Activities This Week

The Mobius function is one of the most important arithmetic functions. There is a vague yet well known principle regarding its randomness properties called the “Mobius randomness law”. It basically states that the Mobius function should be orthogonal to any “structured” sequence. P. Sarnak suggested a far reaching conjecture as a possible formalization of this principle. He conjectured that “structured sequences” should correspond to sequences arising from deterministic dynamical systems. I will describe progress in recent years towards these conjectures building on major advances in ergodic theory, additive combinatorics, and analytic number theory.

משפט דה-רם מאחד ומכליל הרבה מהמשפטים שלומדים בשבועות האחרונים של קורס בחשבון דיפרנציאלי גאומטרי. הוא מהווה דוגמה ראשונה לאינטראקציה חזקה בין טופולוגיה ומשוואות דיפרנציאליות. ניתן גם לראות משפט זה כנקודת התחלה לאספקטים מרכזיים של הגאומטריה והאריתמטיקה של ימינו. אני אסביר מה המשפט אומר, ואספר קצת על התפתחויות מודרניות.

אחרי ההרצאה, בשעה 19:30, נקיים “ג’אם” מוסיקה חופשי, מוזמנים לבוא עם כלי נגינה ולנגן, או סתם לבוא לשמוע

Lara—Srinivas—Stix, building on joint work with Esnalut, have recently shown that the etale fundamental group of a connected proper scheme over an algebraically closed field is topologically finitely presented, thus answering a question raised in SGA. The proof relies on a finite presentation criterion of Lubotzky for profinite groups, resolutions of singularities/alterations, a theorem of Deligne—Ilusie on the Euler characteristic, as well as other modern and classical results in (arithmetic) algebraic geometry.

Temporo-spatial differentiations are ergodic averages on a probabilistic dynamical system $(X, \mu, T)$ taking the form $\left( \frac{1}{\mu(C_k)} \int_{C_k} \frac{1}{k} \sum_{j = 0}^{k - 1} T^j f \mathrm{d} \mu \right)_{k = 1}^\infty $ where $C_k \subseteq X$ are measurable sets of positive measure, and $f \in L^\infty(X, \mu)$. These averages combine both the dynamics of the transformation and the structure of the underlying probability space $(X, \mu)$. We will discuss the motivations behind studying these averages, results concerning the limiting behavior of these averages and, time permitting, discuss generalizations to non-autonomous dynamical systems. Joint work with Idris Assani.