We study adiabatic (curvature) and entropy (isocurvature) perturbations produced during a period of cosmological inflation that is driven by multiple scalar fields with an arbitrary interaction potential. A local rotation in field space is performed to separate out the adiabatic and entropy modes. The resulting field equations show explicitly how on large scales entropy perturbations can source adiabatic perturbations if the background solution follows a curved trajectory in field space, and how adiabatic perturbations cannot source entropy perturbations in the long-wavelength limit. It is the effective mass of the entropy field that determines the amplitude of entropy perturbations during inflation. We present two applications of the equations. First, we show why one in general expects the adiabatic and entropy perturbations to be correlated at the end of inflation, and calculate the cross-correlation in the context of a double inflation model with two non-interacting fields. Second, we consider two-field preheating after inflation, examining conditions under which entropy perturbations can alter the large-scale curvature perturbation and showing how our new formalism has advantages in numerical stability when the background solution follows a non-trivial trajectory in field space.

Employing Fermi-LAT gamma ray observations, several independent groups have found excess extended gamma ray emission at the Galactic center (GC). Both, annihilating dark matter (DM) or a population of ∼ 10 3 unresolved millisecond pulsars (MSPs) are regarded as well motivated possible explanations. However, there is significant uncertainties in the diffuse galactic background at the GC. We have performed a revaluation of these two models for the extended gamma ray source at the GC by accounting for the systematic uncertainties of the Galactic diffuse emission model. We also marginalize over point source and diffuse background parameters in the region of interest. We show that the excess emission is significantly more extended than a point source. We find that the DM (or pulsars population) signal is larger than the systematic errors and therefore proceed to determine the sectors of parameter space that provide an acceptable fit to the data. We found that a population of order a 1000 MSPs with parameters consistent with the average spectral shape of Fermi-LAT measured MSPs was able to fit the GC excess emission. For DM, we found that a pure τ + τ − annihilation channel is not a good fit to the data. But a mixture of τ + τ − and bb with a σv of order the thermal relic value and a DM mass of around 20 to 60 GeV provides an adequate fit.

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An anomalous gamma-ray excess emission has been found in Fermi Large Area Telescope data 1 covering the centre of the Galaxy 2, 3 . Several theories have been proposed for this 'Galactic Centre Excess'. They include self-annihilation of dark matter particles 4 , an unresolved population of millisecond pulsars 5 , an unresolved population of young pulsars 6 , or a series of burst events 7 . Here we report on a new analysis that exploits hydrodynamical modelling to register the position of interstellar gas associated with diffuse Galactic gamma-ray emission. We find evidence that the Galactic Centre Excess gamma rays are statistically better described by the stellar over-density in the Galactic bulge and the nuclear stellar bulge, rather than a spherical excess. Given its non-spherical nature, we argue that the Galactic Centre Excess is not a dark matter phenomenon but rather associated with the stellar population of the Galactic bulge and nuclear bulge.The main challenge in pinning down the properties of the Galactic Centre Excess (GCE) is the modelling of diffuse Galactic emission from the interaction of cosmic rays with interstellar gas and radiation fields, by far the dominant source of gamma-rays in this region. The Fermi-Large Area Telescope (LAT) Collaboration designed a diffuse Galactic emission model based on a template 8 approach that is optimized to single-out gamma-ray point sources. This approach presupposes that the diffuse Galactic emission can be modelled as a linear combination of interstellar gas, inverse Compton maps, and several other diffuse components. Due to the limited kinematic resolution of gas tracers towards the Galactic Centre (GC), interstellar gas correlated gamma rays from the GC direction are difficult to disentangle. Previous studies 3, 4, 9 utilized interstellar gas maps that were constructed with an interpolation approach that assumed circular motion of interstellar gas. This kinematic assumption provides for an estimate of the distance to a part of the interstellar gas. However, it is well established that the Galaxy contains a central bar which causes non-circular motion of interstellar gas in its inner regions, so assuming circularity introduces a significant and avoidable bias to gamma-ray analyses of the GC region 10 .We use Fermi-LAT data accumulated between August 4, 2008 and September 4, 2015 in the 15 • ×15 • region around the GC. Hydrodynamical simulations 10 that account for the effects of the Galactic bar were used to better determine the diffuse Galactic gamma-ray emission. To evaluate the impact that the choice of interstellar gas models have on our results, we also constructed atomic and molecular hydrogen gas maps using an interpolation approach that reproduced those used in most previous gamma-ray analyses of the GC. We split each into 4 concentric rings, each with its own normalization parameter. Details of the model components and approach are provided in the Methods section.Interstellar gas map templates constructed using the results of hydrodynamical simulati...

We introduce a class of models in which statistical isotropy is broken spontaneously in the CMB by a non-linear response to long-wavelength fluctuations in a mediating field. These fluctuations appear as a gradient locally and pick out a single preferred direction. The non-linear response imprints this direction in a range of multipole moments. We consider two manifestations of isotropy breaking: additive contributions and multiplicative modulation of the intrinsic anisotropy. Since WMAP exhibits an alignment of power deficits, an additive contribution is less likely to produce the observed alignments than the usual isotropic fluctuations, a fact which we illustrate with an explicit cosmological model of long-wavelength quintessence fluctuations. This problem applies to other models involving foregrounds or background anisotropy that seek to restore power to the CMB. Additive models that account directly for the observed power exacerbate the low power of the intrinsic fluctuations. Multiplicative models can overcome these difficulties. We construct a proof of principle model that significantly improves the likelihood and generates stronger alignments than WMAP in 30-45% of realizations.

There is growing evidence that the Galactic Center Excess identified in the Fermi-LAT gamma-ray data arises from a population of faint astrophysical sources. We provide compelling supporting evidence by showing that the morphology of the excess traces the stellar over-density of the Galactic bulge. By adopting a template of the bulge stars obtained from a triaxial 3D fit to the diffuse near-infrared emission, we show that it is detected at high significance. The significance deteriorates when either the position or the orientation of the template is artificially shifted, supporting the correlation of the gamma-ray data with the Galactic bulge. In deriving these results, we have used more sophisticated templates at low-latitudes for the Fermi bubbles compared to previous work and the three-dimensional Inverse Compton (IC) maps recently released by the GALPROP team. Our results provide strong constraints on Millisecond Pulsar (MSP) formation scenarios proposed to explain the excess. We find that an admixture formation scenario, in which some of the relevant binaries are primordial and the rest are formed dynamically, is preferred over a primordial-only formation scenario at 7.6σ confidence level. Our detailed morphological analysis also disfavors models of the disrupted globular clusters scenario that predict a spherically symmetric distribution of MSPs in the Galactic bulge. For the first time, we report evidence of a high energy tail in the nuclear bulge spectrum that could be the result of IC emission from electrons and positrons injected by a population of MSPs and star formation activity from the same site. pulsars, in the form of either old "recycled" millisecond pulsars [13,18], or young pulsar remnants from Galactic Center supernovae [19,20]. The gamma-ray spectra of known pulsars are similar to the GCE, and the capture of pulsars onto the Galactic Center region by Globular Cluster disruptions could explain the GCE's quasi-spherical spatial distribution [21,22]. Other explanations for the GCE discussed in the literature include outbursts of cosmic-ray production by the central supermassive black hole (e.g., [23]).While pulsars are a natural astrophysical candidate, there is ongoing debate regarding the consistency of the luminosity function required to explain the GCE with that measured for the pulsar population observed elsewhere as point sources [24][25][26][27]. Nevertheless, there are strengthening indications that the GCE may have an astrophysical origin. Cosmic-ray interactions in the Galactic Center region are notoriously complex to model. New analyses have cast doubt on some of the main properties claimed previously for the GCE. First, the energy spectrum of the GCE is subject to large systematic uncertainties arising from the incomplete understanding of cosmic-ray interactions in the Galactic Center region (e.g., [13][14][15]17]). A variety of scenarios might, therefore, describe the GCE based on the energy spectrum alone. Second, it has been argued that the photon count distribution of the GCE is ...

We compare the latest cosmic microwave background data with theoretical predictions including correlated adiabatic and CDM isocurvature perturbations with a simple power-law dependence. We find that there is a degeneracy between the amplitude of correlated isocurvature perturbations and the spectral tilt. A negative (red) tilt is found to be compatible with a larger isocurvature contribution. Estimates of the baryon and CDM densities are found to be almost independent of the isocurvature amplitude. The main result is that current microwave background data do not exclude a dominant contribution from CDM isocurvature fluctuations on large scales. Maxima [3] data have shown evidence for three peaks in the cosmic microwave background (CMB) temperature anisotropy power spectrum as expected in inflationary scenarios. In this context the CMB data support the current 'concordance' model based on a spatially flat Friedmann-Robertson-Walker universe dominated by cold dark matter and a cosmological constant [4]. In addition, the CMB data no longer shows any signs of being in conflict with the big bang nucleosynthesis data [5].In the studies which have estimated the cosmological and primordial parameters with these new data sets, only the case of purely adiabatic perturbations has been considered so far. That is, the perturbation in the relative number densities of different particle species is taken to be zero. Although this assumption is justified for perturbations originating from single field inflationary models, it does not necessarily follow when there is more than one field present during inflation [6][7][8][9][10]. Other possible primordial modes are isocurvature [11,12] (also referred to as "entropy") modes in which the particle ratios are perturbed but the total energy density is unperturbed in the comoving gauge.Most previous studies have examined the extent to which a statistically independent isocurvature contribution to the primordial perturbations may be constrained by CMB and large-scale structure data [13,14]. It has recently been shown that multi-field inflationary models in general produce correlated adiabatic and isocurvature perturbations [7][8][9][10]. These correlations can dramatically change the observational effect of adding isocurvature perturbations [15,12]. Up until now, only the case of scale-invariant correlated adiabatic and entropy perturbations has been considered. Trotta et al. [16] found (with an earlier CMB dataset) that in this case the cold dark matter (CDM) isocurvature mode was likely to be very small if not entirely absent, though they did find that a neutrino isocurvature mode contribution [12] was not ruled out. In this letter we examine to what extent a correlated CDM isocurvature mode is consistent with the recent CMB data when a tilted power law spectrum is allowed.Non-adiabatic perturbations are produced during a period of slow-roll inflation in the presence of two or more light scalar fields, whose effective masses are less than the Hubble rate. On sub-horizon scales, fluc...

The Fermi-LAT data appear to have an excess of gamma rays from the inner 150 pc of the Galactic Center. The main explanations proposed for this are: an unresolved population of millisecond pulsars (MSPs), dark matter (DM) annihilation, and nonthermal bremsstrahlung produced by a population of electrons interacting with neutral gas in molecular clouds. The first two options have spatial templates well fitted by the square of a generalized Navarro-Frenk-White (NFW) profile with inner slope γ = 1.2. We model the third option with a 20-cm continuum emission Galactic Ridge template. A template based on the HESS residuals is shown to give similar results. The gamma-ray excess is found to be best fit by a combination of the generalized NFW squared template and a Galactic Ridge template. We also find the spectra of each template is not significantly affected in the combined fit and is consistent with previous single template fits. That is the generalized NFW squared spectrum can be fit by either of order 1000 unresolved MSPs or DM with mass around 30 GeV, a thermal cross section, and mainly annihilating to bb quarks. While the Galactic Ridge continues to have a spectrum consistent with a population of nonthermal electrons whose spectrum also provides a good fit to synchrotron emission measurements. We also show that the current DM fit may be hard to test, even with 10 years of Fermi-LAT data, especially if there is a mixture of DM and MSPs contributing to the signal, in which case the implied DM cross section will be suppressed.