Bounds For The Tail Distribution Of The Sum Of Digits Of Prime Numbers

Let s_q(n) denote the base q sum of digits function, which for n<x, is centered around (q-1)/2 log_q x. In Drmota, Mauduit and Rivat's 2009 paper, they look at sum of digits of prime numbers, and provide asymptotics for the size of the set {p<x, p prime : s_q(p)=alpha(q-1)log_q x} where alpha lies in a tight range around 1/2. In this paper, we examine the tails of this distribution, and provide the lower bound |{p < x, p prime : s_q(p)>alpha(q-1)log_q x}| >>x^{2(1-alpha)}e^{-c(log x)^{1/2+epsilon}} for 1/2<alpha<0.7375. To attain this lower bound, we note that the multinomial distribution is sharply peaked, and apply results regarding primes in short intervals. This proves that there are infinitely many primes with more than twice as many ones than zeros in their binary expansion.Comment: 4 page

On Improving Roth's Theorem in the Primes

Let $A\subset\left\{ 1,\dots,N\right\}$ be a set of prime numbers containing no non-trivial arithmetic progressions. Suppose that $A$ has relative density $\alpha=|A|/\pi(N)$, where $\pi(N)$ denotes the number of primes in the set $\left\{ 1,\dots,N\right\}$. By modifying Helfgott and De Roton's work, we improve their bound and show that $$\alpha\ll\frac{\left(\log\log\log N\right)^{6}}{\log\log N}.$$Comment: 14 pages, to appear in Mathematik

A Density Increment Approach to Roth's Theorem in the Primes

We prove that if $A$ is any set of prime numbers satisfying $$\sum_{a\in A}\frac{1}{a}=\infty,$$ then $A$ must contain a $3$-term arithmetic progression. This is accomplished by combining the transference principle with a density increment argument, exploiting the structure of the primes to obtain a large density increase at each step of the iteration. The argument shows that for any $B>0$, and $N>N_{0}(B)$, if $A$ is a subset of primes contained in $\{1,\dots,N\}$ with relative density $\alpha(N)=(|A|\log N)/N$ at least $$\alpha(N)\gg_{B}\left(\log\log N\right)^{-B}$$ then $A$ contains a $3$-term arithmetic progression.Comment: This has paper has been withdrawn due to an error in equation (2.8). This error comes from the linearization step. I believe that the density increment argument can be corrected, and a similar bound can be obtained by moving entirely to Bohr sets. Currently this paper has a hole so I am removing it from the arXi

The Median Largest Prime Factor

Let $M(x)$ denote the median largest prime factor of the integers in the interval $[1,x]$. We prove that $$M(x)=x^{\frac{1}{\sqrt{e}}\exp(-\text{li}_{f}(x)/x)}+O_{\epsilon}(x^{\frac{1}{\sqrt{e}}}e^{-c(\log x)^{3/5-\epsilon}})$$ where $\text{li}_{f}(x)=\int_{2}^{x}\frac{\{x/t\}}{\log t}dt$. From this, we obtain the asymptotic $$M(x)=e^{\frac{\gamma-1}{\sqrt{e}}}x^{\frac{1}{\sqrt{e}}}(1+O(\frac{1}{\log x})),$$ where $\gamma$ is the Euler Mascheroni constant. This answers a question posed by Martin, and improves a result of Selfridge and Wunderlich.Comment: 7 page

Monochromatic Equilateral Triangles in the Unit Distance Graph

Let $\chi_{\Delta}(\mathbb{R}^{n})$ denote the minimum number of colors needed to color $\mathbb{R}^{n}$ so that there will not be a monochromatic equilateral triangle with side length $1$. Using the slice rank method, we reprove a result of Frankl and Rodl, and show that $\chi_{\Delta}\left(\mathbb{R}^{n}\right)$ grows exponentially with $n$. This technique substantially improves upon the best known quantitative lower bounds for $\chi_{\Delta}\left(\mathbb{R}^{n}\right)$, and we obtain $$\chi_{\Delta}\left(\mathbb{R}^{n}\right)>(1.01446+o(1))^{n}.$$Comment: 4 page

Primitive points in rational polygons

Let $\mathcal A$ be a star-shaped polygon in the plane, with rational vertices, containing the origin. The number of primitive lattice points in the dilate $t\mathcal A$ is asymptotically $\frac6{\pi^2}$ Area$(t\mathcal A)$ as $t\to \infty$. We show that the error term is both $\Omega_\pm\big( t\sqrt{\log\log t} \big)$ and $O(t(\log t)^{2/3}(\log\log t)^{4/3})$. Both bounds extend (to the above class of polygons) known results for the isosceles right triangle, which appear in the literature as bounds for the error term in the summatory function for Euler's $\phi(n)$.Comment: 17 page

Currency Option Pricing in Credible Target Zones

This paper develops a model for valuing options on a currency which is maintained within a band. The starting point of our model is the well known Krugman model for exchange-rate behavior within a target zone. Results from model runs provide insight into evidence reported by other authors of mispricing of currency options by extensions of the Black-Scholes model.

Upper bounds for sunflower-free sets

A collection of $k$ sets is said to form a $k$-sunflower, or $\Delta$-system, if the intersection of any two sets from the collection is the same, and we call a family of sets $\mathcal{F}$ sunflower-free if it contains no sunflowers. Following the recent breakthrough of Ellenberg and Gijswijt and Croot, Lev and Pach we apply the polynomial method directly to Erd\H{o}s-Szemer\'{e}di sunflower problem and prove that any sunflower-free family $\mathcal{F}$ of subsets of $\{1,2,\dots,n\}$ has size at most $$|\mathcal{F}|\leq3n\sum_{k\leq n/3}\binom{n}{k}\leq\left(\frac{3}{2^{2/3}}\right)^{n(1+o(1))}.$$ We say that a set $A\subset(\mathbb Z/D \mathbb Z)^{n}=\{1,2,\dots,D\}^{n}$ for $D>2$ is sunflower-free if every distinct triple $x,y,z\in A$ there exists a coordinate $i$ where exactly two of $x_{i},y_{i},z_{i}$ are equal. Using a version of the polynomial method with characters $\chi:\mathbb{Z}/D\mathbb{Z}\rightarrow\mathbb{C}$ instead of polynomials, we show that any sunflower-free set $A\subset(\mathbb Z/D \mathbb Z)^{n}$ has size $$|A|\leq c_{D}^{n}$$ where $c_{D}=\frac{3}{2^{2/3}}(D-1)^{2/3}$. This can be seen as making further progress on a possible approach to proving the Erd\H{o}s-Rado sunflower conjecture, which by the work of Alon, Sphilka and Umans is equivalent to proving that $c_{D}\leq C$ for some constant $C$ independent of $D$.Comment: 5 page

Who will become dominant? Investigating the roles of individual behaviour, body size, and environmental predictability in brown trout fry hierarchies

This paper presents a study investigating performance of brown trout fry, with different behavioural characteristics, in environments differing in food predictability. Based on previous experimental findings, we hypothesised&nbsp;that more active individuals would be favoured by a predictable environment, as compared to an unpredictable&nbsp;environment, as a consequence of being more aggressive and likely to dominate the best feeding stations. This&nbsp;hypothesis was not supported, as more active individuals instead tended to perform better, in terms of growth&nbsp;and survival, in unpredictable environments. However, this effect may stem from initial size differences, as more active fish also tended to be larger. In predictable environments, no trends between activity (or size) and performance&nbsp;were detected. Dominant individuals could be identified based on lighter body colouration in 9 out of&nbsp;10 rearing tanks, but dominance appeared not to be related to activity score. The results highlight a potential advantage of more active and/or larger fry in unpredictable environments, while performance in predictable environments is likely depending on other phenotypic characteristics. Our general experimental approach can&nbsp;be useful for further developments in the investigation of performance of different ethotypes of brown trout fry