuss about the bouncing solutions in modified gravity. Bouncing problem is one of the fascinating parts of the study of cosmological dynamics in modified gravity,…

In this talk I would like to discuss about the modification of general relativity and why we need the modification. Subsequently, I will discuss about the bouncing solutions in modified gravity. Bouncing problem is one of the fascinating parts of the study of cosmological dynamics in modified gravity, because the big bang singularity could be avoided by a big bounce.The indication of the bouncing universe is: the size of the scale factor contracted to a finite volume.

12

March 2019

March 2019

The thermodynamic quantities for a non-interacting scalar field in a potential composed of a one-dimensional chain of delta functions are calculated. We start from a system confined to a finite box, whose size is subsequently sent to infinity. First, we consider the representation in terms of real…

The thermodynamic quantities for a non-interacting scalar field in a potential composed of a one-dimensional chain of delta functions are calculated. We start from a system confined to a finite box, whose size is subsequently sent to infinity. First, we consider the representation in terms of real frequencies (or one-particle energies). Then we turn to imaginary frequencies and derive the corresponding Matsubara representation. In the limiting case T~0 we confirm earlier results on the vacuum energy. Additionally we separate the ground state contribution and show that for attractive potentials Bose-Einstein condensation appears.

21

February 2019

February 2019

Baryon Acoustic Oscillations (BAO) are one of the most useful and used cosmological probes to measure cosmological distances independently of the underlying background cosmology. However, in the current measurements, the inference is done using a theoretical clustering correlation function template where…

Baryon Acoustic Oscillations (BAO) are one of the most useful and used cosmological probes to measure cosmological distances independently of the underlying background cosmology. However, in the current measurements, the inference is done using a theoretical clustering correlation function template where the cosmological and the non-linear damping parameters are kept fixed to fiducial LCDM values. How can we then claim that the measured distances are model-independent and so useful to select cosmological models?

Motivated by this compelling question we introduce a rigorous tool to measure cosmological distances without assuming a specific background cosmology: the “Purely-Geometric-BAO”. I will explain how to practically implement this tool with clustering data. This allows us to quantify the effects of the standard measurements’ assumptions. I will then focus on a new approach to the problem that leverages a novel BAO cosmological standard ruler: the “Linear Point”. Its standard ruler properties allow us to estimate cosmological distances without the need of modeling the poorly-known late-time nonlinear corrections to the linear correlation function. Last but not least, it also provides smaller statistical uncertainties with respect to the correlation function template fit.

20

September 2018

September 2018

The cosmological dynamics of a non-locally corrected gravity theory, involving a power of the inverse d'Alembertian, is investigated. Casting the dynamical equations into local form, the xed points of the models are derived, as well as corresponding de Sitter and power-law solutions. Necessary…

The cosmological dynamics of a non-locally corrected gravity theory, involving a power of the inverse d'Alembertian, is investigated. Casting the dynamical equations into local form, the xed points of the models are derived, as well as corresponding de Sitter and power-law solutions. Necessary and sufficient conditions on the model parameters for the existence of de Sitter solutions are obtained. The possible existence of power-law solutions is investigated, and it is proven that models with de Sitter solutions have no power-law solutions. A model is found, which allows describing the matter-dominated phase of the Universe evolution.

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