Browsing by Subject "inflation"

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  • Enckell, Vera-Maria; Enqvist, Kari; Räsänen, Syksy; Wahlman, Lumi-Pyry (2019)
    We study scalar field inflation in F(R) gravity in the Palatini formulation of general relativity. Unlike in the metric formulation, in the Palatini formulation F(R) gravity does not introduce new degrees of freedom. However, it changes the relations between existing degrees of freedom, including the inflaton and spacetime curvature. Considering the case F(R) = R + alpha R-2, we find that the R-2 term decreases the height of the effective inflaton potential. By adjusting the value of a, this mechanism can be used to suppress the tensor-to-scalar ratio r without limit in any scalar field model of inflation without affecting the spectrum of scalar perturbations.
  • Lehtiniemi, Tuukka (2008)
    In this thesis, I examine the economic systems revolving around production and exchange of virtual property. From my viewpoint, the central forms of virtual property include e.g. virtual items in community sites, and virtual goods and characters in online games. Production of virtual property often requires significant time inputs from the users, and the users also trade it for real money. I treat these economic systems, called virtual economies, as sufficiently separate economies whose macroeconomic properties can be discussed. Particularly, I focus on the question “Can meaningful macroeconomic indicators be computed for a virtual economy?” The macroeconomic indicators that are investigated in this study are aggregate production and inflation. My approach is to identify relevant principles using which these indicators are computed for national economies, and then transfer the same principles to a virtual economy. The developed aggregate production measure, called Gross User Product (GUP), is defined based on the principles underlying the System of National Accounts (SNA). GUP measures the aggregate economic activities of the users of a virtual economy. The central feature of GUP is that it makes a distinction between production by the users and production by the service they use. The possibility to log potentially all transactions in a virtual economy allows for flexible choice of an inflation measure. Measuring inflation for a virtual economy is, in this sense, easier than for e.g. a national economy. The employed inflation measure is a chained Fischer index, which is computed based on market transaction data of virtual final goods. Both macroeconomic indicators are computed for the virtual economy of EVE Online. The economy of EVE Online consists of production and exchange activities of about 200,000 users, all of who potentially interact with each other. Transaction and production data from the logs of EVE Online is employed in the computations. The previously published research on macroeconomic indicators for a virtual economy has focused on using data collected from real-money trading markets external to the virtual economy. This study shows that virtual economies can be regarded as separate economic systems, and that comprehensive macroeconomic indicators can be computed for them. The employed tools of economics transfer well to the analysis of a virtual economy. The results can be used for e.g. tracking the state of a virtual economy and macroeconomic modeling.
  • Piippo, Iida (Helsingin yliopisto, 2019)
    Housing prices in many countries have experienced large run-ups and downturns which indicates that the housing market is not working efficiently. Understanding the factors affecting the house price movement is important to be able to prevent radical price changes and maintain economic stability. One cause for the inefficiency in the housing market has been proposed to be the money illusion. Money illusionary agents make inflation adjustment errors by discounting the future real payoffs with nominal rather than real interest rate. This irrational behavior of agents has been shown to cause pricing errors especially at the times when inflation is exceptionally high or low. The money illusion hypothesis has widely been studied in the context of the financial and housing market. This thesis contributes to the existing literature by studying if there is evidence of the money illusion in the Finnish housing market. Many of the studies have focused on the major economic markets like the UK and the US, so there are not many studies from the perspective of a national market with different institutional setting and market features. The empirical framework is based on the decomposition of the price-rent ratio. The intention is to differentiate the fundamentals of the housing market to study how different unobservable factors affect housing. Housing is considered as a dividend paying asset as in the financial market approach. The study shows that there is a link between inflation and price-rent ratio. Inflation can affect prices through the rational component, risk premia or pricing errors. Money illusion suggests that inflation affect prices through the pricing error. In the model, the agents are allowed to have subjective expectations in order to be able to obtain the pricing error which is the difference between the rational agents objective expectations and irrational agents subjective expectations. The results from the Finnish housing market differ from other studies documenting strong evidence in favor of the money illusion. There is no strong evidence to the hypothesis that inflation and nominal interest rate would explain the movements in the pricing error. However, the rational component and the risk premia of the housing are highly correlated with inflation and nominal interest rates. The results of this study show more support for the rational channels than to the irrational channels for explaining the detected link between housing prices and inflation. The study also shows that part of the correlation between inflation and price-rent ratio can be explained by business cycle fluctuations. Thus, the study does not find strong evidence of money illusion having an effect on the Finnish housing market.
  • Markkanen, Tommi; Nurmi, Sami; Räsänen, Syksy; Vennin, Vincent (2017)
    We consider inflationary magnetogenesis where the conformal symmetry is broken by the term f(2)(phi)F alpha,beta F alpha,beta. We assume that the magnetic field power spectrum today between 0.1 and 10(4) Mpc is a power law, with upper and lower limits from observation. This fixes f to be close to a power law in conformal time in the window during inflation when the modes observed today are generated. In contrast to previous work, we do not make any assumptions about the form of f outside these scales. We cover all possible reheating histories, described by an average equation of state 1/3 <w <1. Requiring that strong coupling and large back reaction are avoided both at the background and perturbative level, we find the bound delta(B0) <5 x 10(-15) (r/0.07)(1/2) KG for the magnetic field generated by inflation, where r is the tensor -to scalar ratio and kappa is a constant related to the form of f. This estimate has an uncertainty of one order of magnitude related to our approximations. The parameter kappa is <100, and values greater than or similar to 1 require a highly fine-tuned form of f; typical values are orders of magnitude smaller.
  • Enckell, Vera-Maria; Enqvist, Kari; Nurmi, Sami (2016)
    We investigate the dependency of Higgs inflation on the non-renormalisable matching between the low energy Standard Model limit and the inflationary regime at high energies. We show that for the top mass range m(t) greater than or similar to 171.8 GeV the scenario robustly predicts the spectral index n(s) similar or equal to 0.97 and the tensor-to-scalar ratio r similar or equal to 0.003. The matching is however non-trivial, even the best-fit values m(h) = 125.09 GeV and m(t) = 173.21 GeV require a jump delta lambda similar to 0.01 in the Higgs coupling below the inflationary scale. For m(t) less than or similar to 171.8 GeV, the matching may generate a feature in the inflationary potential. In this case the predicted values of n(s) and r vary but the model is still falsifiable. For example, a detection of negative running of spectral index at level alpha(s) less than or similar to -0.01 would rule out Higgs inflation.
  • Ade, P. A. R.; Aghanim, N.; Armitage-Caplan, C.; Arnaud, M.; Ashdown, M.; Atrio-Barandela, F.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Bartlett, J. G.; Battaner, E.; Benabed, K.; Benoit, A.; Benoit-Levy, A.; Bernard, J. -P.; Bersanelli, M.; Bielewicz, P.; Bobin, J.; Bock, J. J.; Bonaldi, A.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Bridges, M.; Bucher, M.; Burigana, C.; Butler, R. C.; Calabrese, E.; Cappellini, B.; Cardoso, J. -F.; Catalano, A.; Challinor, A.; Chamballu, A.; Chary, R. -R.; Chen, X.; Chiang, H. C.; Chiang, L. -Y; Christensen, P. R.; Church, S.; Clements, D. L.; Colombi, S.; Colombo, L. P. L.; Couchot, F.; Coulais, A.; Crill, B. P.; Curto, A.; Cuttaia, F.; Danese, L.; Davies, R. D.; Davis, R. J.; de Bernardis, P.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Delouis, J. -M.; Desert, F. -X.; Dickinson, C.; Diego, J. M.; Dolag, K.; Dole, H.; Donzelli, S.; Dore, O.; Douspis, M.; Dunkley, J.; Dupac, X.; Efstathiou, G.; Elsner, F.; Ensslin, T. A.; Eriksen, H. K.; Finelli, F.; Forni, O.; Frailis, M.; Fraisse, A. A.; Franceschi, E.; Gaier, T. C.; Galeotta, S.; Galli, S.; Ganga, K.; Giard, M.; Giardino, G.; Giraud-Heraud, Y.; Gjerlow, E.; Gonzalez-Nuevo, J.; Gorski, K. M.; Gratton, S.; Gregorio, A.; Gruppuso, A.; Gudmundsson, J. E.; Haissinski, J.; Hamann, J.; Hansen, F. K.; Hanson, D.; Harrison, D.; Henrot-Versille, S.; Hernandez-Monteagudo, C.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Holmes, W. A.; Hornstrup, A.; Hou, Z.; Hovest, W.; Huffenberger, K. M.; Jaffe, A. H.; Jaffe, T. R.; Jewell, J.; Jones, W. C.; Juvela, M.; Keihanen, E.; Keskitalo, R.; Kisner, T. S.; Kneissl, R.; Knoche, J.; Knox, L.; Kunz, M.; Kurki-Suonio, H.; Lagache, G.; Lahteenmaki, A.; Lamarre, J. -M.; Lasenby, A.; Lattanzi, M.; Laureijs, R. J.; Lawrence, C. R.; Leach, S.; Leahy, J. P.; Leonardi, R.; Leon-Tavares, J.; Lesgourgues, J.; Lewis, A.; Liguori, M.; Lilje, P. B.; Linden-Vornle, M.; Lopez-Caniego, M.; Lubin, P. M.; Macias-Perez, J. F.; Maffei, B.; Maino, D.; Mandolesi, N.; Maris, M.; Marshall, D. J.; Martin, P. G.; Martinez-Gonzalez, E.; Masi, S.; Massardi, M.; Matarrese, S.; Matthai, F.; Mazzotta, P.; Meinhold, P. R.; Melchiorri, A.; Melin, J. -B.; Mendes, L.; Menegoni, E.; Mennella, A.; Migliaccio, M.; Millea, M.; Mitra, S.; Miville-Deschenes, M. -A.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Moss, A.; Munshi, D.; Murphy, J. A.; Naselsky, P.; Nati, F.; Natoli, P.; Netterfield, C. B.; Norgaard-Nielsen, H. U.; Noviello, F.; Novikov, D.; Novikov, I.; O'Dwyer, I. J.; Osborne, S.; Oxborrow, C. A.; Paci, F.; Pagano, L.; Pajot, F.; Paladini, R.; Paoletti, D.; Partridge, B.; Pasian, F.; Patanchon, G.; Pearson, D.; Pearson, T. J.; Peiris, H. V.; Perdereau, O.; Perotto, L.; Perrotta, F.; Pettorino, V.; Piacentini, F.; Piat, M.; Pierpaoli, E.; Pietrobon, D.; Plaszczynski, S.; Platania, P.; Pointecouteau, E.; Polenta, G.; Ponthieu, N.; Popa, L.; Poutanen, T.; Pratt, G. W.; Prezeau, G.; Prunet, S.; Puget, J. -L.; Rachen, J. P.; Reach, W. T.; Rebolo, R.; Reinecke, M.; Remazeilles, M.; Renault, C.; Ricciardi, S.; Riller, T.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Roudier, G.; Rowan-Robinson, M.; Rubino-Martin, J. A.; Rusholme, B.; Sandri, M.; Santos, D.; Savelainen, M.; Savini, G.; Scott, D.; Seiffert, M. D.; Shellard, E. P. S.; Spencer, L. D.; Starck, J. -L.; Stolyarov, V.; Stompor, R.; Sudiwala, R.; Sunyaev, R.; Sureau, F.; Sutton, D.; Suur-Uski, A. -S.; Sygnet, J. -F.; Tauber, J. A.; Tavagnacco, D.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tristram, M.; Tucci, M.; Tuovinen, J.; Tuerler, M.; Umana, G.; Valenziano, L.; Valiviita, J.; Van Tent, B.; Vielva, P.; Villa, F.; Vittorio, N.; Wade, A.; Wandelt, B. D.; Wehus, I. K.; White, M.; White, S. D. M.; Wilkinson, A.; Yvon, D.; Zacchei, A.; Zonca, A. (2014)
  • Ade, P. A. R.; Aghanim, N.; Armitage-Caplan, C.; Arnaud, M.; Ashdown, M.; Atrio-Barandela, F.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Bartlett, J. G.; Bartolo, N.; Battaner, E.; Benabed, K.; Benoit, A.; Benoit-Levy, A.; Bernard, J.-P.; Bersanelli, M.; Bielewicz, P.; Bobin, J.; Bock, J. J.; Bonaldi, A.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Bridges, M.; Bucher, M.; Burigana, C.; Butler, R. C.; Calabrese, E.; Cardoso, J.-F.; Catalano, A.; Challinor, A.; Chamballu, A.; Chiang, H. C.; Chiang, L.-Y.; Christensen, P. R.; Church, S.; Clements, D. L.; Colombi, S.; Colombo, L. P. L.; Juvela, M.; Keihänen, Elina; Keskitalo, R.; Kurki-Suonio, H.; Poutanen, T.; Savelainen, M.; Suur-Uski, A.-S.; Tuovinen, J.; Valiviita, J. (2014)
    We analyse the implications of the Planck data for cosmic inflation. The Planck nominal mission temperature anisotropy measurements, combined with the WMAP large-angle polarization, constrain the scalar spectral index to be n(s) = 0.9603 +/- 0:0073, ruling out exact scale invariance at over 5 sigma Planck establishes an upper bound on the tensor-to-scalar ratio of r <0.11 (95% CL). The Planck data thus shrink the space of allowed standard inflationary models preferring potentials with V '' <0. Exponential potential models, the simplest hybrid inflationary models, and monomial potential models of degree n >= 2 do not provide a good fit to the data. Planck does not find statistically significant running of the scalar spectral index, obtaining dn(s)/dln k = -0.0134 +/- 0.0090. We verify these conclusions through a numerical analysis, which makes no slowroll approximation, and carry out a Bayesian parameter estimation and model-selection analysis for a number of inflationary models including monomial, natural, and hilltop potentials. For each model, we present the Planck constraints on the parameters of the potential and explore several possibilities for the post-inflationary entropy generation epoch, thus obtaining nontrivial data-driven constraints. We also present a direct reconstruction of the observable range of the inflaton potential. Unless a quartic term is allowed in the potential, we find results consistent with second-order slow-roll predictions. We also investigate whether the primordial power spectrum contains any features. We find that models with a parameterized oscillatory feature improve the fit by delta 2 10; however, Bayesian evidence does not prefer these models. We constrain several single-field inflation models with generalized Lagrangians by combining power spectrum data with Planck bounds on fNL. Planck constrains with unprecedented accuracy the amplitude and possible correlation (with the adiabatic mode) of non-decaying isocurvature fluctuations. The fractional primordial contributions of cold dark matter (CDM) isocurvature modes of the types expected in the curvaton and axion scenarios have upper bounds of 0.25% and 3.9% (95% CL), respectively. In models with arbitrarily correlated CDM or neutrino isocurvature modes, an anticorrelated isocurvature component can improve the 2 by approximately 4 as a result of slightly lowering the theoretical prediction for the 40 multipoles relative to the higher multipoles. Nonetheless, the data are consistent with adiabatic initial conditions.
  • Ade, P. A. R.; Aghanim, N.; Armitage-Caplan, C.; Arnaud, M.; Ashdown, M.; Atrio-Barandela, F.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Bartlett, J. G.; Bartolo, N.; Battaner, E.; Benabed, K.; Benoit, A.; Benoit-Levy, A.; Bernard, J. -P.; Bersanelli, M.; Bielewicz, P.; Bobin, J.; Bock, J. J.; Bonaldi, A.; Bonavera, L.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Bridges, M.; Bucher, M.; Burigana, C.; Butler, R. C.; Cardoso, J. -F.; Catalano, A.; Challinor, A.; Chamballu, A.; Chiang, H. C.; Chiang, L. -Y; Christensen, P. R.; Church, S.; Clements, D. L.; Colombi, S.; Colombo, L. P. L.; Couchot, F.; Juvela, M.; Keihanen, E.; Keskitalo, R.; Kurki-Suonio, H.; Poutanen, T.; Suur-Uski, A. -S.; Tuovinen, J.; Valiviita, J. (2014)
  • Planck Collaboration; Akrami, Y.; Keihanen, E.; Kiiveri, K.; Kurki-Suonio, H.; Lindholm, V.; Savelainen, M.; Suur-Uski, A. -S.; Valiviita, J. (2020)
    We analyse the Planck full-mission cosmic microwave background (CMB) temperature and E-mode polarization maps to obtain constraints on primordial non-Gaussianity (NG). We compare estimates obtained from separable template-fitting, binned, and optimal modal bispectrum estimators, finding consistent values for the local, equilateral, and orthogonal bispectrum amplitudes. Our combined temperature and polarization analysis produces the following final results: fNLlocal = −0.9 ± 5.1; fNLequil = −26 ± 47; and fNLortho = −38 ± 24 (68% CL, statistical). These results include low-multipole (4 ≤ ℓ <  40) polarization data that are not included in our previous analysis. The results also pass an extensive battery of tests (with additional tests regarding foreground residuals compared to 2015), and they are stable with respect to our 2015 measurements (with small fluctuations, at the level of a fraction of a standard deviation, which is consistent with changes in data processing). Polarization-only bispectra display a significant improvement in robustness; they can now be used independently to set primordial NG constraints with a sensitivity comparable to WMAP temperature-based results and they give excellent agreement. In addition to the analysis of the standard local, equilateral, and orthogonal bispectrum shapes, we consider a large number of additional cases, such as scale-dependent feature and resonance bispectra, isocurvature primordial NG, and parity-breaking models, where we also place tight constraints but do not detect any signal. The non-primordial lensing bispectrum is, however, detected with an improved significance compared to 2015, excluding the null hypothesis at 3.5σ. Beyond estimates of individual shape amplitudes, we also present model-independent reconstructions and analyses of the Planck CMB bispectrum. Our final constraint on the local primordial trispectrum shape is gNLlocal = (−5.8 ± 6.5) × 104 (68% CL, statistical), while constraints for other trispectrum shapes are also determined. Exploiting the tight limits on various bispectrum and trispectrum shapes, we constrain the parameter space of different early-Universe scenarios that generate primordial NG, including general single-field models of inflation, multi-field models (e.g. curvaton models), models of inflation with axion fields producing parity-violation bispectra in the tensor sector, and inflationary models involving vector-like fields with directionally-dependent bispectra. Our results provide a high-precision test for structure-formation scenarios, showing complete agreement with the basic picture of the ΛCDM cosmology regarding the statistics of the initial conditions, with cosmic structures arising from adiabatic, passive, Gaussian, and primordial seed perturbations.
  • Planck Collaboration; Akrami, Y.; Keihanen, E.; Kiiveri, K.; Kurki-Suonio, H.; Lindholm, V.; Savelainen, M.; Suur-Uski, A. -S.; Valiviita, J. (2020)
    We report on the implications for cosmic inflation of the 2018 release of the Planck cosmic microwave background (CMB) anisotropy measurements. The results are fully consistent with those reported using the data from the two previous Planck cosmological releases, but have smaller uncertainties thanks to improvements in the characterization of polarization at low and high multipoles. Planck temperature, polarization, and lensing data determine the spectral index of scalar perturbations to be n(s)=0.9649 +/- 0.0042 at 68% CL. We find no evidence for a scale dependence of n(s), either as a running or as a running of the running. The Universe is found to be consistent with spatial flatness with a precision of 0.4% at 95% CL by combining Planck with a compilation of baryon acoustic oscillation data. The Planck 95% CL upper limit on the tensor-to-scalar ratio, r(0.002)<0.10, is further tightened by combining with the BICEP2/Keck Array BK15 data to obtain r(0.002)<0.056. In the framework of standard single-field inflationary models with Einstein gravity, these results imply that: (a) the predictions of slow-roll models with a concave potential, V(phi) <0, are increasingly favoured by the data; and (b) based on two different methods for reconstructing the inflaton potential, we find no evidence for dynamics beyond slow roll. Three different methods for the non-parametric reconstruction of the primordial power spectrum consistently confirm a pure power law in the range of comoving scales 0.005 Mpc(-1)k less than or similar to 0.2 Mpc(-1). A complementary analysis also finds no evidence for theoretically motivated parameterized features in the Planck power spectra. For the case of oscillatory features that are logarithmic or linear in k, this result is further strengthened by a new combined analysis including the Planck bispectrum data. The new Planck polarization data provide a stringent test of the adiabaticity of the initial conditions for the cosmological fluctuations. In correlated, mixed adiabatic and isocurvature models, the non-adiabatic contribution to the observed CMB temperature variance is constrained to 1.3%, 1.7%, and 1.7% at 95% CL for cold dark matter, neutrino density, and neutrino velocity, respectively. Planck power spectra plus lensing set constraints on the amplitude of compensated cold dark matter-baryon isocurvature perturbations that are consistent with current complementary measurements. The polarization data also provide improved constraints on inflationary models that predict a small statistically anisotropic quadupolar modulation of the primordial fluctuations. However, the polarization data do not support physical models for a scale-dependent dipolar modulation. All these findings support the key predictions of the standard single-field inflationary models, which will be further tested by future cosmological observations.
  • Räsänen, Syksy; Tomberg, Eemeli (2019)
    We study the production of primordial black hole (PBH) dark matter in the case when the Standard Model Higgs coupled non-minimally to gravity is the inflaton. PBHs can be produced if the Higgs potential has a near-critical point due to quantum corrections. In this case the slow-roll approximation may be broken, so we calculate the power spectrum numerically. We consider both the metric and the Palatini formulation of general relativity. Combining observational constraints on PBHs and on the CMB spectrum we find that PBHs can constitute all of the dark matter only if they evaporate early and leave behind Planck mass relics. This requires the potential to have a shallow local minimum, not just a critical point. The initial PBH mass is then below 10(6) g, and predictions for the CMB observables are the same as in tree-level Higgs inflation, n(s) = 0.96 and r = 5 x 10(-3) (metric) or r = 4 x 10(-8) ... 2 x 10(-7) (Palatini).
  • Juselius, Mikael (Svenska handelshögskolan, 2002)
    Working Papers
    In this paper I provide some empirical answers to important questions such as the determinants of price inflation and the role of inflation polices. The results indicate that monetary policy is surprisingly impotent as a device for controlling inflation and there is little support that it influences the real variables. The low inflation after the Finnish devaluations in the beginning of 90s is foremost due to a previous imbalance in the labor markets and depressed aggregate demand.
  • Laulumaa, Laura; Markkanen, Tommi; Nurmi, Sami (2020)
    We demonstrate that adiabatic dark matter can be generated by gravity induced symmetry breaking during inflation. We study a Z(2) symmetric scalar singlet that couples to other fields only through gravity and for which the symmetry is broken by the space-time curvature during inflation when the non-minimal coupling xi is negative. We find that the symmetry breaking leads to the formation of adiabatic dark matter with the observed abundance for the singlet mass m similar to MeV and vertical bar xi vertical bar similar to 1.
  • Bracho Blok, Fernando Arturo (Helsingin yliopisto, 2020)
    We study single scalar field inflation with the standard model Higgs boson as the inflaton. We first review the homogeneous and isotropic description of the universe given by the FLRW model as well as the inflation scenario. Then we study how this scenario can can be achieved by a single scalar field minimally coupled to gravity in the slow-roll approximation. Next we study linear perturbation theory around the FLRW background. Here the perturbations are decoupled into scalar, vector and tensor perturbations which allows to study them separately. The split of physical quantities into perturbations around a background introduces gauge degrees of freedom which we address by reviewing gauge transformation of the scalar and tensor perturbations (the latter which turns out to be gauge-independent). We then use the comoving gauge and define, for the scalar perturbations, the gauge-invariant quantity known as the comoving curvature perturbation. For scalar perturbations the Einstein Field equation yields the Mukhanov-Sasaki equation, which we solve to first order in the slow-roll approximation in terms of the Mukhanov variable. We then quantize this variable using canonical quantization and calculate the power spectrum from vacuum fluctuations. We also carry the same analysis for tensor perturbations. With the power spectra at hand we introduce the spectral parameters and discuss current observations and constraints on such parameters. In Higgs inflation the Standard Model Higgs boson takes the role of the inflaton. Here the Higgs field is also coupled to the Ricci scalar, giving us a non-minimal coupling to gravity. This coupling can be transformed away using a conformal transformation at the expense of a field re-definition. This enables us to use the results reviewed thus far. At tree level we find the inflationary predictions to be in excellent agreement with current observations. However, quantum corrections complicate this picture. We review the tree level unitarity of the model and examine arguments in favour and against it. We also study how quantum corrections can qualitatively change the shape of the potential and the viability of Higgs inflation in each scenario.
  • Karciauskas, Mindaugas; Kohri, Kazunori; Mori, Taro; White, Jonathan (2018)
    In view of cosmological parameters being measured to ever higher precision, theoretical predictions must also be computed to an equally high level of precision. In this work we investigate the impact on such predictions of relaxing some of the simplifying assumptions often used in these computations. In particular, we investigate the importance of slow-roll corrections in the computation of multi-field inflation observables, such as the amplitude of the scalar spectrum P-zeta, its spectral tilt n(s), the tensor-to-scalar ratio r and the non-Gaussianity parameter f(NL). To this end we use the separate universes approach and delta N formalism, which allows us to consider slow-roll corrections to the non-Gaussianity of the primordial curvature perturbation as well as corrections to its two-point statistics. In the context of the delta N expansion, we divide slow-roll corrections into two categories: those associated with calculating the correlation functions of the field perturbations on the initial flat hypersurface and those associated with determining the derivatives of the e-folding number with respect to the field values on the initial flat hypersurface. Using the results of Nakamura & Stewart '96, corrections of the first kind can be written in a compact form. Corrections of the second kind arise from using different levels of slow-roll approximation in solving for the super-horizon evolution, which in turn corresponds to using different levels of slow-roll approximation in the background equations of motion. We consider four different levels of approximation and apply the results to a few example models. The various approximations are also compared to exact numerical solutions.
  • Enqvist, Kari; Sawala, Till; Takahashi, Tomo (2020)
    We discuss structure formation in models with a spectator field in small-field inflation which accommodate a secondary period of inflation. In such models, subgalactic scale primordial fluctuations can be much suppressed in comparison to the usual power-law Lambda CDM model while the large scale fluctuations remain consistent with current observations. We discuss how a secondary inflationary epoch may give rise to observable features in the small scale power spectrum and hence be tested by the structures in the Local Universe.
  • Lehtonen, Pyry (Helsingin yliopisto, 2017)
    The aim of this thesis is to study how the exogenous oil supply shocks generate the U.S. inflation. Exogenous oil supply shocks are determined to be political and military crises that are non-market based and affect the level of the oil supply. According to the economic theory, crises in the oil production regions cause a shortfall in the oil supply. The declined supply will raise the price of oil and therefore boost the inflation. The analyses are based on the time period of 1973 – 2016. This thesis measures the magnitude of the exogenous oil supply shocks by two methods. The first method creates a counterfactual oil production path that estimates the production that would have occurred in the absence of the shock. Comparing the actual and counterfactual production path gives an estimate for the magnitude of the shock. The second method uses the structural vector autoregression model to estimate the magnitude of the shocks. The relationship between the exogenous oil supply shocks and inflation is studied by two different methods. The autoregressive distributed lag model is constructed to see how the inflation is affected by the lags of the oil supply shocks time series and inflation. The second model is based on the structural vector autoregression model where the oil supply shocks are conducted. The impulse responses are estimated by a regression model to understand how exogenous oil supply shocks generate inflation. Both models allow the construction of the structural brake analysis. The aim of the structural brake analysis is to understand how the relationship between inflation and oil supply shocks has evolved over time. The structural brake analysis implies that the models in general give misleading results. The time period must be separated to four different subperiods in order to get adequate models. The results imply that the relationship between the oil supply shocks and inflation has changed over time. In the first period from early 1970’s to early 1980’s, the exogenous oil supply shocks had statistically significant effect on inflation. In the second and third periods from 1980’s to 2000’s, models do not find significant effect. The models give contradictory results for the fourth period in the 2010’s. The autoregressive distributed lag model does not find statistically significant effect from the exogenous oil supply shocks at inflation where impulse response analysis does. The main contributions of this thesis to the preceding literature can be divided into two sections. Firstly, the structural brake analysis has not been constructed in this field. The results give a useful insight how the relationship has evaluated over time and helps to understand the intertemporal variation of the effects. Secondly, this thesis extends the analysis to the end of 2016.
  • Paloviita, Maritta (2004)
    This paper examines empirical performance of three different Phillips curve specifications in the euro area. Instead of imposing rational expectations, direct measures, ie OECD forecasts, are used to proxy for economic agents' inflation expectations. Real marginal costs are measured in three different ways. The results suggest that with directly measured expectations the estimated New Classical Phillips curve has satisfactory statistical properties. Moreover, the driving variable enters the estimated purely forward-looking New Keynesian Phillips curve with a correct sign, but it is definitely outperformed by the New Classical and the Hybrid Phillips curve. We interpret our results as indicating that the European inflation process is not purely forward-looking, so that inflation cannot instantaneously adjust to new information. Consequently, even allowing for possible non-rationality in expectations, a lagged inflation term enters the New Keynesian Phillips curve for the European inflation dynamics. The inflation process seems to have become more forward-looking in the recent years of low and stable inflation. Furthermore, in the New Keynesian Phillips curve relationship the output gap turns out to be at least as good a proxy for real marginal costs as the labour income share.
  • Sundqvist, Johanna (2003)
    Storleken på det offentliga utvecklingsbiståndet i OECD-länderna varierar markant. FN:s rekommendation om att biståndsgivarna ska allokera 0,7 procent av sitt BNP till u-länderna, har inte uppnåtts av de flesta OECD-länder, utan majoriteten av givarna allokerar under 0,3 procent av sitt BNP till utvecklingsbistånd. Syftet med denna avhandling är att undersöka vad dessa olikheter i biståndsallokering beror på. Orsakerna bakom de varierande biståndsnivåerna under 1980- och 1990-talen, undersöks genom att jämföra biståndsgivarna utifrån fem modeller. Den första modellen undersöker om givarländernas ekonomiska välstånd inverkar på utvecklingsbiståndets nivå. Den ser på ekonomin i givarlandet i termer av BNP per capita samt ett s.k. misärindex, som mäter graden av inflation och arbetslöshet i landet. Den andra modellen undersöker om olika inhemska aktörer har haft en inverkan på utvecklingsbiståndets nivå. Modellen ser på partiernas, den allmänna opinionens samt på de kvinnliga riksdagsledamötenas inverkan i biståndspolitiken. Den tredje modellen undersöker om de sociala värderingarna i givarländerna kan förklara olikheterna i utvecklingsbiståndets nivå. De sociala värderingarna i OECD-länderna undersöks genom att se hur omfattande socialpolitik landet har, samt genom att se hur effektivt denna socialpolitik leder till inkomstjämlikhet i landet. Den fjärde modellen undersöker om biståndsgivarnas öppenhet mot andra länder och kulturer inverkar på utvecklingsbiståndets nivå. Modellen mäter ländernas öppenhet utomlands genom att se på öppenheten i flykting- och handelspolitiken. Den femte modellen undersöker om OECD-ländernas storlek i termer av folkmängd inverkar på deras biståndsnivå. Materialet för avhandlingen är tagen ifrån olika internationella organisationers statistiska verk samt från tidigare studier som gjorts om ämnet. Som metod har använts både kvalitativ och kvantitativ analys med hjälp av spridningsdiagram, korrelation och regression. Resultaten av studien visar att länder med en hög biståndsnivå har starkare och mer solidariska sociala värderingar. Detta kan ses från den stora andel sociala utgifter av BNP som högbiståndsgivarna har, den jämnare inkomstfördelningen, den större andelen beviljade uppehållstillstånd för flyktingar samt den större andelen kvinnliga riksdagsledamöter. Flyktingpolitiken och kvinnornas inflytande kan därav ses som mått på landets sociala värderingar. Den allmänna opinionen och folkmängden i givarlandet har en svag inverkan på utvecklingsbiståndet, medan givarlandets ekonomi, partifördelning och handelspolitik inte uppvisar några starka samband med utvecklingsbistånd.
  • Bernal, Nicolas; Rubio, Javier; Veermäe, Hardi (2020)
    In the Starobinsky model of inflation, the observed dark matter abundance can be produced from the direct decay of the inflaton field only in a very narrow spectrum of closeto-conformal scalar fields and spinors of mass similar to 10(7) GeV. This spectrum can be, however, significantly broadened in the presence of effective non-renormalizable interactions between the dark and the visible sectors. In particular, we show that UV freeze-in can efficiently generate the right dark matter abundance for a large range of masses spanning from the keV to the PeV scale and arbitrary spin, without significantly altering the heating dynamics. We also consider the contribution of effective interactions to the inflaton decay into dark matter.