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I will discuss the growth of quantum fluctuations of an axion field rolling down a potential with multiple minima. This effect is particularly relevant for the relaxion mechanism, in which provides an alternarive stopping mechanism, thus modifying the relevant parameter space. I will present new lattice results, and discuss some cosmological aspects.
To solve the hierarchy problem, the relaxion must remain trapped in the correct minimum, even if the electroweak symmetry is restored after reheating. In this scenario, the relaxion starts rolling again until the backreaction potential, with its set of local minima, reappears. Depending on the time of barrier reappearance, Hubble friction alone may be insufficient to retrap the relaxion in a...
We study the thermal production of axions over different scales especially around the QCD and electroweak phase transitions in the early universe. We focus on the most motivated axion models (KSVZ and DFSZ) and investigate how the thermal history can influence on the production rate of hot axion as dark radiation. This can lead to predictions for the future measurements of the cosmic microwave...
The calculation of the solar axion flux has recently generated much attention, and it has been realised that axions can be powerful tools for studying solar metal abundances and magnetic fields.
The feasibility of such studies depends on our ability to accurately predict the solar axion flux. In this talk, I will present an overview of solar models and opacity codes and summarise the...
This talk would be based on the paper by Sebastian Hoof, David J. E. Marsh and myself, that was uploaded on arXiv recently (https://arxiv.org/abs/2108.09563).
We review results from QCD axion string and domain wall simulations and propagate the associ-
ated uncertainties into the calculation of the axion relic density. This allows us to compare different
results in the literature and,...
A fast-spinning axion can dominate the Universe at early times and generates the so-called kination era. The presence of kination imprints a smoking-gun spectral enhancement in the primordial gravitational wave (GW) background. Current and future-planned GW observatories could constrain particle theories that generate the kination phase. Surprisingly, the viable parameter space allows for a...
Axion-like particles (ALPs) are leading dark matter candidates originally motivated by the strong CP problem and also arise in theories of string compactifications. We present a sensitive probe for ALPs as ultra-light dark matter - the birefringence in the cosmic microwave background (CMB). Birefringence arises from the oscillating ALP field's inhomogeneity and is also relevant for laboratory...
In this work, we have studied the production of baryon asymmetry and gravitino dark matter in contemporary times from the decay of the same source. In accomplishing a physical model to study these phenomenologies we have considered R-parity violating SUSY and the decay of Bino like neutralino which generates the baryon asymmetry and DM. In continuation of the previous work, we have added here...
Fragmentation of the axion field may produce the observed DM abundance, which makes it possible for ALP DM to appear with lower values of the axion decay constant than those allowed by the conventional misalignment mechanism. Previously, kinetic misalignment has been proposed to open up this parameter space. We find that for a large range of parameters the field becomes fragmented before...
We investigate the potential of type II supernovae (SNe) to constrain axion-like particles (ALPs) coupled simultaneously to nucleons and electrons. ALPs coupled to nucleons can be efficiently produced in the SN core via nucleon-nucleon bremsstrahlung and, for a wide range of parameters, leave the SN unhindered, producing a large ALP flux.
For masses exceeding 1 MeV, these ALPs would decay...
Recently, the Planck 2018 polarization data of cosmic microwave background (CMB) radiation suggested the non-zero rotation angle of CMB polarization plane $\beta=0.35\pm0.14 {\rm deg}$, which is called cosmic birefringence. Cosmic birefringence is predicted if an axion-like particle (ALP) moves after the recombination. We show that this naturally happens if the ALP is coupled to the dark...
In this talk, we reanalyze the multi-component strongly interacting massive particle (mSIMP) scenario using an effective operator approach. As in the single-component SIMP case, the total relic abundance of mSIMP dark matter (DM) is determined by the coupling strengths of $3 \to 2$ processes achieved by a five-point effective operator. Intriguingly, we find that there is an unavoidable $2 \to...
The direct detection of sub-GeV dark matter interacting with nucleons is hampered by the low recoil energies induced by scatterings in the detectors. This experimental difficulty is avoided in the scenario of boosted dark matter where a component of dark matter particles is endowed with large kinetic energies. In this Letter, we point out that the current evaporation of primordial black holes...
We propose a novel mechanism for the production of dark matter (DM) from a thermal bath, based on the idea that DM particles $\chi$ can transform heat bath particles $\psi$: $\chi \psi \rightarrow \chi \chi$. For a small initial abundance of $\chi$ this leads to an exponential growth of the DM number density, in close analogy to other familiar exponential growth processes in nature. We...
In this talk, we will provide a comprehensive analysis of the prospect to realize Dark Matter (DM) and to enhance the Electroweak PhaseTransition (EWPhT) with an Inert Doublet. Taking the latest constraints from collider physics and direct-detection experiments into account, we will investigate the possibility of a strong first-order EWPhT via one or two steps in combination with a significant...
We consider multiverse models in two-dimensional linear dilaton-gravity theories as toy models of false vacuum eternal inflation. Coupling conformal matter we calculate the Von Neumann entropy of subregions. When these are sufficiently large we find that an island develops covering most of the rest of the multiverse, leading to a Page-like transition. This resonates with a description of...
We consider the possibility that the majority of dark matter in our Universe consists of black holes of primordial origin. We examine the effects of stochastic inflation and an early matter-dominated era on the abundance of these black holes. We show that the power spectrum of comoving curvature perturbations computed in stochastic inflation matches the result obtained by solving the...
In this talk, we will present a renormalizable polynomial inflation model, focusing on the small field scenario. We show that the CMB data can be fitted perfectly with a perturbated inflection-point. In particular, the running of the spectral index is predicted to be $\alpha \simeq -1.43 \times 10^{-3}$, which could be tested by next generation CMB experiment. We also analyze reheating...
The observation of stochastic gravitational wave backgrounds from first-order phase transitions in the early Universe is promising to become a feasible test for high energy physics. In this talk, I will show how observable signals can be obtained from strong first-order phase transitions in a dark sector. If the dark sector is initially without thermal contact to the particle species of the...
A mechanism for the formation of primordial black holes is proposed. Here, heavy quarks of a confining gauge theory produced by de Sitter fluctuations are pushed apart by inflation and get confined after horizon re-entry. The large amount of energy stored in the QCD string connecting the quark pair leads to black-hole formation. These are much lighter and can be of higher spin than those...
We discuss the interplay of wave package decoherence and decoherence induced by quantum gravity via interactions with spacetime foam for high energy astrophysical neutrinos. In this context we point out a compelling consequence of the expectation that quantum gravity should break global symmetries, namely that quantum-gravity induced decoherence can provide both a powerful tool for the search...
The bubble wall velocity in first-order cosmological phase transitions is crucial for phenomenological studies of, for example, the production of stochastic gravitational waves and electroweak baryogenesis. It is commonly expected that a friction force on the bubble wall can only arise from out-of-equilibrium effects. Here we study the bubble wall motion in local thermal equilibrium. We...
Primordial black holes hypothetically generated in the first instants of life of the Universe are potential dark matter candidates. Focusing on primordial black holes masses in the range $[5 \times 10^{14} − 5\times 10^{15}]$g, we point out that the neutrinos emitted by primordial black holes evaporation can interact through the coherent elastic neutrino-nucleus scattering producing an...
Breaking of a $U(1)_{B-L}$ local symmetry, a feature that occurs in a wide variety of the Standard Model ultraviolet completions, can lead to generation of cosmic strings which can lead to an observable signal in gravitational waves (GWs). In this talk we will discuss how the GWs can be used to probe leptogenesis mechanism due to heavy neutrino decay. In particular, we will look into the...
The fractional dark energy (FDE) model describes the accelerated expansion of the Universe through a non-relativistic gas of particles with a non-canonical kinetic term. This term is proportional to the absolute value of the three-momentum to the power of 3w, where w is simply the dark energy equation of state parameter, and the corresponding energy leads to an energy density that mimics the...
I discuss to what extend LISA can observe features of gravitational wave spectra originating from cosmological first-order phase transitions. I focus on spectra which are of the form of double-broken power laws. These spectra are predicted by hydrodynamic simulations and also analytical models such as the sound shell model. I argue that the ratio of the two break frequencies is an interesting...
Appearance of cosmic strings in the early Universe is a common manifestation of new physics typically linked to some high energy scale. In this talk, I will discuss a different situation, where a model underlying cosmic string formation is approximately scale free. String tension is naturally related to the square of the temperature of the hot primordial plasma in such a setting, and hence...
Intensity Mapping (IM) of line emission targets the Universe from present
time up to redshifts beyond ten when the Universe reionized and the first
galaxies formed, from small to largest scales. Similar to CMB measurements,
the power spectra of intensity fluctuations inform about the underlying cosmology;
imagine the information encoded in thousands of intensity maps at
different...
The $\sigma_8$-tension of Planck data with weak lensing and redshift surveys is one of the main problems with the $\Lambda$CDM model of cosmology. We show that the tension can be alleviated by introducing an interaction between dark matter and neutrinos. We model the interaction using a linear Boltzmann treatment, introducing a novel implementation that for the first time uses the full massive...
The recent very-high-energy (VHE) gamma-ray observations of gamma-ray bursts (GRBs) in their afterglow phase motivate a review of the established fireball model in which a relativistic blast wave accelerates electrons in the forward shock, which then radiate via the synchrotron process and inverse Compton scattering on these synchrotron photons (synchrotron self-Compton). We use the rich...
Analytical models of structure formation are an important tool, complementary to N-body simulations, to investigate the formation of Dark Matter structures and the dependence of their statistics on cosmological parameters. They rely on some non-linear map, typically inferred from spherical collapse, to relate topological features of the initial density field (number of maxima, minima, saddles,...
We propose a new mechanism for baryogenesis, in which baryon asymmetry is generated by absorption of a new particle $X$ carrying baryon number onto Primordial Black Holes (PBHs). Due to CP violation of $X$ and $\overline{X}$ scattering with the plasma surrounding PBHs, the two conjugate particles are differently absorbed by PBHs, leading to the production of an asymmetry in the $X$ sector. The...
In the recent years, Leptogenesis and Electroweak Baryogenesis have been a developing ground for non-equilibrium thermal quantum field theory techniques. In particular, the generation of a CP asymmetry can be described in terms of the Schwinger-Dyson (SD) equations evaluated over a closed time path (CTP) in the Schwinger-Keldysh formalism. Based on this SD approach the equations of motion for...
Neutron-antineutron ($n$-$\bar{n}$) oscillation is a baryon number violating process that will be probed at an unprecedented sensitivity in near future experiments at ESS and DUNE. We study potential impacts of the $n$-$\bar{n}$ oscillation mechanism on the baryon asymmetry of the Universe. Using an effective field theory framework, as well as a simplified model for one of two possible...
I will discuss a recently proposed class of models where Dark Matter (DM) is produced via an inverse phase transition. The inverse phase transition can be caused by coupling to some cosmological field. For instance, this field can be the Ricci scalar, as in e-Print: 2004.03410; primordial magnetic field, as in e-Print: 2010.03383; or thermal fluctuations of other fields, as in e-Print:...
