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We investigate the potential of the warped-extradimension framework as an explanation for the recently observed stochastic gravitational background at nHz frequencies in pulsar timing arrays (PTA). Our analysis reveals that the PTA data can be effectively accommodated by a first-order phase transition triggered by a radion at the MeV-GeV scale feebly coupled to the Standard Model. Remarkably, this outcome remains robust irrespective of the specific details of the warped extradimension embedding, providing a foundation for future investigations aiming to develop concrete extradimension descriptions of Nature. We also demonstrate that many existing embeddings are not viable, as their radion and graviton phenomenology clash with a MeV-GeV scale radion. As a possible way-out, we sketch a promising solution involving multiple branes, wherein the light radion, graviton, and ensuing light resonances remain consistent with collider bounds and gravity tests., 14 pages, 3 figures

We use the latest constraints on the population of stellar origin binary black holes (SOBBH) from LIGO/Virgo/KAGRA (LVK) observations, to estimate the stochastic gravitational wave background (SGWB) they generate in the frequency band of LISA. We account for the faint and distant binaries, which contribute the most to the SGWB, by extending the merger rate at high redshift assuming it tracks the star formation rate. We adopt different methods to compute the SGWB signal: an analytical evaluation, Monte Carlo sums over SOBBH population realisations, and a method that accounts for the role of the detector by simulating LISA data and iteratively removing resolvable signals until only the confusion noise is left, allowing for the extraction of both the expected SGWB and the number of resolvable SOBBHs. Since the latter are few for SNR thresholds larger than five, we confirm that the spectral shape of the SGWB in the LISA band follows the analytical prediction of a power law. We infer the probability distribution of the SGWB amplitude from the LVK GWTC-3 posterior of the binary population model; its interquartile range of $h^2\Omega_\mathrm{GW}(f=3\times10^{-3}\,\mathrm{Hz}) \in [5.65,\,11.5]\times10^{-13}$ is in agreement with most previous estimates. We perform a MC analysis to assess LISA's capability to detect and characterise this signal. Accounting for both the instrumental noise and the galactic binaries foreground, with four years of data, LISA will be able to detect the SOBBH SGWB with percent accuracy, narrowing down the uncertainty on the amplitude by one order of magnitude with respect to the range of possible amplitudes inferred from the population model. A measurement of this signal by LISA will help to break the degeneracy among some of the population parameters, and provide interesting constraints, in particular on the redshift evolution of the SOBBH merger rate., Comment: 39 pages, 15 figures. Prepared for submission to JCAP

et al., The science objectives of the LISA mission have been defined under the implicit assumption of a 4-years continuous data stream. Based on the performance of LISA Pathfinder, it is now expected that LISA will have a duty cycle of ≈0.75 , which would reduce the effective span of usable data to 3 years. This paper reports the results of a study by the LISA Science Group, which was charged with assessing the additional science return of increasing the mission lifetime. We explore various observational scenarios to assess the impact of mission duration on the main science objectives of the mission. We find that the science investigations most affected by mission duration concern the search for seed black holes at cosmic dawn, as well as the study of stellar-origin black holes and of their formation channels via multi-band and multi-messenger observations. We conclude that an extension to 6 years of mission operations is recommended., C.P.L. Berry is supported by the CIERA Board of Visitors Professorship. E. Berti is supported by NSF Grants No. PHY-1912550 and AST-2006538, NASA ATP Grants No. 17-ATP17-0225 and 19-ATP19-0051, NSF-XSEDE Grant No. PHY-090003, and NSF Grant PHY-20043. D. Blas acknowledges support from the Fundación Jesus Serra and the Instituto de Astrofísica de Canarias under the Visiting Researcher Programme 2021 agreed between both institutions. T. Bogdanović acknowledges the support by the National Aeronautics and Space Administration (NASA) under award No. 80NSSC19K0319 and by the National Science Foundation (NSF) under Award No. 1908042. V. Cardoso acknowledges financial support provided under the European Union’s H2020 ERC Consolidator Grant “Matter and strong-field gravity: New frontiers in Einstein’s theory” Grant Agreement No. MaGRaTh–646597. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 101007855. We thank FCT for financial support through Projects No. UIDB/00099/2020 and through grants PTDC/MAT-APL/30043/2017 and PTDC/FIS-AST/7002/2020. H.-Y. Chen is supported by NASA through NASA Hubble Fellowship Grants No. HST-HF2-51452.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. Z. Haiman acknowledges support by NASA Grant NNX15AB19G and NSF Grants AST-2006176 and AST-1715661. G. Nardini is partly supported by the ROMFORSK Grant Project. No. 302640 “Gravitational Wave Signals From Early Universe Phase Transitions”. P. Pani acknowledges financial support provided under the European Union’s H2020 ERC, Starting Grant Agreement No. DarkGRA–757480. He also acknowledges support under the MIUR PRIN and FARE programmes (GW-NEXT, CUP: B84I20000100001), and by the Amaldi Research Center funded by the MIUR program “Dipartimento di Eccellenza” (CUP: B81I18001170001). A. Sesana acknowledges financial support provided under the European Union’s H2020 ERC Consolidator Grant “Binary Massive Black Hole Astrophysics” (B Massive, Grant Agreement: 818691). K. Yagi acknowledges support from NSF Grant PHY-1806776, NASA Grant 80NSSC20K0523, a Sloan Foundation Research Fellowship and the Owens Family Foundation. D. J. Weir was supported by a Science and Technology Facilities Council Ernest Rutherford Fellowship, Grant no. ST/R003904/1, and by the Academy of Finland, Grants 324882 and 328958. A. Zimmerman is supported by NSF Grant No. PHY-1912578. The authors would like to acknowledge networking support by the GWverse COST Action CA16104, “Black holes, gravitational waves and fundamental physics.” The Flatiron Institute is supported by the Simons Foundation. This research has made use of data, software and web tools obtained from the Gravitational Wave Open Science Center (www.gw-openscience.org/), a service of LIGO Laboratory, the LIGO Scientific Collaboration and the Virgo Collaboration. LIGO Laboratory and Advanced LIGO are funded by the United States National Science Foundation (NSF) as well as the Science and Technology Facilities Council (STFC) of the United Kingdom, the Max-Planck-Society (MPS), and the State of Niedersachsen/Germany for support of the construction of Advanced LIGO and construction and operation of the GEO600 detector. Additional support for Advanced LIGO was provided by the Australian Research Council. Virgo is funded, through the European Gravitational Observatory (EGO), by the French Centre National de Recherche Scientifique (CNRS), the Italian Istituto Nazionale di Fisica Nucleare (INFN) and the Dutch Nikhef, with contributions by institutions from Belgium, Germany, Greece, Hungary, Ireland, Japan, Monaco, Poland, Portugal, Spain.

Following the selection of The Gravitational Universe by ESA, and the successful flight of LISA Pathfinder, the LISA Consortium now proposes a 4 year mission in response to ESA's call for missions for L3. The observatory will be based on three arms with six active laser links, between three identical spacecraft in a triangular formation separated by 2.5 million km. LISA is an all-sky monitor and will offer a wide view of a dynamic cosmos using Gravitational Waves as new and unique messengers to unveil The Gravitational Universe. It provides the closest ever view of the infant Universe at TeV energy scales, has known sources in the form of verification binaries in the Milky Way, and can probe the entire Universe, from its smallest scales near the horizons of black holes, all the way to cosmological scales. The LISA mission will scan the entire sky as it follows behind the Earth in its orbit, obtaining both polarisations of the Gravitational Waves simultaneously, and will measure source parameters with astrophysically relevant sensitivity in a band from below $10^{-4}\,$Hz to above $10^{-1}\,$Hz., Submitted to ESA on January 13th in response to the call for missions for the L3 slot in the Cosmic Vision Programme

© 2019 IOP Publishing Ltd. The grand challenges of contemporary fundamental physics-dark matter, dark energy, vacuum energy, inflation and early universe cosmology, singularities and the hierarchy problem-all involve gravity as a key component. And of all gravitational phenomena, black holes stand out in their elegant simplicity, while harbouring some of the most remarkable predictions of General Relativity: event horizons, singularities and ergoregions. The hitherto invisible landscape of the gravitational Universe is being unveiled before our eyes: the historical direct detection of gravitational waves by the LIGO-Virgo collaboration marks the dawn of a new era of scientific exploration. Gravitational-wave astronomy will allow us to test models of black hole formation, growth and evolution, as well as models of gravitational-wave generation and propagation. It will provide evidence for event horizons and ergoregions, test the theory of General Relativity itself, and may reveal the existence of new fundamental fields. The synthesis of these results has the potential to radically reshape our understanding of the cosmos and of the laws of Nature. The purpose of this work is to present a concise, yet comprehensive overview of the state of the art in the relevant fields of research, summarize important open problems, and lay out a roadmap for future progress. This write-up is an initiative taken within the framework of the European Action on 'Black holes, Gravitational waves and Fundamental Physics'.

Following the selection of The Gravitational Universe by ESA, and the successful flight of LISA Pathfinder, the LISA Consortium now proposes a 4 year mission in response to ESA's call for missions for L3. The observatory will be based on three arms with six active laser links, between three identical spacecraft in a triangular formation separated by 2.5 million km. LISA is an all-sky monitor and will offer a wide view of a dynamic cosmos using Gravitational Waves as new and unique messengers to unveil The Gravitational Universe. It provides the closest ever view of the infant Universe at TeV energy scales, has known sources in the form of verification binaries in the Milky Way, and can probe the entire Universe, from its smallest scales near the horizons of black holes, all the way to cosmological scales. The LISA mission will scan the entire sky as it follows behind the Earth in its orbit, obtaining both polarisations of the Gravitational Waves simultaneously, and will measure source parameters with astrophysically relevant sensitivity in a band from below $10^{-4}\,$Hz to above $10^{-1}\,$Hz.

If the Standard Model (SM) is an effective theory, as currently believed, it is valid up to some energy scale $\Lambda$ to which the Higgs vacuum expectation value is sensitive throughout radiative quadratic terms. These can destabilize the electroweak vacuum and generate the SM hierarchy problem. For a given perturbative Ultraviolet (UV) completion, the SM cutoff can be computed in terms of physical masses. If the UV mass spectrum involves several scales the cutoff is not unique and each sector has its own UV cutoff $\Lambda_i$. We have performed this calculation assuming the Minimal Supersymmetric Standard Model (MSSM) is the SM UV completion. As a result, from the SM point of view, the quadratic correction to the Higgs mass is equivalent to finite threshold contributions. For the measured values of the top quark and Higgs masses, and depending on the values of the different cutoffs $\Lambda_i$, these contributions can cancel even at TeV scales, unlike the case of a unique cutoff where the cancellation occurs at Planckian energies. Gauginos heavier than squarks tend to be favored. From the UV MSSM point of view, the quadratic sensitivity is incorporated into the matching conditions and for instance it provides an extra constraint on the Focus Point solution to the little hierarchy problem in the MSSM.

I denne artikkelen har jeg vist at de empiriske resultatene til Johannes Kepler, beskrivende modeller av vårt solsystem basert på observasjoner gjort av Tycho Brahe, kan utledes fra Newtons bevegelsessetniger. Disse utledningene, som er basert på matematiske modeller, åpner for ny innsikt som var skjult av unøyaktighetene i Brahe's observasjoner. Jeg har også vist at numeriske løsninger generert i Wolfram Mathematica har tilstrekkelig nøyaktighet til å modelere planetenes baner i minst en periode. In this paper I have shown that the empirical results of Johannes Kepler, descriptive models of our solar system based on the observational data of Tycho Brahe, can be derived from the laws of motion later postulated by Newton. This derivation which is based on mathematical models, allows for newer insights which were obscured by the inaccuracies in Brahe's data. I have also found that the numerical solutions of Wolfram Mathematica, while producing some errors, are accurate enough to model the orbits of planets for up to at least the time of their orbital period.

The grand challenges of contemporary fundamental physics dark matter, dark energy, vacuum energy, inflation and early universe cosmology, singularities and the hierarchy problem all involve gravity as a key component. And of all gravitational phenomena, black holes stand out in their elegant simplicity, while harbouring some of the most remarkable predictions of General Relativity: event horizons, singularities and ergoregions.The hitherto invisible landscape of the gravitational Universe is being unveiled before our eyes: the historical direct detection of gravitational waves by the LIGO-Virgo collaboration marks the dawn of a new era of scientific exploration. Gravitational-wave astronomy will allow us to test models of black hole formation, growth and evolution, as well as models of gravitational-wave generation and propagation. It will provide evidence for event horizons and ergoregions, test the theory of General Relativity itself, and may reveal the existence of new fundamental fields. The synthesis of these results has the potential to radically reshape our understanding of the cosmos and of the laws of Nature.The purpose of this work is to present a concise, yet comprehensive overview of the state of the art in the relevant fields of research, summarize important open problems, and lay out a roadmap for future progress., European Union (EU); European Cooperation in Science and Technology (COST); Polish National Science Center (NCN); Carl Tryggers Foundation; Science & Technology Facilities Council (STFC); European Union's H2020 ERC Consolidator Grant 'Matter and strong-field gravity: New frontiers in Einstein's theory'; European Research Council (ERC); Horizon 2020; Science & Technology Facilities Council (STFC; Ministry of Education and Science of the Republic of Serbia; Foundation for Polish Science; Austrian Science Fund (FWF); Polish National Center of Science (NCN); European Research Council (ERC); Hungarian National Research, Development, and Innovation Office; Swiss National Science Foundation (SNSF); European Union's H2020 ERC; H2020-MSCA-RISE-2015 Grant; National Science Foundation (NSF); PRACE; Simons Foundation; Ministry of Economy, Industry and Competitiveness of Spain; Slovenian Research Agency - Slovenia; EU H2020 under ERC; Spanish MINECO; Generalitat Valenciana; NASA by the Chandra X-ray Center; National Aeronautics & Space Administration (NASA); Scientific and Technological Research Council of Turkey (TÜBİTAK); H2020-MSCA-RISE-2017 Grant; Scientific and Technological Research Council of Turkey (TÜBİTAK); National Science Centre of Poland - European Union; Deutscher Akademischer Austausch Dienst (DAAD); GWAVES of ARIS-GRNET(Athens); Royal Society of London; Research Grant; Scientific and Technological Research Council of Turkey (TÜBİTAK)

This thesis consists of three separate research papers, and an introductory overview concentrating on the physics relevant for these subjects. In the first paper we use classical, real-time simulations to study gravitational wave production in the early Universe. The second paper focuses on extended Technicolor corrections to the Higgs mass. The third paper uses lattice gauge field theory to study the properties of a strongly interacting SU(2) gauge model with fermions in the fundamental representation. Many cosmological models suggest that an inflatory epoch took place in the early Universe, and it was followed by a "reheating" phase. These events might have emitted gravitational waves, which could be detectable today as a primordial gravitational wave background. Using large-scale numerical simulations we compute the gravitational wave spectrum from a tachyonic preheating transition of a Standard Model like SU(2)-like Higgs system. Comparing non-Abelian and Abelian models to their scalar-only counterparts, we find that adding the non-Abelian gauge field to a scalar-only theory reduces and the Abelian gauge field increases the gravitational wave production, but unfortunately none of these models fall in the detection region of LISA. All known elementary particles and three of the four fundamental forces of nature are described by the Standard Model (SM). However, it leaves some phenomena unexplained, which leads us believe that the SM must be extended in some way. We focus on Technicolor (TC) theory that generates the masses of the W and Z bosons through the dynamics of the new gauge interactions. Extending the gauge dynamics of TC, effectively represented by four fermion interactions, we can generate the masses of SM fermions, but instead of the 125 GeV scalar, TC typically predicts a scalar state of the order of 1 TeV. We show that by systematically treating these four-fermion interactions, the mass of the scalar resonance can be greatly reduced while remaining in agreement with the experimental constraints of the oblique corrections. Building a successful extended Technicolor (ETC) model has proven to be difficult, as it is challenged by experimental constraints on flavor-changing neutral currents and precision electroweak measurements. Walking TC models suggest that the gauge couplings must evolve very slowly, i.e walk instead of run, over a certain range of energy scales. Walking behaviour exhibits nearly conformal behavior that is caused by an infrared fixed point (IRFP), but a theory with an IRFP must be studied by lattice field simulations due to its non-perturbative effects. We compute the mass spectrum of SU(2) gauge theory with two, four and six massless Dirac fermions in the fundamental representation of the gauge group. We observe that $N_f=$ 2 and 4 behave with the usual pattern of chiral symmetry breaking, whereas our results for $N_f=6$ indicate the existence of an IRFP. Suurin osa hyvin varhaisen maailmankaikkeuden vaiheista on edelleen selvittämättä. Yksi mahdollinen tapa tutkia universumin alun tapahtumia on mitata gravitaatioaaltoja. Gravitaatioaaltoja syntyy suurten mullistusten yhteydessä, kuten kahden massiivisen kappaleen törmäyksessä. Erilaisten mallien tuottamia gravitaatioaaltoja voidaan laskea teoreettisesti, ja verrata niitä havaintoihin. Gravitaatioaaltojen mittaaminen on kuitenkin vaikeaa, mutta suuri etappi saavutettiin vuonna 2016, kun ilmoitettiin, että yhdysvaltalaisella LIGO-laitteistolla oltiin saatu suora havainto gravitaatioaalloista. Lisäksi suunnitteilla oleva LISA-satelliitti voisi havaita myös kosmologista alkuperää olevia gravitaatioaaltoja. Tämän väitöskirjan ensimmäisessä osassa tutkimme yhtä varhaisen maailmankaikkeuden mallia. Tietokonesimulaatioiden avulla laskemme sen ennustamien gravitaatioaaltojen taajuuden ja voimakkuuden, joita vertaamme tulevien koelaitteiden mittausrajoihin. Hiukkasfysiikan standardimalli kuvaa kvanttikenttäteorian avulla kolme perusvuorovaikutusta sekä tunnetut alkeishiukkaset. 1970-luvulla luotu teoria on osoittautunut erittäin menestykselliseksi, ja vuonna 2012 ilmoitettu Higgsin bosonin löytyminen varmisti teorian pätevyyden hiukkasfysiikan perustana. Standardimallia on kuitenkin laajennettava, sillä nykyisellään se ei onnistu selittämään kaikkia tunnettuja ilmiöitä, eikä mallissa ole esimerkiksi yhtään mahdollista pimeän aineen hiukkasta. Tässä väitöskirjassa keskitymme yhteen mahdolliseen standardimallin laajennukseen, tekniväriteoriaan. Tekniväriteorioissa Higgsin hiukkanen koostuu pienemmistä hiukkasista, teknikvarkeista, samankaltaisesti kuin esimerkiksi hiukkasfysiikan standardimallissa protoni ja neutroni koostuvat kvarkeista. Suora analogia kvarkkien ja teknikvarkkien välillä kuitenkin ontuu. Varhaiset teknivärimallit ennustivat noin kymmenen kertaa suuremman Higgsin massan kuin mitä CERNissä tehdyt mittaukset osoittivat. Väitöskirjan toisessa osassa osoitamme, että tietyin muutoksin tutkittu teknivärimalli on sopusoinnussa mitatun Higgsin massan kanssa. Kolmannessa osassa tutkimme hilasimulaatioilla, kuinka monta erilaista teknikvarkkia täytyisi tietynlaisessa mallissa olla, jotta malli olisi sopusoinnussa kokeellisten tulosten kanssa.